home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Multi-CD Magazin 1994 April
/
MultiCDMagazin0494.iso01.iso
/
sw_top10
/
skymp13
/
skymap.txt
< prev
next >
Wrap
Text File
|
1993-05-30
|
118KB
|
3,066 lines
SkyMap v1.3 User Guide SkyMap v1.3 User Guide SkyMap v1.3 User Guide
C A Marriott C A Marriott C A Marriott
May 1993 May 1993 May 1993
_______
____|__ | (R)
--| | |-------------------
| ____|__ | Association of
| | |_| Shareware
|__| o | Professionals
-----| | |---------------------
|___|___| MEMBER
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Respectfully dedicated to the memory of:
Francis R Scobee
Michael J Smith
Ellison S Onizuka
Judith A Resnick
Ronald E McNair
Gregory Jarvis
S Christa McAuliffe
the crew of Challenger flight STS 51-L, 28th January 1986
and to all who have lived - and died - for The Dream.
"Oh, I have slipped the surly bonds of earth,
And danced the skies on laughter-silvered wings;
Sunward I've climbed and joined the tumbling mirth
Of sun-split clouds -- and done a hundred things
You have not dreamed of -- wheeled and soared and swung
High in the sunlit silence. Hov'ring there,
I've chased the shouting wind along and flung
My eager craft through footless halls of air.
Up, up the long, delirious, burning blue
I've topped the wind-swept heights with easy grace,
Where never lark, or even eagle, flew;
And, while with silent, lifting mind I've trod
The high, untrespassed sanctity of space,
Put out my hand, and touched the face of God."
"High Flight" John G Magee Jr, 1943
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Table of Contents
Introduction................................................1
What is Shareware? .....................................2
Disclaimer Agreement ...................................2
ASP Ombudsman Statement ................................3
Contacting the Author ..................................3
Registering SkyMap .....................................4
System Requirements ....................................6
Setting Up SkyMap...........................................7
Installing the Software ................................7
Configuring SkyMap for your Location ...................8
Horizon Maps................................................11
Drawing a Horizon Map ..................................11
Horizon Map Options ....................................11
Viewpoint .........................................11
Time ..............................................12
Observer ..........................................12
Stars .............................................13
Star Labels .......................................14
Labels ............................................14
Constellation Names ...............................16
RNGC Objects ......................................16
Colours ...........................................17
Reduce Positions ..................................17
Draw ..............................................18
Using the Horizon Map ..................................18
Setting the Visibility of Objects .................18
Changing the map scale ............................18
Identifying Objects on the Map ....................19
Zooming to an Area Map ............................23
Printing the Map ..................................24
Sky Area Maps...............................................26
Drawing a Sky Area Map .................................26
Sky Area Map Options ...................................26
Viewpoint .........................................26
Time ..............................................27
Observer ..........................................27
Stars .............................................28
Stars Labels ......................................29
Constellation Names ...............................30
RNGC Objects ......................................30
Colours ...........................................31
Draw ..............................................31
Using the Sky Area Map .................................32
Setting the Visibility of Objects .................32
Changing the map scale ............................32
Identifying Objects on the Map ....................32
Zooming to an Area Map ............................32
Printing the Map ..................................33
Displaying Pictures.........................................34
Picture Formats ........................................34
Displaying Pictures Manually ...........................34
Displaying Pictures Automatically ......................34
i
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Obtaining Picture Files ................................35
Appendix A: Data Sources and Precision.....................37
Stars ..................................................37
Planets and Sun ........................................37
Moon ...................................................37
Non-Stellar Objects ....................................38
Time Corrections .......................................38
Appendix B: Dreyer Object Descriptions.....................40
Appendix C: SkyMap Release History.........................44
ii
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Introduction Introduction Introduction
SkyMap is a "Planetarium" program for Microsoft Windows version
3.1 or later. It will display a map of the sky as seen from any
point on Earth for any date between 4000BC and 8000AD. Two
different types of map can be drawn - a "Horizon" map showing the
observer's local horizon, and a "Sky Area" map showing a detailed
view of a small area of the sky. You can get information about
any object displayed on the map by simply pointing at the object
with the mouse and clicking the button. The display of
additional information, such as constellation figures or star
labels can be switched on and off with a click of the mouse
button, making it easy to see exactly what you want without being
overwhelmed by unwanted information. When you have the map
exactly as you want it, you can print it on any printer supported
by Windows, in either black and white or colour.
SkyMap can also display photographic images, supplied in the form
of GIF or Windows bitmap files. Thousands of such images are
freely available on bulletin boards and commercial information
systems such as CompuServe and BIX. This allows you to build up
your own personal library of astronomical photographs which,
coupled with the map displays, really helps to bring the sky to
life!
There are a number of planetarium programs available today.
Unlike some of these, SkyMap makes no claims of blinding
calculation speeds. Instead, what SkyMap concentrates on is
accuracy. When writing SkyMap I've used the most accurate
methods available to me for all the calculations. This accuracy
makes SkyMap equally suited for both the novice astronomer who
just wants to know "what's that bright object up there?" and the
serious amateur or professional astronomer who wants a detailed
"finder chart" for a faint galaxy. Appendix A of this manual
describes the data sources SkyMap uses, and gives an indication
of the likely errors in its calculations.
SkyMap carries out its calculations in as efficient as manner as
possible, but it never compromises accuracy for the sake of
speed. An increase in speed can always be achieved by using a
faster computer! Having said all that, the speed is still
reasonable; on the author's 33MHz 486-based PC for example, the
horizon map, with default settings, is computed and drawn in
about 5 seconds.
Although I am releasing SkyMap as Shareware, I quite appreciate
that you may not consider it worth paying any money for in its
current form. I would obviously like to be paid the registration
fee - I've put a great deal of work into this software - but I
would still appreciate receiving your feedback on the program
even if you feel it's not currently worth registering. If you do
feel this way I'd like to know what, if anything, I could do to
make you change your mind in the future!
1
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Whilst developing SkyMap I've received the help and encouragement
of a number of people. I'd especially like to thank David Webber
for many useful suggestions and help with the mathematical
problems I encountered, and Steve Moshier for generously
consenting to allow me to use many of his coding ideas for
various astronomical calculations. Finally, I'd like to thank
Jean Meeus for writing the book "Astronomical Algorithms"
(Willman-Bell, 1991), without which this program would never have
existed.
What is Shareware? What is Shareware? What is Shareware?
Shareware distribution gives users a chance to try software
before buying it. If you try a shareware program and continue
using it, you are expected to register. Individual programs
differ on details -- some request registration while others
require it, some specify a maximum trial period. With
registration, you get anything from the simple right to continue
using the software to an updated program with printed manual.
Copyright laws apply to both Shareware and commercial software,
and the copyright holder retains all rights, with a few specific
exceptions as stated below. Shareware authors are accomplished
programmers, just like commercial authors, and the programs are
of comparable quality. (In both cases, there are good programs
and bad ones!) The main difference is in the method of
distribution. The author specifically grants the right to copy
and distribute the software, either to all and sundry or to a
specific group. For example, some authors require written
permission before a commercial disk vendor may copy their
Shareware.
Shareware is a distribution method, not a type of software. You
should find software that suits your needs and pocketbook,
whether it's commercial or Shareware. The Shareware system makes
fitting your needs easier, because you can try before you buy.
And because the overhead is low, prices are low also. Shareware
has the ultimate money-back guarantee -- if you don't use the
product, you don't pay for it.
Disclaimer Agreement Disclaimer Agreement Disclaimer Agreement
Users of SkyMap must accept this disclaimer of warranty:
"SkyMap is supplied as is. The author disclaims all warranties,
expressed or implied, including, without limitation, the
warranties of merchantability and of fitness for any purpose. The
author assumes no liability for damages, direct or consequential,
which may result from the use of SkyMap."
2
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
SkyMap is a "shareware program" and is provided at no charge to
the user for evaluation. Feel free to share it with your
friends, but please do not give it away altered or as part of
another system. The essence of "user-supported" software is to
provide personal computer users with quality software without
high prices, and yet to provide incentive for programmers to
continue to develop new products. If you find this program
useful and find that you are using SkyMap and continue to use
SkyMap after a reasonable trial period, you must make a
registration payment to Chris Marriott. The registration fee
will license one copy for use on any one computer at any one
time. You must treat this software just like a book. An example
is that this software may be used by any number of people and may
be freely moved from one computer location to another, so long as
there is no possibility of it being used at one location while
it's being used at another. Just as a book cannot be read by two
different persons at the same time.
Commercial users of SkyMap must register and pay for their copies
of SkyMap within 30 days of first use or their license is
withdrawn. Site-License arrangements may be made by contacting
Chris Marriott.
Anyone distributing SkyMap for any kind of remuneration must
first contact Chris Marriott at the address below for
authorisation. This authorisation will be automatically granted
to distributors recognised by the ASP as adhering to its
guidelines for shareware distributors, and such distributors may
begin offering SkyMap immediately (However Chris Marriott must
still be advised so that the distributor can be kept up-to-date
with the latest version of SkyMap.).
You are encouraged to pass a copy of SkyMap along to your friends
for evaluation. Please encourage them to register their copy if
they find that they can use it.
