Category : Science and Education
Archive   : ASTRO202.ZIP
Filename : ASTRO.DOC

.

The graphical user-interface (GUI) should now replace the text-menu display on the screen. The
GUI is divided into two panels, on the left the button and information panel, and on the right,
the sky display (See page 4). At the top of the button-panel, below the title line, are three legends
used to indicate star magnitude (from -1 to +4), star color index (O to M), and 10 solar-system
objects (Sun, Mercury, Venus, Moon, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto). The Sun
and Moon are represented as squares and the planets as diamonds. For black and white displays,
(CGA, ATT6300, or EGA/VGA 2-color modes) the color-index legend will NOT appear.

Below the legends, an information panel gives the observer location and observation time. If a
mouse was detected, an additional information line appears for azimuth and altitude (the current
pointer position on the sky panel).

MOUSE: Move the mouse onto the sky panel and check that the cross in the centre of the
circle (the zenith point) labelled "Z", returns the altitude coordinate 90 and that
points on the circumference return 0. The azimuth values should increase from
0-360 anticlockwise from the top of the circle.

KEYS: Press to turn on the altitude-azimuth grid. The radial lines (azimuth) and
concentric circles (altitude) are 15 degrees apart and can be used to estimate
coordinates. Press again to toggle the grid off.

The GUI button-panel has 25 function buttons. The functions are explained in detail later in this
manual and in the on-line help files (accessed from the text-menu interface). For a new-user,
there are two important buttons to remember:

MOUSE: The exit button, {Big Q} icon and the animation toggle, {Big A} icon. Click on
{Big A} and the display on the right will step forwards or backwards in time (the
default step is one sidereal day.) During animation the mouse pointer is disabled
so to stop the animation you must hit or .

KEYS: or will Exit the GUI to the text-menu interface. is
a toggle to start and stop animation. will also halt time-step animation.

There is an important different between using and to halt an animation sequence.
preserves the display with the "trails" of the animated objects. Hit again and
the animation continues as if nothing had happened. erases all trails and redraws the sky
for the stop-time.

The sky panel, on the right hand side of the screen, is the main display area. In the default
startup configuration, you see a big circle (the horizon), a cross at the centre (the zenith point)
and a square (the Moon).

If you tried out animation, there may be some dots representing the track of the moon (and
possibly the sun). If the time and date is not 21:00:00 10/02/1989, reset it using the time-step
buttons in the lower left hand corner of the display. The highlighted ("turned on") arrowhead
indicates the current direction of time (Up forwards, Down backwards). The {Double Letter} or
{*} icons indicate the current solar ({HH} or {DD} or {MM} or {YY}) or sidereal ({*} or
{Three_*}) time-step.

MOUSE: Click on {Up_Arrow} to increment or {Down_Arrow} to decrement time by one
step. To cycle the solar step from hours to days to months to years and back to
hours click on {Double Letter}. Click on the {*} to change the sidereal interval
to the long {Three_*} step of 100,000 sidereal days (273 years). The icon changes
to 3 asterisks arranged in a triangle.

KEYS: increment, decrement the solar time-step.
increment decrement the sidereal time-step. ( S-for-short, one
day; L-for-Long, 100,000 days).

Note: the display is redrawn for every mouse-click or keystroke. On a slow machine, it may be
better to exit the GUI and reset the time and date in the pulldown [Data] menu.

Assuming, we are back in the GUI at 21:00:00 10/02/1989, we can add more to the display:

MOUSE: Click on {Planet} icon (the blob with the thick line through it) and, for the default
configuration, two planets (Mars and Jupiter) appear below and slightly to the left
of the Moon. The display should resemble the picture on page 4. Mars is nearest
the Moon. Click {Planet} again and the planets disappear.

KEYS: P-for-Planets toggles the display of planets. Wait for the screen to redraw
between keystrokes, on slow machines this may take a few seconds. Try not to
accumulate too many keystrokes as ASTRO will save and process them all
e_v_e_n_t_u_a_l_l_y!

