DISTANT SUNS 4.1 Demo Version Copyright 1992 by Mike Smithwick Welcome to the DISTANT SUNS demo! This is a near complete working copy of the Amiga planetarium program, DISTANT SUNS available from Virtual Reality Laboratories. This program may be freely redistributed as long as this file is kept intact. Originally named "Galileo" when it first appeared on the market in 1987, DISTANT SUNS has earned a reputation as one of the most complete general purpose computer planetarium programs. Now in its fourth version, DISTANT SUNS has collect numerous awards. It was named "Most Innovative Educational Product of 1988" at the Summer 1988 Consumer Electronics Show. In 1989 the readers of Amazing Computing selected it as their favorite educational software, and in the same category, the Amiga developer's community give DISTANT SUNS the "Developer's Choice" award at the 1991 Commodore Developer's Conference. DISTANT SUNS requires a machine with 1 meg of memory or more. While it will run on a stock 68000 Amiga it is easy to load the program down so much as to make the operation quite slow. Many tools are supplied to turn off objects and features when not needed to speed up operation. Two demo versions of DISTANT SUNS are available. The "1.3/FFP" version runs under 1.3 and uses software floating point calculations. The "2.0/FPU" version needs AmigaDos 2.0 and a floating point coprocessor, such as the 68881 or 68882 chip (which will speed things up at least 3 times). DISTANT SUNS is normally distributed on 3 disks, in order to trim it down to fit on a single disk a number of compromises had to be made. The normal distribution star database contains about 4200 stars which had to be cut down to just over 3700 (all stars brighter than magnitude 5.7), or about 2/3rds of what the human eye can normally see (about 6000). The lunar images have also been limited. In the real software different bitmapped images are supplied for each day. These took up too much disk-space, so only 6 lunar phases are supplied. This demo will limit you to observing in the year 1986 only. 1986 was selected so you could observe Halley's Comet in case you missed it. AREXX has been disabled, as well as overscan support, although high- res and medium resolutions are available. You cannot precess the stars nor can you add new orbits to the system (comets, asteroids, etc.). The anim facility has been disabled, however anims made by DISTANT SUNS may be available on your local BBS. You cannot save a screen to IFF or save events to a file. The "Twilight" and "Startrail" options have also been turned off. You will be unable to use any of the "Extended Star" databases, which would normally give you access to up to 255,000 additional stars. I know that this is probably overkill for a demo version, but some of the options just took up too much space, so getting rid of them was more out of necessity to free up room on the disk then to limit usability. Getting Started The demo distribution disk is not bootable. Meaning that if you are running only a floppy based system you will have to use your normal Workbench disk in the normal fashion. Before starting up the program, click on the "Install Fonts" icon. This will install 3 fonts that DISTANT SUNS needs into your font directory. Make sure to have about 5K of memory free if you're running from a floppy based system. If you have a harddrive, simply drag the "ds" icon over to the desired directory on the hard-drive. The program must be started up from the parent directory, otherwise it will not be able to find the need files. Once installed, you may click on either of the icons to start the program. "Ds_4.1" will start up the program in it's default configuration, and "halley's comet" will start it up looking back at the solar-system at the nearest approach of the comet. The default startup configuration will center the north star, Polaris, in the middle of the screen. The field-of-view (FOV) is at 180 degrees, so you see the entire northern hemisphere of the sky. Your mouse serves as the main navigation tool. In the default "point and center" mode, merely click anywhere on the screen with the left mouse button, and this point will snap to the center. You will also notice the simple control panel. The two buttons control the field-of-view. You are limited to values between 180 degrees (like a wide angle camera lens) and 1 degree. An angle of about 60 degrees is most natural. (Besides those buttons you can also zoom in via the FOV menu, under "Display" or by the drag-zoom mouse option found in the "Preferences" menu, discussed later). DISTANT SUNS defaults to a non-interlaced screen, 640x200. If you have more than 1 meg you may want to run in interlaced mode doubling the resolution and creating a much more pleasing display. In order to do so you will have to change the tool-types as described at the end of this document in the section called "startup configuration". BASIC CONCEPTS It is at this point that we ought to take a brief moment to explore some of the basic concepts of observational astronomy, which will help you in working with DISTANT SUNS. For starters, it is helpful to think of the sky in the same way the early astronomers did -- by imagining the stars and planets as being attached to the inside of a hollow sphere with the earth at the center. This sphere, in turn, revolves around the earth, creating the stellar motions. Variations on this theme had each planet on a separate crystalline sphere revolving on its own, which explained their independent movements. But for now, the single sphere model will do. Another concept which is essential for understanding how astronomers describe the various locations of celestial objects is that of coordinate systems. We are all familiar, in one way or another, with coordinate systems. This is a method of specifying the location of a particular place, be it on a piece of paper or the Earth. Our home addresses for example, represent one coordinate system, the