ASP Ombudsman Statement ASP Ombudsman Statement ASP Ombudsman Statement
This program is produced by a member of the Association of
Shareware Professionals (ASP). ASP wants to make sure that the
shareware principle works for you. If you are unable to resolve a
shareware-related problem with an ASP member by contacting the
member directly, ASP may be able to help. The ASP Ombudsman can
help you resolve a dispute or problem with an ASP member, but
does not provide technical support for members' products. Please
write to the ASP Ombudsman at 545 Grover Road, Muskegon, MI 49442
or send a CompuServe message via CompuServe Mail to ASP Ombudsman
70007,3536.
Contacting the Author Contacting the Author Contacting the Author
3
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
If you have any questions about SkyMap, or you require support,
you can contact me in a number of different ways:
1. If you have the capability, e-mail is the best way to contact
me. It's quick, and a written request is always easiest to deal
with. I can be reached at any of the following addresses, in no
particular order of preference:
Internet: chris@chrism.demon.co.uk
CompuServe: 100113,1140
2. If you prefer to write me a letter, my postal address is:
Chris Marriott
9, Severn Road
Culcheth
Cheshire WA3 5ED
United Kingdom
I have no intention of moving, so that address should apply for
the foreseeable future! Note that this is also the address to
which registration fees should be sent.
3. Finally, if you would like to speak to me in person, you can
telephone me on the following number:
Within the UK: 0925 76 4131
International: +44 925 76 4131
Please call at the weekend, or between 6pm and 10pm GMT during
the week. Please also remember that I am in the UK, and consider
the time difference if you're calling from overseas. I would not
welcome a call at 3am if you happen to be on the west coast of
the USA and you decide to phone me at 7pm local time!
Please feel free to contact me - I'd love to receive any comments
you may have on the program, or suggestions as to how it could be
improved.
Registering SkyMap Registering SkyMap Registering SkyMap
As described above, SkyMap is not free software. It is shareware
and, as such, you must register it if you find it useful after a
reasonable trial period. I would suggest that 30 days is
reasonable for such a trial. The shareware concept is based on
trust, and I trust you to pay for this program if you are using
it. There are several different levels of registration
available:
Personal: Personal registration allows the program to be used by
one person. You may install the software on any number of
computers, as long as only one will be in use at any one time.
4
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Club: Club registration allows free use by all members of an
astronomy club (or, indeed, any other sort of club!), on any
number of computers, whilst at club meetings. Any club member
who wants to use the program at home is still expected to
register the program personally.
Educational: Educational registration allows unrestricted
copying and use of SkyMap within a school, college, university,
or other educational establishment.
Corporate??: Frankly, I can't imagine any corporate use for
SkyMap, but if you are a corporate user and you'd like to
negotiate a site license for use of SkyMap, please contact me to
discuss it!
For full information about registration, including details of
current prices and methods of payment, please refer to the
separate registration form "REGISTER.TXT".
If you have access to CompuServe you may wish to take advantage
of the on-line shareware registration facilities available to
quickly and easily obtain a personal registration for SkyMap. To
do so, enter the command "GO SWREG" at any "!" prompt, and select
program ID 876. The registration fee will be charged directly to
your CompuServe account and, especially if you live in a country
other than the UK, you will avoid the inconveniences caused by
having to deal with foreign currency.
In return for registering SkyMap you will receive:
1. A registered copy of the latest version of SkyMap, with the
registration reminder removed from the "About SkyMap" box.
2. A bound, illustrated manual.
3. A much larger star database.
4. Unlimited lifetime support, using any of the methods
described in the "Contacting the Author" section of this manual.
5. The right to purchase, for a small fee, additional materials
which enhance the use of SkyMap.
6. The right to upgrade to a registered copy of the latest
version of SkyMap, at any time, for a nominal fee. You may do
this as often as you wish.
7. A lifetime money-back guarantee. If you ever find a serious
bug in SkyMap which makes it unusable, your registration fee will
be immediately refunded, with no questions asked.
5
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
System Requirements System Requirements System Requirements
SkyMap requires Microsoft Windows version 3.1 or above to run.
It will not work with Windows 3.0 or earlier. Windows 3.0 had a
number of major flaws, and early on in the development of SkyMap
I made the decision not to support it. I apologise if this
inconveniences you, but supporting Windows 3.0 would have quite
severely restricted certain aspects of SkyMap's operation.
You do not actually need a maths coprocessor to run SkyMap, but
it will run very slowly without one. SkyMap does a great deal a
great deal of trigonometry while creating maps, and use of a
coprocessor can speed up this process by a factor of ten or more!
SkyMap will work with any type of video card supported by
Windows. For best results, VGA or better is recommended. If you
want to display photographic images you really need a card and
monitor capable of displaying 256 (or more) colours at the same
time, such as a "SuperVGA", "High Colour" or "True Colour" video
card..
Maps can be printed, in either black and white or colour, on any
type of printer supported by Windows. The best results will be
obtained from a laser or high-quality ink-jet printer, but
perfectly acceptable results will be obtained from a 9-pin or 24-
pin dot-matrix printer, too.
The files distributed with SkyMap require a total of about 1.4MB
of disk space.
6
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Setting Up SkyMap Setting Up SkyMap Setting Up SkyMap
Before SkyMap can be used, it must be installed on your computer,
then configured to know about your location and time zone.
Installing the Software Installing the Software Installing the Software
SkyMap is distributed as three ZIP archive files - one containing
the program and documentation; one containing the support files
essential to the program's operation, and the third containing
optional files which enhance the program but are not essential.
The program archive, which will probably be called "SKYMP13A.ZIP"
should contain the following files:
README.1ST Read this file!
REGISTER.TXT Registration information
HISTORY.TXT SkyMap release history
SKYMAP.EXE The SkyMap program
SKYMAP.HLP On-line help file
SKYMAP.TXT This manual
CTL3D.DLL 3D control library
MWSPIN.DLL Spin button control library
MSDNTB.DLL ToolBar library
The data and support archive, which will probably be called
"SKYMP13B.ZIP", should contain the following files:
README.2ND Read this file!
STAR.SKY Main star database
STARNAME.SKY Star name database
STARPROP.SKY Star proper name database
CONFIGUR.SKY Constellation figures database
CONNAME.SKY Constellation name database
MOON.SKY Moon position database
PLANETS.SKY Planet position database
The optional files archive, which will probably be called
"SKYMP13C.ZIP", should contain the following files:
README.3RD Read this file!
CONOUTLN.SKY Constellation boundaries database
RNGC.SKY RNGC non-stellar object database
RNGCPOP.SKY RNGC object popular name database
You may also have one or more picture file archives. Please
refer to the "Displaying Pictures" section of the manual for
information about how to use these.
To install SkyMap, carry out the following steps:
7
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
1. Create a directory on your hard disk. For the purposes of
this discussion we'll assume you want to install the program in
directory SKYMAP on your C: drive. Enter the commands:
C:
MD \SKYMAP
2. Unpack both the archive files into the directory. Assuming
that the archives are on a floppy disk in the A: drive you would
do this with the commands:
CD \SKYMAP
PKUNZIP A:\SKYMP13A
PKUNZIP A:\SKYMP13B
PKUNZIP A:\SKYMP13C
3. Read the "Readme" text files. They may contain important
additions to the information in this manual!
4. Select the Program Manager group you'd like to add the SkyMap
icon into.
5. From the Program Manager's "File" menu, select "New...". A
dialog box will appear. Select "Program Item" (this should be
the default, anyway) and press the OK button.
6. The "Program Item Properties" dialog will appear. Fill it in
as shown below, then press the <OK> button.
Description: SkyMap
Command Line: SKYMAP.EXE
Working Directory: C:\SKYMAP
The SkyMap icon (a picture of a telescope) should appear in the
Program Manager group window. SkyMap is now installed and ready
to run.
Configuring SkyMap for your Location Configuring SkyMap for your Location Configuring SkyMap for your Location
When SkyMap is run for the first time, you must configure it for
the your location. Before SkyMap can correctly draw a map of the
sky for you, you have to tell it where you are, and what time
zone you are in. To configure the program, carry out the
following steps:
1. Run SkyMap by double clicking on its icon in the Program
Manager. The empty SkyMap main window should appear. Note the
grey "status bar" at the bottom of the window. This is used to
display important information to the user, so keep an eye on it!
2. From the File menu, choose "New...". The "Create New Window"
dialog box will appear, which lists the different types of window
you can create. Press <Enter> to create a Horizon Map window,
8
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
which will be the default. A blank Horizon Map window will
appear, and additional items will be added to the menu bar. Note
that the message "Press F5 to draw the map" has appeared on the
status bar. Ignore this message for the time being!
3. From the "Options" menu, choose "Observer...". The
"Observer" dialog box will be displayed. This is where you set
up all the information about the location you will be observing
from.
Fill in your longitude and latitude, each in degrees, minutes,
and seconds. You need not be exact - a position correct to the
nearest degree is fine unless extreme accuracy is required.
In the "Local Time" box enter your time zone, expressed in
minutes ahead or behind Universal Time (UT), commonly called
Greenwich Mean Time (GMT). Eg, if your time zone is Eastern
Standard Time, you are 5 hours behind UT, so you would enter
"300" (5x60) into the text box, and click the button to change
the display to read "minutes behind UT".