ASTRO toggles, in addition too the {Planets} toggle, include:

Sun and Moon S-for-Sun
Star Magnitude M-for-Magnitude
Star Color C-for-Color index
Altitude-Azimuth Grid G-for-Grid
Ecliptic and Celestial Equators and Galactic Plane L-for-Lines

Deciphering the icons is left as an exercise (if intuition fails the Alt-keys still work, even if you
have a mouse).
If tried or you are now asking: WHY ARE THERE NO STARS? The
software features a cloudy night mode perhaps.....? The real reason is, that the default action of
ASTRO is not to read the star catalog stored in the support file "YALE.BIN". This file is not
needed for solar system objects and must be read explicitly from the [Data] menu. To read the
file, return to the text-menu interface or click on {Big Q} and select [Star_Catalog]
from the [Data] pulldown menu, the keystrokes are , D-for-Data, S-for-Star.

Now return to the GUI, from the [Plot] pulldown menu select [Plot_Star_Map] with the mouse
or ,

. Make sure that the date and time are the defaults 21:00:00 10/02/1989 and
toggle the star magnitude display . You should be able to see the Big Dipper to the left
and slightly above the zenith point. Check out the pointer to Polaris directly above the zenith.
The very large point a little above the southern horizon is Sirius. It has a special symbol with
a cross through the "circle" to make it easy to find. Look slightly above (to the North) of Sirius
and right (to the West) to find Orion. The three belt stars merge on the current display scale.

COLOR MONITOR: Flip to star color display . Sirius is green, Betelgeuse (top left in
Orion) is red, Rigel (bottom right in Orion) is cyan.

BW MONITOR: Take a break, or check out the [Star_Color] selection in the text-menu
interface. This allows selective display of stars by spectral class.

The lower right region of the button-panel is used to pan and zoom the sky map. To resolve the
belt stars in Orion, for example. Click on {Down_Arrow} or press the key to
pan down. The sky map appears to move up.

Now click on {+} or press the <+> key and the screen is redrawn at a larger scale. If you have
a slow cpu, and you are displaying 526 stars, the redraw may take about a minute. In such cases,
you may prefer to turn off the stars and planets , pan and zoom to where you
want to be, then toggle the stars and planets on again. Try panning and zooming around the sky.
ASTRO has a maximum zoom factor of x16 that increases or decreases by one for every mouse
click or keystroke.

To restore the original display, at any time, click on the big "H" or press or
H-for-Home. If you exit the GUI for any reason, when you return ASTRO remembers the toggle
and pan-zoom state and restores the display.

On final feature of note in ASTRO is the on-line help. Return to the text-menu interface {Big
Q} or or . Press to activate the [Info] menu. Now select [About] or
press A-for-About, to see who is responsible for ASTRO and this documentation. Any key
stroke or mouse-click will dismiss this blatant piece of self-aggrandizement. Next select [Help].
Guess which key? From the options in the [Help] menu, select [Menus], a help window will pop-
up on the left-hand side of the screen. Press any key or click on the arrow on the title bar to
close the help window. Now select [GUI Buttons], this is a more extensive piece of text so the
window has a scroll bar. Use the mouse on the arrowheads on the scroll bar or the arrow keys
to scroll. Outside the [Info] [Help] menu, hitting will bring up an appropriate help message
EXCEPT from the pulldown menu bar.

This has been a very brief basic introduction to ASTRO. For a comprehensive reference, see
section 2 for text-menus and section 3 for the GUI buttons. For some guidance on the
applications for ASTRO see section 4. Section 5 features a brief description of the development
history of ASTRO.

1.4 Saving Your Work
Hardcopy from ASTRO can be obtained by selecting the printer icon from the GUI or press
O-for-Output. This causes the program to write the complete screen to a file in one of
four in standard formats:

1. PRN file - IBM/Epson compatible screen dump.
2. PCL file - HPCL (Hewlett-Packard Print Control Language) screen dump.
3. EPS file - Encapsulated Postscript screen dump.
4. GIF file - GIF87a screen image.

