home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Atari Mega Archive 1
/
Atari Mega Archive - Volume 1.iso
/
apps
/
astronmy
/
stargide.lzh
/
STARPRG3.DOC
< prev
next >
Wrap
Text File
|
1985-11-20
|
22KB
|
448 lines
THE AMATEUR ASTRONOMER'S GUIDE TO THE NIGHT SKY.
Written by M.Kudlowski, December 1989, for the Atari ST 520.
1. Introduction.
2. Running the program.
3. The Constellation Chart option.
4. The Calendar Chart option.
1. INTRODUCTION.
This program is a guide to the stars and constellations visible in
the night sky from almost anywhere on earth. It features the following:-
1) 1160 stars down to magnitude 4.75, including variable stars
whose maxima exceed magnitude 4.75, and double or multiple
stars whose combined magnitude exceeds 4.75.
2) 370 selected stars which can be individually identified on the
Constellation Chart option. All stars of magnitude 3.5 and
brighter are included,together with all double and variable
stars on the main file.
3) 267 deep-sky objects which can be optionally plotted on the
Constellation Chart option. The limiting magnitude for these
objects is about 9 for clusters and gaseous nebulae, 10 for
external galaxies and 11 for planetary nebulae.
Most of these objects can be seen through a moderate telescope
of about 6 inches aperture, but the external galaxies and
planetary nebulae are mostly faint and elusive, and the gaseous
nebulae generally require a very transparent night for viewing.
2. RUNNING THE PROGRAM.
Note: This program can only be run in medium resolution.
To run the program, insert the disk in drive A and load
the program "STARPRG3.PRG". The data files take about 40
seconds to load, and while they are loading, a screen of
explanatory text is shown. When the files have loaded,
a menu screen appears with 3 boxed options:-
1) Constellation Chart Option.
2) Calendar Chart Option.
3) Quit program.
The Constellation Chart option draws a map of the constellation
as chosen by the mouse. There is also an option to include deep-
sky objects as well as including or excluding stars belonging to
adjacent constellations. The Own Choice allows you to define your
own region of sky to be displayed with an option of six scales.
The Calendar Chart option draws maps of the night sky as viewed
from any latitude,and at any date or time. Directional maps are
drawn for north,east,west,south and overhead aspects in addition
to a circular whole-sky plot.
The Quit option is the most drastic and should only be used
if you want to leave the program. For the other two options
you should click the left mouse button in the required box to
the left of your choice.
3.CONSTELLATION CHART OPTION.
3.1. THE CONSTELLATIONS.
There are 88 constellations in the sky and they vary in size from
sprawling groups like Hydra and Eridanus, which cover a quarter of
the entire sky, down to tiny constellations such as Crux and
Delphinus. To act as a guide to a constellation's size, each chart
includes a grid of celestial co-ordinates known as Right Ascension
and Declination.
The oldest constellations date back to Egyptian and Greek times, and
were catalogued by Ptolemy in his 'Almagest'. These are often termed
'original' constellations, and number 48.
Most of them are named after famous people and creatures in Greek
and other mythologies. Examples are Orion, Pegasus, Leo and Scorpius.
The far southern constellations, however, were unknown because they
could never rise above Greek or Egyptian horizons, and so it was
up to 17th- and 18th-century astronomers to add new groups in those
hitherto uncharted regions. A few minor groups were also added in
the northern heavens in faint regions unclaimed by the original
groups. It must be frankly said that some of these modern groups
were a waste of time - Leo Minor, Horologium and Caelum are notorious
examples. The constellation of Mensa is not even included here since
its brightest star is fainter than magnitude 4.75.
Also, Argo Navis,one of the 48 originals, was so large that it had to
divided up into three parts for convenience.
3.2. DRAWING THE CONSTELLATION CHART.
An explanatory screen will be displayed on entering the menu. On
pressing the left mouse button, an index screen of constellation names
will be displayed. To plot the chart, simply press the left mouse
button either in the box to the left of the constellation name or
on the name itself, and then press the left mouse over the text marked
'Ready', which will appear in the lower right of the screen.
The program then plots the stars making up the constellation, gives
the name of the constellation in Latin and English together with
its Latin genitive, and displays brief textual notes about the
constellation. The standard international abbreviated constellation
name is displayed in the upper right corner of the map.
Culmination dates and times are also shown on the left map margin
to inform when the constellation is at its best viewing position,
subject to its declination and the viewer's latitude. Thus, from
Northern Europe, at a latitude of 50 degrees north, all stars
south of declination -40 degrees are permanently out of sight.
Because the constellations are so variable in size, a coordinate
grid is included on the map for reference.
Pressing the left mouse button again will link up the constellation
figure to form a distinctive shape. From this point on, you can
identify individual stars by pressing the left mouse button above
them. If the star is one of those individually listed, then
details about the star will be printed on the screen. These include
its Greek or other letter, its (often-barbarous) Arabic proper name,
its visual magnitude, its spectral type, its distance in light-years,
its absolute magnitude and its celestial coordinates.
The coordinates of Right Ascension and Declination correspond to
latitude and longitude on the earth. The earth's axis is aligned
with the celestial poles, whose declinations are 90 degrees north
and south. The plane of the earth's equator, if extended, aligns
itself with the celestial equator, declination zero degrees.
The declination of a star is sufficient to determine if it is visible
from a given latitude. For example, the latitude of Manchester is
53 degrees north. Subtracting 53 from 90 gives 37, which means that
any star south of declination 37 degrees south can never rise.
In addition, any star north of declination 37 degrees north will never
set. All stars with intermediate declinations will spend a greater or
lesser period below the horizon.
Right Ascension is generally measured in units of time, and the zero
point of reference is the Vernal Equinox. On March 21, when the sun
is on the celestial equator, its right ascension is zero hours.
Culmination of a star occurs when it is at its highest position in
the sky. The Right Ascension of a star is the time it culminates after
the vernal equinox has done so. This gives an idea of the best times
for viewing a satr as follows.