If Daylight Saving Time (called "Summer Time" in the UK) is
currently in operation, check the appropriate box. If it is not
currently in force, leave the box blank. If the box is checked,
your local time is taken to be an extra hour ahead of UT.
4. Finally, you should save the information you've entered.
From the "File" menu, choose "Save Defaults...". A box will
appear asking you if you really want to save the information.
Press the "Yes" button, or just press <Enter> to save the
information. All the current map settings will be saved in a
configuration file called SKYMAP.INI and will be used as the
default values for all horizon maps subsequently drawn.
5. Press the <F5> key. A "Please wait" box will be displayed
for a few seconds (depending on the speed of your computer),
after which a map of the southern part of the sky as it currently
looks from your location will appear in the map window.
Congratulations - you have successfully drawn your first map!
Note the following features of the map:
1. The "status bar" at the bottom of the window displays
information about the map, such as the time and date, and the
coordinates of the map centre.
2. The "Toolbar" at the top of the window provides a shortcut
method of accessing many of the most frequently used commands, as
well as giving an instant view of which map features are
currently enabled.
3. Along the bottom of the map is the horizon, with the compass
points displayed along it. By default, the program displays a
view of roughly one third of the sky, centred on the southern
9
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
horizon. The zenith (the point directly overhead) is at the top
of the map.
4. Stars are displayed as dots of differing sizes. The brighter
the star, the larger the dot. By default, stars down to
magnitude 5.0 are displayed, although the star database supplied
with the program contains stars down to magnitude 7.0. (The
complete SAO catalog is reasonably complete down to about
magnitude 9.5.)
5. By default, constellation names and figures are displayed.
These can both be switched off using the items on the "View"
menu, or by clicking on the appropriate buttons on the Toolbar.
6. Planets are shown as dots, with the standard astronomical
symbol alongside. The Moon is displayed with its correct phase
and orientation. The Sun is displayed as a hollow circle.
10
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Horizon Maps Horizon Maps Horizon Maps
A horizon map shows the sky as seen from the observer's location
for a particular time and date. It will probably be the starting
point for most runs of SkyMap.
Drawing a Horizon Map Drawing a Horizon Map Drawing a Horizon Map
To draw a horizon map, the following steps should be followed:
1. From the "File" menu, choose "New...". The "Create New
Window" dialog box will be displayed, showing the different types
of window that can be created. "Horizon Map" should be the
default selection in the list, so simply press <Enter> to create
a new Horizon Map window.
2. Use the items on the "Options" menu to set all the options
required for the map. These options are described below. Once
the options have been set, you can save them to be used as the
defaults for all future Horizon maps by selecting the "Save
Defaults..." option from the "File" menu.
3. Use the items on the "View" menu to select which features you
would like plotted on the map. Most of these can also be
selected from the Toolbar, too.
4. Press the <F5> key to draw the map. This process will take
anything from a few seconds to (in extreme cases!) several
minutes, depending on the speed of your computer, and the
complexity of the map.
5. When the map appears, you can zoom in or out on it, identify
objects on it, or print it. These options are described later.
Horizon Map Options Horizon Map Options Horizon Map Options
Viewpoint
This option allows you to determine which part of the sky appear
on the map. When this option is selected, the "Horizon View"
dialog is displayed.
The "Azimuth" and "Altitude" fields specify the coordinates of
the centre of the map. The azimuth corresponds to the compass
direction you are looking in and has the value 0. for due North,
90. for East, 180. for South, and 270. for West. The altitude
indicates how far up you are looking, and is 0. on the horizon,
and 90. directly overhead.
The "Radius" field specifies the vertical size of the map. The
minimum altitude displayed on the map will be "Radius" degrees
below the centre; the maximum altitude will be "Radius" degrees
11
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
above the centre (ie, the range of altitude displayed on the map
will be double the value entered). The azimuth range of the map
is scaled automatically.
Notes:
1. Even if the radius is greater than the centre azimuth (ie,
Centre-Radius<0), objects below the horizon will not be displayed
- the horizon line will simply appear higher up the map.
2. To display a circular map of the whole sky, enter a centre
altitude of 90., and a radius of 90.. In this case the azimuth
setting simply determines the orientation of the map - the
specified azimuth will be appear at the bottom of the map.
Time
The time and date for which the map is drawn are initially set
from the computer's clock for the instant that the Horizon Map
window is created. The Time option allows the user to display a
map for any other time and date. When this option is selected,
the "Observation Time" dialog is displayed.
Fill in the dialog fields for the time and date required.
Pressing the "Now" button will read the time and date from the
computer's clock.
Notes:
1. Dates before 1AD should be entered as negative numbers in the
normal astronomical manner. Enter the year 1BC as "0", 1000BC as
"-999", and so on.
2. Dates must be between 4000BC (-3999) and 8000AD, this being
the range over which the program's calculations are valid.
3. Dates on or after 0h on 15th October 1582 are assumed to be
in the Gregorian calendar; dates before then in the Julian
calendar.
4. The observation time is assumed to be a local time - ie, the
time as shown on an observer's clock. The time zone information
specified on the Observation Location dialog (see below) is used
to convert the time to UT.
Observer
The Observer option allows the user to enter information about
the location from which the observation is taking place. When
this option is selected, the "Observer" dialog is displayed.
The "Latitude" and "Longitude" fields specify the location of the
observer. Both are entered in degrees, minutes, and seconds
12
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
although, unless extreme accuracy is required, a position correct
to the nearest degree will normally suffice.
The "Conditions" information describes the atmospheric
temperature and pressure at the time of observation. This
information is used when calculating the effects of refraction.
Changing these values only has a very small effect and, unless
extreme accuracy is desired, they may safely be left at their
default values.
The "Local Time" data specifies the observer's time zone. It is
used to convert the time of observation (which is always assumed
to be local time) into UT or GMT. The time difference is entered
in minutes (not hours!) difference between local time and UT.
For example, an observer on the east coast of the USA, whose
clocks are set 5 hours earlier than GMT, should enter "300" (5 x
60) in this box, and click the arrow to change the text to
"before UT".
The "Daylight saving time" box should be checked if DST (called
"Summer Time" in the UK, and perhaps other countries too) is
currently in operation. If the box is checked, the local time is
assumed to be one additional hour ahead of UT.
Notes:
1. The reason that the time difference is entered in minutes,
rather than hours, is that not all countries are exact hours
ahead of or behind GMT. India, for example, is 5.5 hours (330
minutes) ahead of GMT.
Stars
The Stars option controls both which stars are plotted on the
map, and the way that plotted stars are displayed. When this
option is selected, the "Star Display" dialog is displayed.
The "Limiting magnitude of map" field determines the magnitude of
the faintest star whose position will be calculated. The higher
the number, the fainter the stars which will be displayed (and
the longer the map will take to compute). The star database
supplied with the program contains stars down to magnitude 7.0;
the full SAO star catalog has stars down to magnitude 9.5 or so.
The "Limiting magnitude displayed" field determines the magnitude
of the faintest star that will actually be displayed on the map.
Once a map has been drawn, you can change the value in this field
to temporarily suppress the display of the fainter stars on a
map, to remove "clutter". The value entered in this field should
be less than or equal to the value entered in the "Limiting
magnitude" field above..
The lower half of the dialog box controls the way that the size
of the star images varies with their magnitude. All stars
13
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
brighter than the first "Display mag" field will be displayed
using the size of star circle shown to its right. All stars
fainter than the second "Display mag" field will be displayed
using the size of star circle shown to its right. All stars with
magnitudes between these two limits will be drawn with an image
size inversely proportional to the magnitude (ie, the brighter
the star, the larger the image).
Notes:
1. The number of stars rises very quickly with magnitude.
Generally, increasing the limiting magnitude by one magnitude
will more than double the number of stars visible on the map, and
consequently the time taken to compute their positions.
Star Labels
This option controls the way in which stars are labelled on the
map. When selected, the "Star Labels" dialog box is displayed.
The way in which stars are named has evolved over hundreds of
years. As a result, a lot of the brighter stars have many
different names. The "Label Preferences" box allows the user to
determine which, if any, of those names is displayed on the map.
"Proper Names" refers to the "popular" name of a star, such as
"Polaris" or "Rigel".
"Bayer Letters" refers to the convention of labelling the
brightest stars in each constellation with Greek letters, such as
"Alpha Centauri" or "Beta Cygni".
"Flamsteed Numbers" refers to the convention of labelling stars
in each constellation with numbers, such as "61 Cygni".
The "Label Options" box at the bottom of the dialog box
determines which stars are labelled. If "All stars" is selected,
then all stars which have the appropriate name will be labelled.
If "Brighter than magnitude" is selected, then only those stars
brighter than the number in the edit box will be labelled.
Notes:
1. This dialog only determines the way in which stars are
labelled. If order to actually display star labels, the "Star
Labels" option must be enabled on the "View" menu or the Toolbar.
2. If a star has multiple names, and more than one of the naming
options is selected in the "Preferences" box, the name highest up
the box will be displayed. Eg, if both the "Proper Names" and
"Bayer Letters" options are selected, the map would display the
name "Polaris" in preference to "Alpha Ursae Minoris" when
labelling the pole star.
Labels
14
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Selecting this option displays a submenu of labelling options.