ASTRO does NOT support direct printing. An intermediate file MUST be generated. Users are
recommended to use GIF files.

1.4.1 Printer Screen Dumps
PRN files are 37-45K depending on the screen mode. They can be copied to any Epson-
compatible printer.

PCL files are similar screen dumps for HPCL-compatible printers (such as the Laserjet).
File sizes are similar to those for the Epson printer.

EPS files are VERY LARGE. About 600K+ for a vga color screen. Take care that disk-
space is available when attempting to save the screen in this form. EPS files can be
copied to any Postscript printer.

It is NOT necessary to use the MS-DOS utility "GRAPHICS.COM" to print files
generated by ASTRO. When using the MS-DOS copy command, the /b (binary) switch
on the command-line MUST be used for .PRN and .PCL binaries or the screen dump may
be incomplete.

C:\ASTRO> copy astroXXX.prn lpt1: /b Epson compatible

C:\ASTRO> copy astroXXX.pcl lpt1: /b Hewlett-Packard compatible

C:\ASTRO> copy astroXXX.eps lpt1: Postscript compatible

If files are to be saved or transferred to other systems (eg Unix, VMS), then it is
recommended that Postscript files be compressed with ZOO, ZIP or ARC compressors.
This can reduce a 630K file (640x480 VGA screen) to about 13K. REMEMBER: PRN,
PCL, ZIP, ZOO and ARC files are binary formats (set the transfer type to binary). EPS
files are in ascii.

1.4.2 Graphics Interchange Format Files
GIF files are the recommended form of output from ASTRO. They provide a valuable
compact pictorial record in machine-readable form and can be readily printed. A typical
GIF is only 5-8K for the full-screen.

GIF file can be viewed or printed with a suitable utility. There are many excellent
freeware and shareware GIF utilities for viewing, manipulating and printing GIF files.
These include CSHOW, VPIC, VUIMG and GIFPRT.

C:\ASTRO> gif2scr astroXXX.gif

Try your local BBS or the DOS directories on the AU computer system to obtain a copy
of the latest version of such a package. Remember to register the one you choose to use -
you can try them out FREE!
ASTRO : TEXT-MENU SYSTEM


2.0 Introduction
The text-menu interface comprises a desktop with a title bar, pulldown menu bar and status line.
The pulldown selections are [Info], [Data], [Options], [Plot], and [Exit]. The menus are activated
either by mouse, arrow-keys, or Alt-keys (for example for [Exit]. The Alt-key for a
particular item is highlighted.

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³ Info Data Options Plot Exit ³
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The status line at the bottom of the screen indicates the video display adapter that has been
autodetected (even if a command-line switch was used to override).

2.1 Info
The [Info] pulldown menu (keystroke ) has three selections [Help], [Defaults], [About].
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³ Info Data Options Plot Exit ³
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³ Help ³
³ Defaults ³
³ About ³
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The [Help] selection pops up a list of help categories, [Defaults] allow inspection of current
parameter settings and [About] gives some information about the version and author of ASTRO.

2.1.1 Help
The [Help] selection (keystroke ) pops up a window of help categories:

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³ Help ³ Keystroke
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³ Data Entry ³
³ General ³
³ GUI Buttons ³
³ Hardware ³
³ Menus ³
³ Status Panels ³
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To select a category, enter the highlighted keystroke, click on the option with the mouse
or move to the option with the arrow keys and hit return. When a category is selected,
a help window will pop-up on the left-hand side of the screen. Press any key or click on
the arrow on the title bar to close the help window. The more extensive help windows
have a scroll bars. Use the mouse on the arrowheads on the scroll bar or the arrow keys
to scroll the text up and down. Outside the [Info] [Help] menu, hitting will bring
up an appropriate help message.

2.1.2 Defaults
The [Defaults] selection (keystroke ) pops up information panels for current
parameter settings but does NOT allow editing. The settings may be edited from the
[Data] and [Options] menus.

