Atari Forever 4/Atari Forever 4.zip/Atari Forever 4.iso/PD_THEMA/ASTRONOM/ASTROCAL/ASTROCAL.TXT

Text File | 1998-03-14 | 22KB | 576 lines

         Cadenza AstroCal (Version 2.0, October 31, 1988)


Program Features

This program generates (for any given year) a calendar  containing
the following information:

1.   Times of sunrise, sunset, moonrise, and moonset for each day
2.   Times and dates of Moon phases
3.   Times and dates of solar and lunar eclipses
4.   Times and dates of solstices and equinoxes

In addition to this calendar, the program can generate:

1.   A report of all lunar or solar eclipses for a range of years
2.   A report of planet viewing information for a specified year
3.   A  report  of  perihelions and aphelions  of  planets  for  a
     range of years
4.   A report of perigees and apogees of the Moon for a  specified
     year
5.   A report of the dates of Easter for a range of years
6.   A  diagram  of the positions of Jupiter's  bright  (Galilean)
     moons.
7.   A diagram of the positions of the brightest stars.

The  calendar  and  reports  are all  customized  for  the  user's
location.  All times and dates are in local time.

The calendar and reports can be printed on a printer or listed  on
the computer screen.


Hardware Requirements

This program should run on any Atari ST computer with a monochrome
or color monitor.   This program runs on color monitors in  medium
resolution only (please see the Bugs section below).   Of  course,
users  wanting  to  print out calendars and reports  will  need  a
printer.


Menus

AstroCal  has the following menus:  "Desk",  "Describe  Location",
"Generate Report", "File", "Display", and "Help".

The "Desk" menu can be used to run desk accessory programs, and to
see the "introduction box" of this program.




The "Describe Location" menu is used to specify one's location (in
latitude and longitude), and the difference between local time and
UT (universal time (sometimes called GMT (Greenwich Mean Time)).

The "Generate Report" menu has the following submenus: "Calendar",
"Lunar Eclipses",  "Solar Eclipses",  "Planet View Info",  "Planet
Distance",  "Moon Distance",  "Dates of Easter",  "Jupiter Moons",
and "Star Chart".

The  "File"  menu has only  one  submenu,  labeled  "Quit".   This
submenu is selected to quit the entire program.

The "Display" menu has two submenus,  "Scroll" and "Stop".  If you
select the "Stop" submenu,  the program will wait for you to  type
the  RETURN key after each page of text is listed on  the  display
screen.   If you would prefer that the program continuously  write
text on the display screen without stopping,  select the  "Scroll"
submenu.   The  "Display"  menu does not affect  the  printing  of
calendars and reports on a printer.

The  "Help"  menu  is  used to get  basic  information  about  the
program.


Getting Started

First  of  all  you will need to provide  the  program  with  some
information about your location and local time.   This information
is required to allow the program to customize its output for  your
location and time zone.

Select the "Describe Location" menu with the mouse.   Then  select
the "Describe Location" submenu.   At this point you should see  a
"dialog  box"  allowing  you to specify  your  city's  name,  your
latitude and longitude, and the difference between your local time
and UT.

Type  the name of your city in the space labeled "Location  Name".
Type  in  your latitude and longitude in the  appropriate  spaces.
Note  that  latitude  and longitude must  be  entered  as  decimal
degrees.   To convert an angle expressed in degrees,  minutes, and
seconds form to decimal degrees, use the following formula:

decimal degrees = degrees + minutes / 60 + seconds / 360

For  example,  if you know that your latitude is  32  degrees,  12
minutes,  and 44 seconds,  you will need to type in a latitude  of
32.21 since:

32 + 12 / 60 + 44 / 3600 = 32.21 (rounded)

If  you  live  north of the equator,  select  the  button  labeled
"North".  Otherwise select "South".

In  the same way,  enter your longitude in  decimal  degrees,  and
select the "West" button if you live west of  Greenwich,  England,
or "East" otherwise.