If the "Altitude" option is selected, the "Altitude Label
Options" dialog box is displayed.
The "Label type" radio buttons allow the type of altitude
labelling to be selected. The options are:
Automatic The label interval is selected automatically.
Every ... The label interval is specified in the text box.
Nothing No altitude labels are displayed.
If the "Draw Altitude Lines" box is checked, altitude lines are
drawn across the map at the appropriate (manual or automatic)
intervals, and the lines are labelled at the left-hand side of
the map.
If the box is blank, altitude tick marks are drawn in the centre
of the map.
Notes:
1. If the "Nothing" box is selected, neither altitude lines nor
labels are drawn, regardless of the state of the "Draw Altitude
Lines" check box.
Selecting the "Azimuth" option from the "Labels" submenu displays
the "Azimuth Label Options" dialog box.
The radio buttons in the "Label with" box control the type of
azimuth labelling, and determine which (if any) of the other
values in the dialog are used.
If the "Compass Points" button is selected, the horizon is
labelled with the names of compass points, and the options in the
"Compass Interval" section of the dialog are used.
If the "Azimuth" button is selected, the horizon is labelled with
azimuth numbers (in degrees), and the options in the "Azimuth
Interval" section of the dialog are used.
If the "Nothing" button is selected, the azimuth axis is not
labelled, and the rest of the dialog is ignored.
The "Compass Interval" section of the dialog determines the
labelling method used when "Compass Point" labelling is selected.
The radio buttons allow the labelling interval to either be
determined automatically, or one of three manual intervals
selected.
The "Azimuth Interval" section of the dialog determines the
labelling method used when "Azimuth" labelling is selected. The
options allow the labelling interval to be either determined
15
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
automatically, or specified manually by the value in the text
field.
If the "Draw Azimuth Lines" box is checked, lines are drawn up
from the labelled points on the horizon to the top of the map.
Notes:
1. Azimuth lines are always labelled on the horizon line. If
the horizon line is not visible on the map, you will not see any
labels!
Constellation Names
This option allows the user to choose the font used for
constellation names. Selecting this option displays a standard
font selection dialog.
RNGC Objects
Selecting this option displays the "RNGC Options" dialog box,
allowing you to determine which deep sky objects are displayed on
the map.
The "Object Selection" box determines which catalogue will be
searched to find objects to display; the entire RNGC catalogue or
only Messier objects.
The "Object Types" box controls which objects will be displayed
on the map, based on their type. If the "All objects" box is
checked, then the other boxes in the group are ignored, and all
objects which match the other selection criteria will be
displayed. If the "All objects" box is not checked, individual
types of object can be selected using the other boxes in this
group.
The "Magnitude Limit" box allows you to control which objects are
displayed, based on a magnitude selection. If "All Objects" is
selected, then all objects matching the other selection
parameters will be displayed; if "Brighter than mag" is selected,
then only those objects brighter than the specified magnitude
will be displayed.
Finally, the "Label Objects" box, determines whether displayed
objects will be labelled. If the box is checked, objects will be
labelled. Messier objects will be labelled "M" followed by a
number (eg "M32"); other objects will simply have their RNGC
catalogue number displayed (eg "1985" refers to the planetary
nebula "RNGC 1985" ).
Notes:
16
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
1. This is a complex dialog box - the most complex in the
program! - but it gives you the ability to exercise very fine
control over the non-stellar objects which are displayed. For
example, you can make selections such as "only display globular
clusters in the Messier catalogue brighter than magnitude 11".
2. The program will only display those Messier objects that are
in the RNGC. Four objects in the Messier catalogue are not in
the RNGC, so will not be drawn. These are: M24 (a local
brightening of the Milky Way), M25 (the open cluster IC 4725),
M40 (the wide double star Winneke 4), and M45 (the Pleiades).
3. The RNGC is based on the NGC, compiled towards the end of the
19th century. As such, it contains many incorrect
classifications, based on the information available at the time.
For example, the Crab Nebula in Taurus, M1, we now know to be a
supernova remnant, but the RNGC classifies it as a planetary
nebula. The RNGC is, however, a catalogue of great historical
significance, and no attempt has been made by the author to
"correct" it.
4. The symbols used to draw non-stellar objects on the map have
been based on those used in the authoritative "Uranometria 2000"
star atlas.
Colours
This option displays a sub-menu allowing the user to select the
colours used for every item drawn on the map for either the
screen or the printer. When either "Screen" or "Printer" is
selected, the "Horizon Map Colours" dialog box is displayed.
To view or edit the colour of any map component, either double
click on the name in the listbox, or move the listbox highlight
to the name and press the "Edit..." button. Either way, a
standard colour selector box will be displayed, letting you
choose the colour for the item.
Notes:
1. Pressing the "Cancel" button will restore ___ all the colours to
their previous settings, not only the colour just edited.
2. The "Printer" colour settings only relate to the printing of
colour maps. Refer to the printing section of the manual for
further information.
Reduce Positions
This item is a "toggle switch", controlling whether position
reductions are applied to objects displayed on the horizon map.
17
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
If this option is ticked, the positions of all objects are
rigorously corrected for the effects of precession, nutation,
aberration, parallax, and refraction. If this option is not
ticked, only the corrections for refraction and (for planets)
diurnal parallax are applied.
The purpose of this toggle is to speed up map display, especially
on slow computers. Unless very high accuracy is required, this
option can safely be switched off for maps drawn for the time
period 1950 - 2050. Outside this period, the effects of
precession start to become significant, and the option should
always be switched on.
Draw
Selecting this option will draw the map, using the current option
settings. You may press the <F5> function key as a "shortcut"
for this option.
Using the Horizon Map Using the Horizon Map Using the Horizon Map
Once the horizon map has been created using the methods described
in the previous section of the manual, it can be manipulated in
various way. This section describes the available options:
Setting the Visibility of Objects
The first section of the "View" menu contains a list of item
names, each of which has a tick alongside if that type of item is
currently visible. The items are:
Stars
Star Labels
Planets
Constellation Figures
Constellation Boundaries
Constellation Names
Alt/Az Grid
RNGC Objects
Each of these items has a corresponding button on the ToolBar.
To change an item from visible to invisible, or vice versa,
either select the item from the menu, or press the button on the
ToolBar.
Changing the map scale
The "Zoom In" and "Zoom Out" items on the "View" menu may be used
to change the magnification of the map. The <F2> and <F3>
function keys are shortcuts for these operations, as are the
first two buttons on the ToolBar. When the map is first drawn,
18
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
it is scaled so that the map exactly fills a maximised map
window. Every time "Zoom In" is selected, the size of the map
increases by 50%, and the map is redrawn. Every time "Zoom Out"
is selected, the size is correspondingly reduced.
When the map is zoomed, the centre of the current window will
remain stationary. You can therefore zoom in a particular
feature by first scrolling it to the centre of the window, then
repeatedly pressing the <F2> key. To aid this process, a
shortcut method has been provided to bring a point to the centre:
1. Position the mouse pointer over the point on the map you
would like to bring to the centre.
2. Press the right mouse button. A pop-up menu will appear
under the mouse pointer.
3. Select the "Centre" item with the left mouse button. The
window will scroll to bring the chosen point to the centre of the
map.
Note that the map will not scroll past its edges (the boundaries
of the full-screen normal size map). In order to bring a point
to the centre of the map it may, therefore, be necessary to zoom
in one or more times first.
Identifying Objects on the Map
To display information about any object visible on the map, move
the mouse pointer over the object, and press the right mouse
button. A pop-up menu will appear. Select the item you wish to
identify. A dialog box will appear displaying information about
the object.
Stars:
If you ask for information about a star, a "Star Information"
dialog box is displayed. The amount of information displayed
will depend on the star, but will include the following:
1. The star's SAO catalogue number is displayed in the dialog
box title. The SAO number is the way that SkyMap identifies the
star internally - all other information is derived from this.
2. The top section of the dialog displays the identify of the
star. The same star can be identified in a truly bewildering
variety of different ways. SkyMap attempts to show a few of the
more popular names for the star:
The first line of the dialog always displays the name of the
constellation that the star is in. In the case of a star which
has either a Bayer letter or Flamsteed number, the star's
constellation is actually stored in the database. In cases where
19
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
this information is not present, the constellation is computed
from the star's position, using the official IAU constellation
boundaries.
The next line, if present, displays the "proper name" of the star
- "Rigel", for example. Note that many star names are derived
from Arabic and, as such, have a number of alternate English
spellings. In the case of such stars, the name that SkyMap
displays may well be slightly different from the name your
reference sources show. All that means is that I used a
different reference book!
Next are shown the star's Bayer letter (eg beta Orionis) and
Flamsteed number (19 Orionis), if present.
Finally in the initial section of the dialog, the star's visual
magnitude is shown.
3. The lower section of the dialog shows the position of the
star in several different coordinate systems.
First, the star's apparent geocentric right ascension and
declination are displayed. These coordinates are referred to the
true equinox and ecliptic of date, and are corrected for:
Proper Motion
Annual Aberration
Precession
Nutation
The star's position is also corrected for refraction before being
displayed on the map, but the apparent position displayed in the
dialog box does not include this correction. Note that rigorous
position corrections are applied, regardless of the current
setting of the "Reduce Positions" switch on the "Options" menu.