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³ Defaults ³ Keystroke
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³ Space-Time Co-ords ³
³ General ³
³ Animation ³
³ Star Magnitude ³
³ Star Color ³
³ Solar System ³
³ Output ³
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To select a category, enter the highlighted keystroke, click on the option with the mouse
or move to the option with the arrow keys and hit return. When a category is selected,
an information panel will pop-up on the right of the screen. Only one panel is displayed
at a time and the [Defaults] menu bar remains on the screen. A mouse click or the
key will dismiss the panel.

The [Space-Time_Co-ords] information panel gives the observers position in time and
space. Latitude, longitude, azimuth, date and time parameters are shown. The defaults are
the Latitude and Longitude of Athabasca, Alberta looking south (azimuth 180ø) in winter
on 10 February 1989 at 21:00 hrs (9:00pm).

The [General] information panel comprises a series of toggles for items to be shown on
sky plots. The symbol [þ] next to an option indicates that it is selected. By default the
options to show the Sun and Moon, the ecliptic and celestial equators, and the galactic
plane are enabled. The planets and stars options are disabled. See the [Options] menu for
further details.

The [Animation] information panel shows the animation time-step and the number of
steps per animation period. The defaults settings are for 100 steps of one sidereal day.

The [Star Magnitude] information panel shows the magnitude range(s) for which stars will
be displayed. The default is to make stars of every magnitude visible.

The [Star Color] information panel shows the spectral classes (O-M) or (blue to red) of
stars to be displayed. All spectral classes are selected by default.
The [Solar System] information panel shows a list of solar system objects that can be
displayed. By default, all objects, Sun, Moon and planets will be visible.

The [Output] information panel indicates the form in which the sky panel plot may be
saved. The default is [None] - nothing will be saved. The options consist of a set of file
formats for saving the graphics screen.

2.1.3 About
The [About] selection (keystroke ) pops up a window with information about the
version and authorship of Astro. The about window is dismissed by the key or a
mouse-click outside it's borders.

2.2 Data
The [Data] pulldown menu (keystroke ) has three selections [Position], [Date and Time],
[Star Catalog].

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³ Info Data Options Plot Exit ³
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³ Position ³
³ Date and Time ³
³ Star Catalog ³
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These menu selections provide for the entry of the observer position (latitude, longitude) and
viewing direction (azimuth); date (dd/mm/yyyy) and time (hh:mm:ss) of observation; and reading
the support file "YALE.BIN" containing the data for the 526 brightest stars.

2.2.1 Position
The [Position] menu selection (keystroke

) pops up a dialog box with the current
defaults for latitude, longitude and azimuth in (degs, mins, secs). Enter new values by
overtyping. The cursor will automatically skip non-numeric characters thus to enter the
latitude for Edmonton (53ø35'00") type only 0533500 or +5335. Notice that leading zeros
are required for all fields but that trailing zeros may be omitted.

Latitude values must be in the range +90 to -90, positive values are North of the equator.
Longitude values must be in the range 0 to 360 increasing from North in the sense NWSE
(counter clockwise) so that Edmonton is 113ø31'30". The same numerical longitude East
of Greenwich is 290ø31'30" (close to Canton, China). The NWSE direction convention
is used so that North American longitudes are in the range 0-180. Azimuth values (the
direction of view) must also be in the range 0 to 360 increasing from North in the sense
NESW (clockwise) so that NE is 45ø and NW is 315ø.

2.2.2 Date and Time
The [Date and Time] menu selection (keystroke ) pops up a dialog box with the
current defaults for date (dd/mm/yyyy) and time (hh:mm:ss). Enter new values by
overtyping. The cursor will automatically skip non-numeric characters thus to enter the
date 1 Jan 1992 type only 01011992. Notice that leading zeros are required for the day
and month fields. Times must be in the range 00:00:00 to 24:00:00.