Finally,  enter  the  number of hours that you must add to  UT  to
convert to your local time.   If you must subtract from UT to  get
your  local  time,  enter  a negative number.   You  may  enter  a
fractional number (e.g. 4.5).

Users in the USA can use the following table:

Atlantic Time Zone                 Local Time = UT +  -4 hours
Eastern Time Zone                  Local Time = UT +  -5 hours
Central Time Zone                  Local Time = UT +  -6 hours
Mountain Time Zone                 Local Time = UT +  -7 hours
Pacific Time Zone                  Local Time = UT +  -8 hours
Most of Alaska                     Local Time = UT +  -9 hours
Hawaii Time Zone                   Local Time = UT + -10 hours


Once  this  information  is entered,  select  the  button  labeled
"Done".   This  information  will be saved in a disk  file  (named
astrocal.dat) and need not be entered again.

Note  that  AstroCal gives all times and dates in  local  standard
time, never in Daylight Savings Time or Summer Time.

Now  that  you've specified your location,  you  can  generate  an
astronomical calendar or a report.

Note about entering years:   if you want a calendar or report  for
the year 1988, enter 1988, not 88.  Negative years (i.e. B.C.) can
be entered.


Generating an Astronomical Calendar

Select  the  "Generate  Report"  menu,  and  then  the  "Calendar"
submenu.   At this point you should see a dialog box allowing  you
to  specify the year of the calendar,  the starting month  of  the
calendar,  and  whether  the calendar should be  printed  on  your
printer  or  on  the computer  screen.   Once  you've  given  this
information,  press  the "Done" button,  and the calendar will  be
generated.   If  you change your mind,  press the  button  labeled
"Cancel",  and the calendar will not be generated.   Preparing  an
astronomical calendar will take about one hour.

The   calendar  will  contain  several  abbreviations  which   are
explained in the Abbreviations section later in this document.





Equinoxes and Solstices in the Northern Hemisphere

The  celestial  equator  is the plane  described  by  the  Earth's
equator.   The ecliptic is the apparent path of the Sun across the
sky during one year.


Equinoxes  occur when the ecliptic crosses through  the  celestial
equator.   At  the  March  Equinox the Sun appears  to  cross  the
celestial  equator on its journey north.   The  September  Equinox
happens  when the Sun crosses the celestial equator  going  south.

Solstices  occur when the ecliptic is maximally north or south  of
the  celestial equator.   At the June Solstice the Sun is  as  far
north  of  the  celestial equator as  possible.  At  the  December
Solstice the Sun is as far south as possible.

Spring begins at the March Equinox,  Summer at the June  Solstice,
Fall  at  the  September  Equinox,  and  Winter  at  the  December
Solstice.

For the southern hemisphere,  switch north and south,  summer  and
winter, and fall and spring in the previous three paragraphs.


Generating an Eclipse Report

Select the "Generate Report" menu with the mouse,  and then select
the "Lunar Eclipses" or "Solar Eclipses" submenu.   At this  point
you  should see a dialog box prompting you for the range of  years
of  the report,  and whether the report should be printed on  your
printer  or  listed on your display  screen.   Press  "Done"  when
you've entered all of the information, or press "Cancel" to quit.


Interpreting a Lunar Eclipse Report

During a lunar eclipse,  all observers that can see the moon  will
see the same part (i.e.  moon enters shadow, maximum eclipse, moon
leaves shadow) of the eclipse at the same instant.   Thus for each
eclipse  in the eclipse report,  you will be able to view a  given
part of that eclipse if it occurs between the time of moonrise and
moonset on the day of the eclipse.


Interpreting a Solar Eclipse Report

This  program  does not compute the local circumstances  of  solar
eclipses.  Consequently, you will not be able to determine whether
a  solar  eclipse predicted by AstroCal will be  visible  in  your
area.