Next, the star's catalogue position is displayed - the right
ascension (RA) and declination for the mean equinox and ecliptic
of epoch J2000.0. This information is taken straight from the
SAO star catalogue and contains no position corrections.
Finally, the current altitude and azimuth as seen from the
observer's location are displayed. The altitude displayed here
includes the effects of refraction.
Planets:
If information about a planet is requested, a more complex dialog
with multiple screens of information is displayed. The dialog
has buttons down the right hand side for switching between the
different screens of information. The names on the buttons refer
to the position of the viewer - eg, the "Sun" button displays a
screen of heliocentric information.
20
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
The information displayed is as follows:
The "Local" screen displays information about the planet as seen
from the observer's location at the time and date for which the
map is displayed. The following information is displayed:
1. The altitude and azimuth of the planet as seen from the
observer's location at the current time. This is derived from
the apparent geocentric position, with additional corrections
being applied for diurnal parallax (the difference between the
position of the planet as seen from the centre of the Earth and
the position as seen from the observer's actual position) and
refraction.
The "Earth" screen (initially displayed) displays information
about the planet as seen from the centre of the earth - ie,
geocentric information. The following information is displayed:
1. The apparent geocentric right ascension and declination,
referred to the true equinox and ecliptic of date. This position
is corrected for the effects of:
Light Time
Light Deflection (due to the Sun's gravity)
Annual Aberration
Nutation
The position of the planet as displayed on the map has additional
corrections for diurnal parallax and refraction, but these
corrections are not reflected in the position displayed here.
2. The constellation the planet is in.
3. The true (geometric) distance of the planet in both
astronomical units (exactly) and millions of km (approximately).
In the case of the Moon, the exact distance is displayed in km.
The "Sun" screen displays information about the planet as seen
from the centre of the Sun - ie, heliocentric data. The
following information is displayed:
1. The apparent ecliptic longitude and latitude of the planet,
referred to the true ecliptic of date.
2. The geometric radius vector of the planet (ie, the distance
between the planet and the Sun) in both astronomical units
(exactly) and millions of km (approximately).
The "Physical" screen displays physical information about the
planet. The following information is displayed:
21
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
1. The visual magnitude.
2. The phase, as a fraction between 0 and 1. A phase of 0
indicates that the object is "new"; a phase of 1 is "full". The
phase is equal to the fraction of the planet's disk that is
illuminated, as seen from the Earth.
3. The apparent diameter, in seconds of arc. For some planets,
separate equatorial and polar diameters are shown.
4. The phase angle, in degrees. This is the angle between the
Earth and Sun, as seen from the centre of the planet, and
determines the phase of the planet as seen from the Earth.
5. The elongation, in degrees. This is the angle between the
planet and the Sun, as seen from the centre of the Earth.
6. The light time in hours, minutes, and seconds. This is the
time taken for light to travel from the planet to the observer,
and is an indication of the "age" of the view we see of the
planet. Eg, if the light travel time for Mars is shown as 5
minutes, this means that we are seeing Mars as it actually was 5
minutes ago.
RNGC Objects:
If you ask for information about an RNGC object, a dialog box is
displayed. The amount of information displayed will depend on
the object, but will include the following:
1. The dialog box title will contain the catalogue number of the
object. This will be shown as a Messier number for objects in
the Messier catalogue, and an RNGC catalogue number otherwise.
2. The upper section of the dialog identifies and describes the
object. The following information could be displayed:
RNGC Number: For Messier objects, the corresponding number in
the RNGC catalogue. For example, in the case of "M44", this line
will display "NGC 2632".
Popular name: Some objects have a "popular name" by which they
are commonly known, in addition to their various catalogue
numbers. For example, in the case of M44, this line will display
the name "Praesepe".
Type of object: A brief description of the object type, such as
"Galaxy", "Globular Cluster", "Diffuse Nebula", etc. As has
already been stated, these classifications are not always
correct, and should not be taken as an authoritative guide to
what an object really is! That having been said, the
classification is correct for the vast majority of objects.
22
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Magnitude: The visual magnitude of the object. It should be
noted that this is normally an "integrated magnitude" - the total
amount of light received from the whole of the object. Normally,
a 10th magnitude galaxy is visually a lot fainter than a 10th
magnitude star, because in the case of the galaxy the light is
coming from an area of sky, rather than from a point source.
Description: The "Dreyer Description" of the object. When
Dreyer compiled the NGC in 1888, he gave a brief visual
description of the object in a highly compressed format. These
descriptions are, in the author's opinion, the real value of the
NGC, since they indicate what you are likely to actually see in a
typical modern amateur telescope. The "encoded" format of the
descriptions may seem cryptic and hard to understand at first
but, with practice, soon becomes a useful source of information.
Refer to Appendix B of the manual for a description of Dreyer
descriptions.
3. The lower section of the dialog shows the position of the
object in several different coordinate systems.
The first line displays the name of the constellation the object
is in.
The second line shows the object's apparent geocentric right
ascension and declination, referred to the true equinox and
ecliptic of date. The position is corrected for:
Annual Aberration
Precession
Nutation
The object's position is also corrected for refraction before
being displayed on the map, but the apparent position displayed
in the dialog box does not include this correction. Note that
rigorous position corrections are applied, regardless of the
current setting of the "Reduce Positions" switch on the "Options"
menu.
Next, the object's catalogue position is displayed - the right
ascension (RA) and declination for the mean equinox and ecliptic
of epoch J2000.0. This information is taken straight from the
RNGC catalogue and contains no position corrections.
Finally, the current altitude and azimuth as seen from the
observer's location are displayed. The altitude displayed here
includes the effects of refraction.
Zooming to an Area Map
If you wish to display a detailed "Area Map" of a particular
region of the sky, position the mouse pointer over the point on
the horizon map that you wish to be the centre of the area map.
23
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Press the right mouse button and select "Area Map..." from the
pop-up menu. The "Sky Area View" dialog box will appear, with
the coordinates of the map centre already filled in. Enter the
radius of the map you would like, in degrees, then press <Enter>.
A blank area map window will appear. The next chapter of the
manual describes how to draw and use the Sky Area map.
Printing the Map
To print the map, choose the "Print" option from the "File" menu.
This will display the "Print Options" dialog box.
The "View Options" box selects what type of map is drawn. If
"Whole Map" is selected, the entire map will be drawn, scaled to
fit onto the printer page. If "Current View" is selected, the
current map view will be printed, at the current zoom factor.
The "Colour Options" box is used to select whether the map is
printed in black and white or colour. If "black and white" is
selected, all objects on the map are printed black, and the map
background is left white. If "Colour" is selected, the map
background is again left white, but the colour of all other
objects is taken from the settings in the
"Options/Colour/Printer" dialog.
When the <OK> button is pressed, a standard "Print" dialog is
displayed. This allows you to select the printer, resolution,
paper orientation etc in the normal way. Press <OK> from this
dialog to print the map.
Notes:
1. By default, the map is printed in landscape orientation. If
you wish to change this, use the "Print Setup" option.
2. The default "Print Options" settings of "Whole Map" and
"Black and White" correspond to the way that maps were printed in
previous versions of SkyMap.
3. The "Current View" printout is intended as a "quick and
dirty" method of getting a printed map of a zoomed-in area of the
sky, without having to draw a separate Sky Area map and print
that. No attempt is made to properly scale the map to fit the
paper size, draw borders, or anything else. If you have a very
high zoom factor set, and try to print to a high-resolution
device using this settings, problems may occur.
4. The "Colour" setting in the "Colour Options" box can be used
to print a grey-scale map even on a black and white printer. The
exact correspondence between colours and shades of grey will
depend on the capabilities of the printer driver. This works
beautifully on a PostScript laser printer; not so well on an
Epson 9-pin dot matrix printer!
24
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
25
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Sky Area Maps Sky Area Maps Sky Area Maps
A Sky Area map shows a detailed view of a (normally) small area
of the sky, centred on a particular point of right ascension and
declination. It is a circular map, displaying all objects within
a specified radius of the centre.
Drawing a Sky Area Map Drawing a Sky Area Map Drawing a Sky Area Map
There are two ways to draw a Sky Area map:
1. Draw a horizon map, then click the right mouse button over
the location you want to be the centre of the Sky Area map.
Select "Area Map..." from the pop-up menu which appears.
2. From the "File" menu, select "New...". The "Create New
Window" dialog box will appear. Select "Sky Area Map" from the
listbox and press <OK>.
Whichever of these two methods is used, the "Sky Area View"
dialog box will be displayed.
The "Vertical Radius" field specifies the radius of the map, in
degrees. This must be between 1. and 90.. The "Right Ascension"
and "Declination" fields specify the coordinates of the map
centre. If you are drawing the Area map from a Horizon map,
these will already contain the correct values.
When the dialog is correctly filled in, press <OK> to create a
new map. A blank Sky Area Map window will be displayed, and the
menu will change to the Sky Area menu.
Use the items on the "Options" menu to set all the options
required for the map. These options are described below. Once
the options have been set, you can save them to be used as the
defaults for all future Sky Area maps by selecting the "Save
Defaults..." option from the "File" menu.