2.2.3 Star Catalog
The [Star Catalog] menu selection (keystroke ) causes the program to attempt to read
the file "YALE.BIN" from the current DOS directory. A message box appears to indicate
reading is being attempted. If the read fails a dialog box pops up and requires an
acknowledging keystroke or mouse click. If the read succeeds a dialog box pops
up indicating the number of star data records read in. Again an acknowledgement is
required before the program continues. ASTRO does not need to read this file. The
motions of the Sun, Moon and planets can be studied without these data.

2.3 Options
The [Options] pulldown menu (keystroke ) has six selections [General], [Animation],
[Star Magnitude], [Star Color], [Solar System] and [Output]. [Options] provides editing access.

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³ Info Data Options Plot Exit ³
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³ General ³
³ Animation ³
³ Star Magnitude ³
³ Star Color ³
³ Solar System ³
³ Output ³
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The defaults for the GUI have been carefully selected and users with slow cpus are strongly
advised to use these (at least in the first instance).

2.3.1 General
The [General] selection (keystroke ) pops up a window of general options for the sky
panel.

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³ General ³ Keystroke
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³ þ Sun and Moon ³
³ Planets ³

³ Star Magnitude ³
³ Star Color ³
³ þ Ecliptic Equator ³
³ þ Celestial Equator ³
³ þ Galactic Plane ³
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The first 4 options can be reset from within the GUI. The final three options, to show
ecliptic and celestial equators and galactic plane, can only be enabled in this menu.
Options tagged by [þ] are enabled. To toggle the status of an option, enter the highlighted
keystroke, click on the option with the mouse or move to the option with the arrow keys
and hit return. The [Sun and Moon], [Planets], [Star_Magnitude] and [Star_Color] options
are enabling toggles that are duplicated as buttons in the GUI. [Star_Magnitude] and
[Star_Color] are mutually exclusive. Equators and planes can be switched on and off as
a group but NOT individually, by a button in the GUI. This menu enables a subset of
planes to be selected for display. The option window is dismissed by the key or
a mouse-click outside it's borders.

2.3.2 Animation
The animation option allows the user to select the number of time-steps to advance for
an animation period. The default is 100. A higher number may be appropriate for a fast
cpu. The time-step can be set from the GUI but the number of steps cannot.

2.3.3 Star Magnitude
The [Star Magnitude] selection (keystroke ) pops up a window of magnitude range
options:

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³Magnitude Options³ Keystroke
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³ All ³
³ þ < -1.0 ³ <<>
³ þ -1.0 to 0.0 ³ <0>
³ þ 0.0 to 1.0 ³ <1>
³ þ 1.0 to 2.0 ³ <2>
³ þ 2.0 to 3.0 ³ <3>
³ þ 3.0 to 4.0 ³ <4>
³ þ > 4.0 ³ <>>
³ None ³
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Options tagged by [þ] are enabled. To toggle the status of an option, enter the highlighted
keystroke, click on the option with the mouse or move to the option with the arrow keys
and hit return. All options are enabled by default. This menu enables a subset of stars to
be selected for display by magnitude. The option window is dismissed by the key
or a mouse-click outside it's borders. The [All] and [None] selections toggle every
magnitude range on and off.

Note: the use of for "All" and for "None" is for consistency with other menus
where and are used for other selections.

2.3.4 Star Color
The [Star Color] selection (keystroke ) pops up a window of spectral class options:
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³ Color Options ³ Keystroke
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³ All ³
³ þ O blue ³
³ þ A blue-green ³
³ þ B green ³
³ þ F white ³
³ þ G white-yellow ³
³ þ K orange-red ³
³ þ M red ³
³ None ³
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Options tagged by [þ] are enabled. To toggle the status of an option, enter the highlighted
keystroke, click on the option with the mouse or move to the option with the arrow keys
and hit return. All options are enabled by default. This menu enables a subset of stars to
be selected for display by color (really spectral class). The option window is dismissed
by the key or a mouse-click outside it's borders. The [All] and [None] selections
toggle every spectral class on and off.