Generating a Planet Viewing Information Report

Select the "Generate Report" menu with the mouse,  then select the
"Planet  View Info" submenu.   At this point you will be  prompted
for the month and year at which the report will begin, and whether
you  want  the report printed on your printer or on  your  display
screen.   Press "Done" when you've entered all of the information,
or press "Cancel" to quit.


Interpreting a Planet Viewing Information Report

This report will help one determine whether or not a given  planet
will  be  visible  on a  given  day,  and  its  location.   Planet
locations  are  given  in right ascension  (expressed  in  decimal
hours)  and  declination (decimal  degrees).

The elongation of planets is given in decimal  degrees.   Consider
two rays originating at the center of the Earth, with one going to
the  center  of the Sun,  and the other going to the center  of  a
planet.  That planet's elongation is the angle between these rays.
If a planet's elongation is near 0 (or 360) degrees,  it will tend
not  to be visible from the Earth.

To  an earthbound observer planets,  like the Moon,  have  phases.
This report specifies the illuminated fraction of a planet's disk.
This is a number between 0 (for a planet that is not visible (like
the new Moon)) and 1 (for a planet whose disk is entirely  visible
(like the full Moon)).

This  report  also gives the distance between the  center  of  the
Earth  and  a  planet,   expressed  in  astronomical  units.   One
astronomical  unit  is equal to the average distance  between  the
Earth's and Sun's centers (149,598,770 km).


Generating a Planet Distance Report

A  planet  achieves perihelion when it comes closest to  the  Sun.
Aphelion occurs when a planet is at its greatest distance from the
Sun.   To generate a report specifying the dates of perihelion and
aphelion for planets,  select the "Generate Report" menu, and then
select  the "Planet Distance" submenu.   You will be prompted  for
the range of years of the report, and whether the report should be
printed  on your printer or listed on your display  screen.   When
you've entered this data,  press "Done" to generate the report, or
"Cancel" to quit.







Generating a Moon Distance Report

Perigee occurs when the Moon is closest to the Earth in its orbit,
and  apogee  when  it is most  distant.   At  perigee  the  Moon's
influence on tides is greatest.   To produce a report of the dates
of perigee and apogee,  select the "Generate Report" menu and  the
"Moon Distance" submenu.  Then enter the year of interest, and the
starting  month.   Decide if the report should be listed  on  your
display screen or printed on your printer,  or select the "CANCEL"
button to quit.   It will take about half an hour to complete this
report.

In the report,  the distances given are between the centers of the
Earth and Moon.   The diameter of the Moon is defined as  follows:
imagine  two lines:   one line extends from the Earth's center  to
the  rightmost part of the Moon's surface.   The other  line  goes
from  the center of the Earth to the leftmost part of  the  Moon's
surface.  The angle between these two lines is the diameter of the
Moon.   The  diameter of a body is also called the body's  angular
size or angular diameter.


Generating a Dates of Easter Report

Easter  is  defined  as  (usually)  the  first  Sunday  after  the
fourteenth  day  after  the first new Moon  after  March  21.   To
produce  a  report  of the dates of Easter for a  given  range  of
years, select the "Generate Report" menu and the "Dates of Easter"
submenu.   Then enter a range of years,  and decide if the  report
should  be  printed  on your printer or listed  on  your  computer
screen.  Finally, press "Done" to generate the report, or "Cancel"
to quit.


Generating a Jupiter Moons Report

Jupiter  has  17 or more moons.   Four of these (the  Galilean  or
bright moons) can be seen with binoculars.

This feature allows users to generate diagrams of Jupiter and  its
Galilean moons.

Select the "Generate Report" menu and the "Jupiter Moons" submenu.
Enter  the year,  month,  day,  and time (in local  time,  24-hour
format).  Then press "Done" to generate the report, or "Cancel" to
quit.   After generating the diagram,  hold down the shift key and
press the left mouse button,  and then you'll be able to run other
commands of the program.