Finally, press the <F5> key to draw the map. This process will
take anything from a few seconds to (in extreme cases!) several
minutes, depending on the speed of your computer, and the
complexity of the map.
Sky Area Map Options Sky Area Map Options Sky Area Map Options
Viewpoint
This option allows the user to specify which part of the sky is
visible on the map. When this option is selected, the "Sky Area
View" dialog is displayed.
26
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
The "Vertical Radius" field controls the radius of the map. It
can take values ranging from 1o to 90o. The total field of view
of the map will be double the value entered here.
The "Right Ascension" and "Declination fields specify the
coordinates of the centre of the map. Right Ascension is entered
in hours and minutes of time; declination in degrees and minutes
of arc.
Time
The time and date for which the map is drawn are initially set
from the computer's clock for the instant that the Sky Area Map
window is created. The Time option allows the user to display a
map for any other time and date. When this option is selected,
the "Observation Time" dialog is displayed.
Fill in the dialog fields for the time and date required.
Pressing the "Now" button will read the time and date from the
computer's clock.
Notes:
1. Although the map is drawn centred on a fixed point on the
RA/Dec coordinate grid, the date and time are still used to
calculate such things as planetary positions, and also, over long
periods of time, affect which stars are visible on the map, due
to the effects of proper motion and precession.
2. Dates before 1AD should be entered as negative numbers in the
normal astronomical manner. Enter the year 1BC as "0", 1000BC as
"-999", and so on.
3. Dates must be between 4000BC (-3999) and 8000AD, this being
the range over which the program's calculations are valid.
4. Dates on or after 0h on 15th October 1582 are assumed to be
in the Gregorian calendar; dates before then in the Julian
calendar.
5. The observation time is assumed to be a local time - ie, the
time as shown on an observer's clock. The time zone information
specified on the Observation Location dialog (see below) is used
to convert the time to UT.
Observer
The Observer option allows the user to enter information about
the location from which the observation is taking place. When
this option is selected, the "Observer" dialog is displayed.
27
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
The "Latitude" and "Longitude" fields specify the location of the
observer. Both are entered in degrees, minutes, and seconds
although, unless extreme accuracy is required, a position correct
to the nearest degree will normally suffice.
The "Conditions" information describes the atmospheric
temperature and pressure at the time of observation. This
information is used to calculate the effects of refraction, so
has no influence on the Sky Area map.
The "Local Time" data specifies the observer's time zone. It is
used to convert the time of observation (which is always assumed
to be local time) into UT or GMT. The time difference is entered
in minutes (not hours!) difference between local time and UT.
For example, an observer on the east coast of the USA, whose
clocks are set 5 hours earlier than GMT, should enter "300" (5 x
60) in this box, and click the arrow to change the text to
"before UT".
The "Daylight saving time" box should be checked if DST (called
"Summer Time" in the UK, and perhaps other countries too) is
currently in operation. If the box is checked, the local time is
assumed to be one additional hour ahead of UT.
Notes:
1. The reason that the time difference is entered in minutes,
rather than hours, is that not all countries are exact hours
ahead of or behind GMT. India, for example, is 5.5 hours (330
minutes) ahead of GMT.
2. The location of the observer is used by the Sky Area map when
calculating the effects of "diurnal parallax" for nearby objects
such as the Sun, Moon, and planets. This is the difference in
the apparent position of a nearby body against the star
background as seen from different places on Earth. In the case
of the Moon in particular, the correction for diurnal parallax is
important, and can alter the Moon's apparent place by up to 2o -
four times the Moon's apparent diameter!
Stars
The Stars option controls which stars are plotted on the map, and
also the way that plotted stars are displayed. When this option
is selected, the "Star Display" dialog is displayed.
The "Limiting magnitude of map" field determines the magnitude of
the faintest star whose position will be calculated. The higher
the number, the fainter the stars which will be displayed (and
the longer the map will take to compute). The star database
supplied with the program contains stars down to magnitude 7.0;
the full SAO star catalog has stars down to magnitude 9.5 or so.
28
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
The "Limiting magnitude displayed" field determines the magnitude
of the faintest star that will actually be displayed on the map.
Once a map has been drawn, you can change the value in this field
to temporarily suppress the display of the fainter stars on a
map, to remove "clutter". The value entered in this field should
be less than or equal to the value entered in the "Limiting
magnitude" field above..
The lower half of the dialog box controls the way that the size
of the star images varies with their magnitude. All stars
brighter than the first "Display mag" field will be displayed
using the size of star circle shown to its right. All stars
fainter than the second "Display mag" field will be displayed
using the size of star circle shown to its right. All stars with
magnitudes between these two limits will be drawn with an image
size inversely proportional to the magnitude (ie, the brighter
the star, the larger the image).
Notes:
1. The number of stars rises very quickly with magnitude.
Generally, increasing the limiting magnitude by one magnitude
will more than double the number of stars visible on the map, and
consequently the time taken to compute their positions.
Stars Labels
This option controls the way in which stars are labelled on the
map. When selected, the "Star Labels" dialog box is displayed.
The way in which stars are named has evolved over hundreds of
years. As a result, a lot of the brighter stars have many
different names. The "Label Preferences" box allows the user to
determine which, if any, of those names is displayed on the map.
"Proper Names" refers to the "popular" name of a star, such as
"Polaris" or "Rigel".
"Bayer Letters" refers to the convention of labelling the
brightest stars in each constellation with Greek letters, such as
"Alpha Centauri" or "Beta Cygni".
"Flamsteed Numbers" refers to the convention of labelling stars
in each constellation with numbers, such as "61 Cygni".
The "Label Options" box at the bottom of the dialog box
determines which stars are labelled. If "All stars" is selected,
then all stars which have the appropriate name will be labelled.
If "Brighter than magnitude" is selected, then only those stars
brighter than the number in the edit box will be labelled.
Notes:
29
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
1. This dialog only determines the way in which stars are
labelled. If order to actually display star labels, the "Star
Labels" option must be enabled on the "View" menu or the ToolBar.
2. If a star has multiple names, and more than one of the naming
options is selected in the "Preferences" box, the name highest up
the box will be displayed. Eg, if both the "Proper Names" and
"Bayer Letters" options are selected, the map would display the
name "Polaris" in preference to "Alpha Ursae Minoris" when
labelling the pole star.
Constellation Names
This option displays a standard font selector allowing the user
to select the font used to write constellation names on the map.
RNGC Objects
Selecting this option displays the "RNGC Options" dialog box,
allowing you to determine which deep sky objects are displayed on
the map.
The "Object Selection" box determines which catalogue will be
searched to find objects to display; the entire RNGC catalogue or
only Messier objects.
The "Object Types" box controls which objects will be displayed
on the map, based on their type. If the "All objects" box is
checked, then the other boxes in the group are ignored, and all
objects which match the other selection criteria will be
displayed. If the "All objects" box is not checked, individual
types of object can be selected using the other boxes in this
group.
The "Magnitude Limit" box allows you to control which objects are
displayed, based on a magnitude selection. If "All Objects" is
selected, then all objects matching the other selection
parameters will be displayed; if "Brighter than mag" is selected,
then only those objects brighter than the specified magnitude
will be displayed.
Finally, the "Label Objects" box, determines whether displayed
objects will be labelled. If the box is checked, objects will be
labelled. Messier objects will be labelled "M" followed by a
number (eg "M32"); other objects will simply have their RNGC
catalogue number displayed (eg "1985" refers to the planetary
nebula "RNGC 1985" ).
Notes:
1. This is a complex dialog box - the most complex in the
program! - but it gives you the ability to exercise very fine
30
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
control over the non-stellar objects which are displayed. For
example, you can make selections such as "only display globular
clusters in the Messier catalogue brighter than magnitude 11".
2. The program will only display those Messier objects that are
in the RNGC. Four objects in the Messier catalogue are not in
the RNGC, so will not be drawn. These are: M24 (a local
brightening of the Milky Way), M25 (the open cluster IC 4725),
M40 (the wide double star Winneke 4), and M45 (the Pleiades).
3. The RNGC is based on the NGC, compiled towards the end of the
19th century. As such, it contains many incorrect
classifications, based on the information available at the time.
For example, the Crab Nebula in Taurus, M1, we now know to be a
supernova remnant, but the RNGC classifies it as a planetary
nebula. The RNGC is, however, a catalogue of great historical
significance, and no attempt has been made by the author to
"correct" it.
4. The symbols used to draw non-stellar objects on the map have
been based on those used in the authoritative "Uranometria 2000"
star atlas.
Colours
This option displays a sub-menu allowing the user to select the
colours used for every item drawn on the map for either the
screen or the printer. When either "Screen" or "Printer" is
selected, the "Horizon Map Colours" dialog box is displayed.
To view or edit the colour of any map component, either double
click on the name in the listbox, or move the listbox highlight
to the name and press the "Edit..." button. Either way, a
standard colour selector box will be displayed, letting you
choose the colour for the item.
Notes:
1. Pressing the "Cancel" button will restore ___ all the colours to
their previous settings, not only the colour just edited.
2. The "Printer" colour settings only relate to the printing of
colour maps. Refer to the printing section of the manual for
further information.
Draw
Selecting this option will draw the map, using the current option
settings. You may press the <F5> function key as a "shortcut"
for this option.