2.3.5 Solar System
The [Solar System] selection (keystroke ) pops up a window of options for the
display of the Sun and Moon, and planets:

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³ SS Options ³ Keystroke
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³ All ³
³ þ Sun ³
³ þ Moon ³
³ þ Mercury ³
³ þ Venus ³
³ þ Mars ³
³ þ Jupiter ³
³ þ Saturn ³
³ þ Uranus ³
³ þ Neptune ³
³ þ Pluto ³

³ None ³
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Options tagged by [þ] are enabled. To toggle the status of an option, enter the highlighted
keystroke, click on the option with the mouse or move to the option with the arrow keys
and hit return. The [Sun and Moon] selection in [General] enables the group Sun and
Moon, the [Planets] selection enables the remainder. This set of options allows a subset
of planets to be selected for display or the Sun or Moon to be isolated. The groups
selected here may be toggled on and off in the GUI. The option window is dismissed by
the key or a mouse-click outside it's borders. The [All] and [None] selections
toggle every solar system object on and off.


2.3.6 Output
The [Output] selection (keystroke ) pops up a window of screen output options:

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³ Output ³ Keystroke
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³ þ None ³
³ PRN File ³

³ PCL File ³
³ EPS File ³
³ GIF File ³
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Options tagged by [þ] are enabled. To toggle the status of an option, enter the highlighted
keystroke, click on the option with the mouse or move to the option with the arrow keys
and hit return. PRN, PCL and EPS files are the equivalent of a screen dumps to
IBM/Epson, Hewlett Packard and Postscript compatible graphics printers. The GIF file
is in GIF87a format. The option window is dismissed by the key or a mouse-click
outside it's borders. Multiple files may be written if the appropriate options are enabled.
Note: in such cases ASTRO may have to scan the screen image more than once and the
operation may take a significant amount of time. A line is drawn on the right hand side
or at the bottom of the screen to indicate the progress of a screen dump. The line is
erased when the dump is complete.

2.4 Plot
The [Plot] pulldown menu has only two options: [Plot Star Map] and [Cancel].

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³ Info Data Options Plot Exit ³
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³ Plot Star Map ³
³ Cancel ³
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The [Cancel] option enables the user to avoid the time-penalty of accidentally entering the GUI.

2.4.1 Plot Star Map
The [Plot Star Map] selection (keystroke

) transfers from the text-menu interface to
the graphical interface of ASTRO. Before entering the GUI, the key will pop up
a useful help window.


2.4.2 Cancel
The [Cancel] selection (keystroke ) simply causes ASTRO to exit from the [Plot]
pulldown menu.

2.5 Exit

The [Exit] pulldown menu has only two options: [Exit] and [Cancel].

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³ Info Data Options Plot Exit ³
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³ Exit to DOS ³
³ Cancel ³
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The [Cancel] option is a safety feature to avoid loss of work by inadvertent exit.

2.5.1 Exit to DOS
The [Exit] selection (keystroke ) returns to DOS.

2.5.2 Cancel
The [Cancel] selection (keystroke ) simply causes ASTRO to exit from the [Exit]
pulldown menu.
ASTRO : GRAPHICAL USER INTERFACE BUTTONS


3.0 Introduction
The graphical user interface (GUI), is accessed by selecting [Plot Star Map] from the [Plot]
pulldown menu. It comprises a set of 25 icon-buttons that control the sky display panel. Many
of the buttons can be preset in the text-menu interface affording flexibility. This feature is
particularly valuable to users with a slow cpus since GUI redraw-overhead can be avoided by exit
to the text-menu for option changes.

3.1 Toggles
Toggles are switches that cycle the on/off condition. The GUI has a number of such switches.
On color displays, when a switch is toggled the icon on the button changes from dark gray (on)
to white (off). On black and white displays, the icon switches from black on white (on) to white
on black (off). On some 2-color laptop displays this may be reversed. Check the defaults to find
the sense of the display for such cases. The {Sun and Moon} toggle is on in the default startup
data.

3.1.1 Sun and Moon
The {Sun and Moon} icon (keystroke ) is two overlapping circles in different
colors. The button toggles the display of the Sun and Moon on the sky panel. Objects
(Sun or Moon) that have been "turned off" in the [Solar System] options menu are not
displayed.