Interpreting a Jupiter Moons Report

The  largest  circle  in  the center  of  the  diagram  represents
Jupiter, and the smaller numbered circles represent the moons:

1:  Io
2:  Europa
3:  Ganymede
4:  Callisto

The  diagram represents the view of Jupiter and its moons  on  the
specified instant, with the following caveats:

1.   The  diagram represents the view of Jupiter and its moons  as
     seen   through  an  inverting  telescope  in   the   northern
     hemisphere.   If you are viewing Jupiter through  binoculars,
     your view will appear to be reversed left-to-right.

2.   In  the  diagram,   Jupiter's  equator  is  even with  the  x
     axis   -  when  viewed  from  a  telescope   or   binoculars,
     Jupiter's  equator  (and  the  moons) will  tend  not  to  be
     even with the observer's horizon.

3.   The  diagram  does not specify if a moon is in  front  of  or
     behind the planet,  so if a moon appears in front of  Jupiter
     in the diagram, it may in reality be behind the planet.


Generating a Star Chart

To produce a diagram of the brightest stars in the sky for a given
night,  select the "Generate Report" menu with the mouse, and then
select the "Star Chart" submenu.   At this point you will need  to
specify  the  date  and  time (in local  standard  time)  for  the
diagram.   After giving the date and time, press the "done" button
to generate the diagram, or press "cancel" to quit.

The stars will be drawn in a diagram similar to those published in
popular  astronomy  magazines  every  month.    This  diagram   is
interpreted as follows:

The directions north,  south,  west, and east are labeled N, S, W,
and  E  on the diagram.   Note that west and  east  are  reversed.
Bright stars will appear larger in the diagram than dim stars.










Imagine that you are facing north,  looking at a printout of  this
star chart (with N facing north) placed at your feet.   If a  star
is  close  to  the N on the chart,  it can be  found  in  the  sky
straight  ahead and near the horizon.   A star near the center  of
the  diagram  will appear in the sky directly above you  (at  your
zenith).   The zenith of the star chart is marked with crosshairs.
A star which appears on the left of the chart (towards east)  will
appear in the sky to your left.  A star appearing near the chart's
right (west) can be found in the sky to your right.

When the star chart has been completely drawn on the  screen,  one
can  determine the name of a given star and its  constellation  by
placing  the center mouse (which looks like crosshairs)  right  on
top  of the star,  and pressing the left mouse button.   When  you
are  finished  with the star chart,  hold down the shift  key  and
press the left mouse button.

All  star  location  information is stored in a  disk  file  named
"stars.dat".  This file must be stored in the same subdirectory as
this  program.   Data on over 1,200 stars is stored in this  file.


Quitting Early

If  you  want  to quit in the middle of preparing  a  calendar  or
report,  press  the Undo key.   In a moment (but not  immediately)
you'll be given the opportunity to quit whatever you're doing  and
go on to something else (or quit the program entirely).


Quitting the Program

When you want to quit the entire program,  select the "File"  menu
and the "Quit" submenu with the mouse button.   If you've  changed
your location information,  you will be asked if you want to  save
the changes.   If you answer no,  your changes will be  discarded.
If you answer yes, the changes will be saved in a disk file (named
astrocal.dat)  and  will be available the next time  you  run  the
program.















Abbreviations

SR:   Sun Rise            SS:   Sun Set
MR:   Moon Rise           MS:   Moon Set
FM:   Full Moon           NM:   New Moon
FQ:   First Quarter       LQ:   Last Quarter
MEQ:  March Equinox       JSO:  June Solstice
SEQ:  September Equinox   DSO:  December Solstice
UT:   Universal Time      AU:   Astronomical Unit
RA:   Right Ascension     DEC:  Declination
DEGS: Decimal Degrees     HRS:  Decimal Hours
ELO:  Elongation          ILL:  Illuminated Fraction of Planet's Disk
DIST: Distance from Earth LMB:  Left Mouse Button


Note About Accuracy

The results of this program are not exact for three reasons:

1.   All computer floating point arithmetic is approximate.

2.   Simplifying  assumptions  in  the  astronomical  calculations
     result in a loss of accuracy.

3.   Some  of the astronomical calculations are optimized for  the
     present day,  and are not as accurate for dates far into  the
     past or future.