31
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Using the Sky Area Map Using the Sky Area Map Using the Sky Area Map
Once the Sky Area map has been drawn, it can be manipulated in
various ways. Most of the options are the same as for the
Horizon Map, so they are just summarised here for ease of
reference.
Setting the Visibility of Objects
The top section of the "View" menu consists of a list of
"toggles" controlling the visibility of various items on the Area
map. Each item has a corresponding button on the ToolBar. If an
item has a tick mark alongside it on the menu, or its button is
in a "pressed" state on the ToolBar, it is currently visible on
the map. If it does not have a tick mark, or its button is not
pressed, it is not visible. The items are:
Stars
Star Labels
Planets
Constellation Figures
Constellation Boundaries
Constellation Names
Right ascension/Declination Grid
RNGC Objects
Changing the map scale
The "Zoom In" and "Zoom Out" items on the "View" menu may be used
to change the magnification of the map. The <F2> and <F3>
function keys are shortcuts for these operations, as are the
first two buttons on the ToolBar. These options operate exactly
as they do for the Horizon map.
Identifying Objects on the Map
To display information about any object visible on the map, move
the mouse pointer over the object, and press the right mouse
button. A pop-up menu will appear. Select the item you wish to
identify. A dialog box will appear displaying information about
the object.
Zooming to an Area Map
To display a new Area map centred on a particular point on the
current map, position the mouse pointer over the required point
and press the right mouse button. Select "Area Map..." from the
pop-up menu.
32
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Printing the Map
To print the map, choose the "Print" option from the "File" menu.
The options displayed are exactly the same as for the Horizon
Map.
33
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Displaying Pictures Displaying Pictures Displaying Pictures
One of the most exciting features of SkyMap is its ability to
display photographic images of astronomical objects. You can
build up your own collection of pictures which, together with the
maps, can really bring the sky to "life", and which are a superb
way to show astronomical objects to a novice on a cloudy night!
(Here in England we get a lot of cloudy nights!)
In order to display pictures, you really need a "SuperVGA"
display capable of displaying 256 or more colours at once. You
can display pictures on a standard 16-colour VGA display, but the
results will probably be pretty horrible!
Picture Formats Picture Formats Picture Formats
SkyMap can currently display picture files in the following
formats:
1. GIF files. GIF is probably the most popular of all image
formats currently in use. The format was specifically devised to
enable pictures to be easily transferred between different types
of computer, and there are literally tens of thousands on
pictures in GIF format available. SkyMap will display files in
either GIF87a or GIF89a format, and can handle both interlaced
and non-interlaced images. The only restriction is that only the
first image in a file can currently be displayed. GIF files for
the PC normally have an extension of ".GIF".
2. Windows "Bitmap" files. These are "device independent
bitmap" files created for use with Microsoft Windows. They
normally have an extension of ".BMP" (for uncompressed images) or
".RLE" (for compressed images). An increasing number of these
files can be found on bulletin board systems, normally made
available for use as Windows "wallpaper".
Displaying Pictures Manually Displaying Pictures Manually Displaying Pictures Manually
From the "File" menu, choose the "Open Image..." item. A
standard file selector will be displayed, letting you select a
file from any available drive or directory. Pressing the <OK>
button will create a new window in which the image will be
displayed.
Displaying Pictures Automatically Displaying Pictures Automatically Displaying Pictures Automatically
SkyMap has the ability to load and display pictures of certain
object automatically. This can be done for all RNGC objects, as
well as the planets, Moon, and Sun. In order to use this feature
of the program, carry out the following steps:
34
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
1. Find a nice picture of an RNGC object or planet in any
supported image format. You can use the "manual" method
described above to look through pictures until you find one you
would like to have as a "standard" picture for a particular
object.
2. Copy the picture to the directory containing the SkyMap
program, and rename the file to "OBJECT.EXT", where "OBJECT" is
the name of the object, and ".EXT" is the "standard" extension
for the image format - ".GIF" for GIF files and ".BMP" for bitmap
files.
For planets, the name used should be one of the following:
SUN
MOON
MERCURY
VENUS
MARS
JUPITER
SATURN
URANUS
NEPTUNE
For Messier objects, the name should be "M" followed by the
Messier number; "M32", for example.
For other RNGC objects, the name should be "NGC" followed by the
RNGC catalogue number; "NGC1530A", for example.
3. Now, if you draw a map and click the right mouse button over
an object for which a picture has been stored, you should find
that a "Picture of <object>" item appears on the resulting pop-up
menu. Selecting this item will display the picture in a new
window.
Notes:
1. When you click on a object, SkyMap will first of all look for
a file with a ".GIF" extension, and then for a file with a ".BMP"
extension. If files with both extensions are present, the GIF
file will be displayed.
Obtaining Picture Files Obtaining Picture Files Obtaining Picture Files
There are many sources from which picture files (particularly GIF
images) suitable for use with SkyMap can be obtained. Some of
these are:
1. Commercial information services such as CompuServe or BIX.
An especially good source is the CompuServe "Astronomy" forum
(type "GO ASTROFORUM" from any prompt), which currently has more
than 1000 astronomy and space-related GIF files available.
35
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
2. Bulletin board systems, of which there are a vast and ever-
changing number. Some of these specialise in astronomy and carry
a large number of GIF images.
3. Public domain and shareware software libraries.
4. If you have access to it, perhaps the best source of all are
the ____ vast resources of the Internet - a world-wide computer
network. Take a look, for example at the machine
"ames.arc.nasa.gov", in directory "pub/SPACE/GIFS".
5. Finally, if you get really stuck, I can supply you with GIF
images for the cost of the disks plus a small handling fee.
Refer to the separate registration form for details.
36
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Appendix A: Data Sources and Precision Appendix A: Data Sources and Precision Appendix A: Data Sources and Precision
The sources of the data used by SkyMap are as follows:
Stars Stars Stars
Smithsonian Astrophysical Observatory (SAO) star catalog, (SAO
Staff, 1966), 1990 machine readable version, as supplied on
NASA's National Space Science Data Center's "Selected
Astronomical Catalogs, Volume 1" CD-ROM.
The SAO star catalog is a catalog of 258,997 stars to epoch
J2000.0, and is reasonably complete down to magnitude 9.5 or so.
The star database supplied with the shareware version of SkyMap
contains all the stars from the SAO catalog down to magnitude 7.0
- a total of 15,931 stars. Larger databases, up to and including
the full SAO catalog, can be supplied to registered users of
SkyMap for a small fee - refer to the separate registration form
for details.
SkyMap rigorously reduces star positions from mean to apparent
place. The following corrections are applied:
Precession
Proper Motion
Nutation
Aberration
In the case of the Horizon Map, the apparent place is used to
compute the local altitude and azimuth of the star, and the
altitude is then corrected for the effects of refraction.
Planets and Sun Planets and Sun Planets and Sun
The positions of the Sun, and the planets Mercury to Neptune are
computed using a subset of Bretagnon and Francou's VSOP87
planetary theory, as described in the book "Astronomical
Algorithms", by Jean Meeus (Willman-Bell, 1991).
Spot checks against recent editions of the "Astronomical Almanac"
indicate that the mean error in the computed positions of the
planets is under half a second of arc, with peak errors of about
one arc second. For comparison, the apparent diameter of the
planet Neptune is about 2", whilst that of Jupiter is typically
35".
Moon Moon Moon
The position of the moon is computed from the ELP 2000-85 lunar
theory (Chapront-Touze and Chapront, 1988), which in turn is
37
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
fitted to the DE200/LE200 numerical integration of the Jet
Propulsion Laboratory (Standish, 1981).
Spot checks against the "Astronomical Almanac" again indicate
that the mean error in the computed position of the Moon is about
half an arc second, with peak errors around one arc second.
Non-Stellar Objects Non-Stellar Objects Non-Stellar Objects
For non-stellar objects, SkyMap uses the machine-readable version
of the "Revised New General Catalog of Non-stellar Astronomical
Objects" (Sulentic and Tifft, 1973), or RNGC. This is a modern,
revised and expanded version of the "New General Catalogue of
Nebulae and Clusters of Stars" (Dreyer 1888).
Time Corrections Time Corrections Time Corrections
Because of the irregularities in the Earth's rotation, the
theories of motion of astronomical bodies do not use Universal
Time (GMT), but a uniform timescale called Terrestrial Dynamical
Time (TDT). SkyMap uses TDT internally for all its calculation
of planetary positions, etc, but obviously the user specifies the
time for which a map is required in UT (or rather, in local time,
which is converted to UT).
The difference between TDT and UT is called "delta T", and
currently has a value of approximately 1 minute. It is currently
increasing at a rate of somewhat less than 1 second per year.
The problem is that the value of delta T can only be determined
historically (typically by analyzing the motion of the Moon), and
current and future values can only be estimated, whilst values
for the distant past (before the advent of modern astronomy) are
uncertain to the order of many minutes.
What this means in practice is that although the time of a total
solar eclipse in the year 1500BC could be computed to a precision
of a fraction of a second in TDT, the actual time in UT that the
eclipse occurs (hence the places on Earth from which it is
visible) will be uncertain to within several minutes.
The "Astronomical Almanac" lists the values of delta T for every
year from 1620 onwards (currently up to 1992), and provides
estimates of its value for the current time. SkyMap has all this
data stored, and interpolates or extrapolates in this table to
find values of delta T for dates between 1620 and 2000.