3.1.2 Planets
The {Planets} icon (keystroke ) is a circle with a diagonal line through the
centre. The button toggles the display of the planets on the sky panel. Only those planets
that have been "turned on" in the [Solar System] options menu are displayed. Note: the
contrast for red against the default star panel background (blue) is poor. The "trail" of the
planet Mercury may be difficult to discern for some users. In such cases, try adjusting the
contrast and brightness controls on your monitors. On 2-color displays, all trails are
white-on-black. Users are advised to isolate one or two objects in the
[Options][Solar_System] menu before plotting trails.

3.1.3 Star Magnitude
The {Star Magnitude} icon (keystroke ) is two stars of different sizes in the
same color. The button toggles the display of star magnitudes on the sky panel.
Magnitudes are in the range -1.0 to +4.0 are display as filled circles with a radius
proportional to brightness. That is, the brightest star, Sirius, is biggest. Only those ranges
enabled in the [Star Magnitude] options menu are displayed.

3.1.4 Star Color
The {Star Color} icon (keystroke ) is two stars of different sizes in different
colors. The button toggles the display of star colors on the sky panel. Stars are displayed
by both magnitude and color index (OBAFGKM).

The correspondence between spectral type and screen color in 16-color graphics modes
is:

Spectral Class Screen Color

O very blue Light Blue
B blue Light Cyan
A green Light Green
F white White
G white-yellow Yellow
K orange-red Light Red
M red Red

Only those spectral classes enabled in the [Star Color] options menu are displayed.

3.1.5 Animation
The animate {Big A} icon (keystroke toggles continuous time-stepping with
current time-step. All display objects (Sun, Moon, planets, stars) are redrawn as single
pixels to mark track through the sky panel. If the step is an integral number of sidereal
days the stars remain static so ASTRO does not have to update their positions for short-
term simulations. There is little or no overhead involved in having the stars displayed as
a backdrop to solar system animations if a sidereal day is used as the time-step.

3.1.6 Grids
The {Grids} icon (keystroke ) is an open circle with two mutually perpendicular
diameters drawn. The button toggles the display of the altitude-azimuth grid (concentric
circles and radial lines drawn every 15 degrees) on the sky panel. Note: the time to
redraw the grid may be several seconds on slow cpus.

3.1.7 Lines and Planes
The {Lines} icon (keystroke ) is an open circle with an arc passing through the
horizontal diameter. The button toggles the display of the lines representing the ecliptic
and celestial equators and the galactic plane on the sky panel. Only those planes that have
been "turned on" in the [General] options menu are displayed.

3.1.8 Text
The {Big T} icon (keystroke ) toggles the display of text (azimuth directions and
object labels) in the GUI. The {Text} button will eliminate all text from the sky panel.
Note: selective text elimination is not possible in this version of ASTRO.

3.1.9 Daylight Savings
The {Daylight_Savings} icon (keystroke ) is a circle with multiple short rays
extending from the circumference. The button toggles between local standard time (LST)
and local daylight savings time (LDT) for data entered through the [Date and Time]
selection in the [Data] menu. The default is LST.

3.2 Time-Stepping and Animation
ASTRO offers a great deal of flexibility in single-stepping and multiple-stepping (animation)
through time. The program remembers the sense (forwards or backwards) and size of the current
time-step (solar hour, day, month, year or sidereal day or 100,000 days) and uses it for animation.
The time-step on startup is one sidereal day. The time-step icons are located in the lower left
hand corner of the GUI and comprise 6 buttons. The arrow head icon of the current time step is
highlighted in the GUI. The icon between the two pairs of up and down arrows indicates the size
of the solar and sidereal time-step: {HH} for hours (the solar time-step default), {DD} for days,
{MM} for months, {YY} for years, {*} for sidereal days (the sidereal time-step default) and
{Three_*} for 100,000 sidereal days.

3.2.1 Solar Time Step or