At  any rate,  values computed by AstroCal for years in  the  last
quarter of the twentieth century are usually accurate to within  a
few  minutes, with the following exceptions:

1.   Calculation of planet perihelion and aphelion:  dates for the
     Earth  may  be off by more than one day,  dates  for  Jupiter
     may be up to half a month in error,  and dates for Saturn may
     be off by more than one month.

2.   Calculation of Moon perigee and apogee:  the time of  perigee
     or apogee may miss the mark by an hour.


Bugs and Limitations

This  program  does not predict  penumbral  lunar  eclipses,  only
umbral lunar eclipses (most of the penumbra is not dark enough  to
have a noticeable effect on the Moon's brightness).

Umbral lunar eclipses having a very small magnitude may be missed.
For example,  AstroCal does not predict the lunar eclipse of March
3, 1988, which had a magnitude of only 0.003.




The star data file does not contain data about the proper  motions
of stars.   For this reason, the accuracy star charts of dates far
into the past and future is decreased.

Since this program was developed on a monochrome Atari  ST,  there
may be some problems running the program on a color system.

If  you  find  any bugs,  please report them to  the  author  (the
address is below).   This program is under continuous  refinement,
and  your  bug  reports and suggestions  will  contribute  to  its
improvement.


Further Reading

Mathematical astronomy is great fun,  and probably easier than you
think.   The  two  books that helped me the most  in  writing  the
program are:

1.   Astronomical  Formulae for Calculators by Jean  Meeus  (third
     edition), published by Willmann-Bell.

Meeus'  book  is  outstanding.   Although  the  methods  could  be
performed on a calculator,  they are certainly viable for use in a
computer program.   Most of the methods used in AstroCal are drawn
from this book.

2.   "Practical  Astronomy with your Calculator" (second  edition)
     by  Peter Duffett-Smith,  published by  Cambridge  University
     Press.

The  methods in Duffett-Smith's book tend to be less precise  than
the corresponding ones in Meeus' book.  However, this book is very
useful as a reference.   Some of the methods used in AstroCal  are
drawn from this book (chiefly coordinate transformations).

Duffett-Smith  has  also  written "Astronomy  with  your  Personal
Computer".  This book is for someone who simply wants to type in a
pre-written  program to do astronomical calculations.   There  are
many BASIC programs in this book,  but less background information
than in "Practical Astronomy with your Calculator".

The  following  book contains a wealth of information  about  many
different astronomical phenomena over a long span of years.  It is
extremely useful for verifying the accuracy of a program:

"Astronomical  Tables of the Sun,  Moon,  and  Planets",  by  Jean
Meeus, published by Willmann-Bell.

Donald  Menzel  and Jay M.  Pasachoff's "Stars and Planets"  is  a
colorful  and fun book.   It is very useful for those who want  to
find and observe various stars and planets.


Kim  Long's  "The Moon Book" (published by Johnson  Books)  is  an
interesting and fun book packed with  information,  diagrams,  and
folklore about the Moon.


Most almanacs contain much astronomical data.


Distribution of this Program

Since  Cadenza  AstroCal  is  public  domain,   users  may  freely
distribute  copies  of the program to other  users,  user  groups,
electronic bulletin boards, etc.


Payment

If  you like this program,  please send $5.00 US to the  following
address:

Eric Bergman-Terrell
Cadenza Software, Ltd.
1450 West 116th Avenue, #21
Westminster, CO  80234
U.S.A.

You  may  write  to  the same  address  to  report  bugs,  request
additional information,  suggest improvements in the program, etc.
If  you want a reply,  please include return postage (2  IRCs  for
those outside the U.S.A.).


Enjoy the program!