For dates beyond the year 2000, an estimate of delta T is made
using the method of L V Morrison and F R Stephenson, "Sun and
Planetary System" vol 96,73 eds. W Fricke, G Teleki, Reidel,
Dordrecht (1982).
38
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
For dates prior to 1620, an estimate is made using the method of
F R Stephenson and M A Houlden, "Atlas of Historical Eclipse
Maps", Cambridge University Press (1986). They estimate the
uncertainty to be 15 minutes at 1500BC.
39
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Appendix B: Dreyer Object Descriptions Appendix B: Dreyer Object Descriptions Appendix B: Dreyer Object Descriptions
The RNGC catalogue of non-stellar objects includes the visual
descriptions used by Johann Dreyer in his "New General
Catalogue", published in 1888. These descriptions are remarkable
for their information content, but can be somewhat daunting at
first. For example, the Dreyer description of the globular
cluster M3 in Canes Venatici is as follows:
GCL,EB,VL,VSMBM,*11
This can be translated as "Globular cluster, extremely bright,
very large, very suddenly much brighter towards the middle,
composed of 11th magnitude stars" - a pretty good description in
only 19 characters!
Similarly the galaxy NGC 2863 in Hydra is described as:
CF,S,E,BET2*12,16
which means "considerably faint, small, elongated, between two
stars of magnitude 12 and 16".
The description normally starts with a description of the
object's brightness and size. Dreyer adopted the scale used for
this from Sir John Herschel, and the order used may be confusing
to modern observers; for example, is "considerably faint"
brighter or fainter than merely "faint"? The other possible
source of confusion is that 19th century astronomers often called
a faint star "small" and a bright star "large", so one always has
to be careful to judge whether a description such as "pretty
small" refers to size or brightness!
The scale used is as follows:
Brightness Size
EF Excessively faint ES Excessively small
VF Very faint VS Very small
F Faint S Small
CF Considerably faint CS Considerably small
PF Pretty faint PS Pretty small
PB Pretty bright PL Pretty large
CB Considerably bright CL Considerably large
B Bright L Large
VB Very bright VL Very large
EB Extremely bright EL Excessively large
Next normally comes a description of object's general shape.
This lies on a scale ranging from "round" to "extremely
extended", as follows:
40
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Code Shape
R Round
VLE Very little extended
E Elliptic or oval
CE Considerably extended
PME Pretty much extended
ME Much extended
VME Very much extended
EE Extremely extended
By far the most cryptic part of the description, at first glance,
is the group of letters giving what Sir John Herschel described
as "the degree and rate of condensation". A simple example is
"GBM", meaning "gradually brighter towards the middle". Looking,
though, at NGC 4725, a galaxy in Coma Berenices, we find the
dreadful looking "VSVMBMEBN"! Even this mouthful, though, is
fairly easily translated as "very suddenly very much brighter in
the middle, with an extremely bright nucleus".
When the descriptions give directions on the sky, the terms
"preceding" and "following" are used for west and easy
respectively. To see what is meant by this, picture the way an
object drifts across the field of view of a telescope if the
drive is switched off. Use of these terms is much more natural
at the telescope eyepiece than the very confusing west and east,
given the way that optical systems invert and/or reflect the
field of view.
Quite often the notes speak of groups. The "1st of 4" is the
first member of a group of four nebulae to drift across the field
of view ie, the most western one, preceding all the others. All
members of a group will have very nearly the same declination.
The complete list of abbreviations used in the Dreyer description
of an object appears below:
Code Meaning
AB about
ALM almost
AM among
APP appended
ATT attached
B bright
B brighter (always coupled with another letter)
BET between
BF brighter toward following side
BIN binuclear
BN bright toward north side
BP brighter toward preceding side
BS brighter toward south side
41
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
C compressed
C considerably
CH chevelure
CL cluster
CO coarse, coarsely
COM cometic
CONT in contact
D double
D diameter
DEF defined
DIF diffused
DIFFIC difficult
DIST distance
E extended
E extremely, excessively
EE most extremely
ER easily resolvable
EXC excentric
F faint
F following
G gradually
GCL globular cluster of stars
GR group
I irregular
IF irregular figure
INV involved, involving
L large
L little (adv.), long (adj.)
M middle or in the middle
M much
MM mixed magnitudes
MN milky nebulosity
N nucleus or to a nucleus
N north
NEB nebula
NF north following
NP north preceding
NR near
P poor
P preceding
P pretty (before F, B, L, S) (size and brightness blocks)
PG pretty gradually
PLN planetary nebula
PM pretty much
PS pretty suddenly
42
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
QUAD quadrilateral
QUAR quartile
R round
R resolvable
RI rich
RR exactly round
RR partially resolved, some stars seen
RRR well, resolved, clearly consisting of stars
S small
S suddenly
S south
SC scattered
SEV several
SF south following
SH shaped
SM smaller
SP south preceding
ST stars
ST9 stars from the 9th magnitude downward
ST9...13 stars from 9th to 13th magnitude
STELL stellar
SUSP suspected
TRAP trapezium
TRI triangle, forms a triangle with
TRIN trinuclear
V very
VAR variable
VV very very, an intensive of V
* a star (or stars)
*10 a star of 10th magnitude
** double star
*** triple star
() items questioned by Dreyer enclosed in parentheses
" arc seconds (two "not-equals" in published catalogue)
' arc minutes (one "not-equals" in published catalogue)
43
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
Appendix C: SkyMap Release History Appendix C: SkyMap Release History Appendix C: SkyMap Release History
29-May-93 v1.3
New features:
The program can now display non-stellar objects. The database
used is the Revised New General Catalogue (RNGC).
Constellation boundaries can now be displayed.
The printing options have been greatly expanded. When a map is
printed the user can now select whether to print the entire map,
or the current zoomed view, and also whether to print in black
and white or colour. For colour maps a dialog allows the user to
select the colour of each component of the map.
All map features are now present on both the horizon and sky area
maps (eg star labels can now be displayed on the horizon map).
The user interface has been made more consistent between the map
types.
The program now has an optional ToolBar at the top of the screen,
which provides short-cuts for the commands on the "View" menu.
The program now (finally!) has a complete on-line help system.
This is basically a copy of the manual.
Bug fixes:
I'd forgotten to apply the correction for diurnal parallax to
planetary positions on the Sky Area map. Consequently, the
planets were being shown in their geocentric, rather than
topocentric positions, resulting in errors of up to 2 degrees in
the apparent position of the Moon. Fixed.
The size of the image of the Sun and Moon on the Sky Area map was
being incorrectly calculated, resulting in images that were about
50% too large when the map was printed on a portrait orientation
page. Fixed.
07-Mar-93 v1.2
New features:
Added a new "Sky Area" map type, centred on a right ascension and
declination. This is intended to be used to draw a detailed map
of a small region of the sky.
Added the ability to display photographic images in either GIF or
BMP format. Images can either be explicitly opened, or
44
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
associated with specific objects (currently planets) and
automatically displayed.
Bugs fixed:
Single pixel stars were being printed on the printer in the
screen colour, which almost certainly mapped to white on the
printer, resulting in them not being printed. On a mono print,
single pixel stars are now correctly printed black.
When the right mouse button was pressed over a horizon map to
display the pop-up menu, then the *right*, rather than the *left*
button pressed (ie, a user input error!) an incorrect cursor
position was stored. If the left button was subsequently used to
select an information dialog a wildly inaccurate position or a
GPF resulted. This is probably the cause of all the "random
number" errors previously reported. Thanks to Don Munro for
tracking down a reproducible case of this puzzling error! Fixed.
Removed the incorrect, uninitialized data displayed on the
information dialogs for the Sun and Moon. (Eg phase 0.000 for the
Sun.)
05-Feb-93 v1.11
Bugs fixed:
When the start of a constellation figure was off the edge of the
map, the first visible line of the constellation was being drawn
incorrectly in certain circumstances. Fixed.
The correction for refraction was being correctly calculated and
correctly displayed in the "About" box for a star, but not
applied to the plotted position of the stars on the map. This
led to stars being plotted with slightly too low an altitude (the
maximum error being about half a degree at the horizon). Fixed.
If the star position calculation was aborted by the user pressing
the "Cancel" button, the subsequent constellation figure setup
calculation code displayed an error message for each star it was
unable to find. Pressing the "Cancel" button now aborts the map
calculation cleanly.
31-Jan-93 v1.1
Release to BIX only for testing.
New features:
Version 1.0 of SkyMap simply plotted stars in their mean catalog
position. This version now rigorously calculates the apparent
45
SkyMap v1.3 Copyright (c) 1992-1993 C A Marriott
place for the time of observation, correcting for proper motion,
aberration, precession, nutation, and refraction.
Added code to verify that dates are in the range 4000BC-8000AD
(the range over which the planetary position equations are valid.
Bugs fixed:
In the "Observer" dialog, the "Time Difference" edit field was
only wide enough to allow two digits to be entered, making the
program not too useful for anyone outside the GMT time zone.
Fixed.
24-Jan-93 v1.0
Release of SkyMap 1.0, with basic facilities for drawing horizon
map and plotting planetary and lunar positions.
46