earth's latitude and longitude lines are another. In order to pinpoint the location of a star, astronomers have developed their own system for the sky analogous to the earth's. The sky's latitude is termed "declination", (or "dec") and its longitude "right ascension", (or "RA"). In this "equatorial coordinate system", declination is measured in degrees, as is latitude, and like latitude, ranges from -90 degrees to +90 degrees. Zero degrees declination is called the "celestial equator". Right ascension, on the other hand, is measured not in degrees, but in hours, minutes and seconds, with each hour being the equivalent of 15 degrees. A second coordinate system that is important is the "horizon" system used in specifying the location of an object in your own sky. The two coordinates used are "azimuth", or compass heading with North being 0 degrees, and "altitude", or the angular elevation above the horizon. Both are measured in degrees. And while right ascension increases by motion towards the left, azimuth increases to the right. Because of the earth's rotation, horizon coordinates of a particular object are constantly changing, while its equatorial coordinates are constant. DISTANT SUNS defaults to using the equatorial coordinate system called "Planetarium Mode", as opposed to your local coordinate system. This was done for two reasons : * Planetarium mode is much faster which makes navigating around the sky all the easier. * Planetarium mode removes the ambiguities introduced by using your local system. That is, Rigel's equatorial coordinates are going to always be the same, but its local horizon position changes constantly. MENU CHOICES Now that you've had a chance to checkout the control panel, let's look at the menu choices available to you. The following sections will summarize the options. (Notice that a number of the menu items have keyboard equivalents, and that some options are mutually exclusive with others. Selecting these will automatically lock out others). ------------------- SYSTEMS MENU ------------------- The Systems Menu supports basic systems level and initialization functions. About DISTANT SUNS This will display authorship and copyright information. It keeps the lawyers happy. As this is a demo version it may be freely redistributed as long as this file is kept intact and with the software. AREXX (not available in this version) Selecting "open" will permit DISTANT SUNS to accept AREXX commands. AREXX is a high-level language which was designed to control programs externally. For instance, you may use AREXX to have DISTANT SUNS control a telescope. Or you may create a new interface using a combination of AmigaVision and a touch-screen for a museum exhibit. If you are running AmigaDos 2.0, AREXX is included. Otherwise you may buy it from your local dealer. Clock (new to version 4.1) The "control" option opens up a panel which will permit you to control how the programs internal clock behaves. When first opened, the system will read some interpolation tables off of the disk to initialize internal arrays. There are 5 different clock modes selectable in the "mode" cycle gadget, the default being "fast". With the fast mode chosen, clicking on the left or right arrows with the left mouse button will increment or decrement the date and time, based on the selected increments and units. Holding down the mouse button will cause the time to continue to change as fast as the machine will allow, until the button is released. (A math coprocessor is highly recommended for this feature, increasing the speed by about 300%). When in this mode, the moon's phase will not update until you release the button, nor will the solar corona load in during an eclipse. This was done for the sake of speed. Also, any object locks are temporarily disabled. In order to demonstrate this, center the sun using the "search/sun" selection in the Display menu. Set the increments to 1 day (should be the default), mode to "fast", and click on the left arrow. You will notice the sun, moon and planets all moving ahead in time. The moon will move the largest amounts, covering about 15 degrees per day. The "real" mode, sets the system to real time. The screen will update about once every half minute, keeping track with the system clock. This is useful if your are out in the field, so the display will match the sky all of the time. "Freeze" stops the clock activity altogether. "Manual" will quickly update the clock once with each click on the arrows. This will give you very fine control over the system to investigate more closely timed related events. Manual is no different then changing the time in the Environment window and hitting USE, and is included here for convenience. Because of this, the "trail" options in the Prefs menu have no effect. "Auto" is just like manual except it will automatically update the screen continuously, leaving a few seconds between updates so you can have access to the menus. And like "manual" it too will not leave trails. Also in the Clock menu is the "real-time" and "freeze" options. These are identical to the modes in the control window, acting as alternatives to those selections if the window is closed. So if "auto" is on and you wish to turn it off, instead of having to open the window and cycle through the modes, merely select "freeze". Environment At startup, DISTANT SUNS will read the current date and time from your computer's internal clock. If you haven't set it, you'll need to put in these values yourself. Selecting "environment" will open up a large window showing the current time, location, etc. needed by DISTANT SUNS at startup. You may change any of the values at will by simply clicking on them with either of the mouse buttons. The left button will increase the displayed value, the right will decrease it. A single click of the buttons will change the value by one step, whereas holding down on the button will cause the values to cycle automatically. The longer the button is held, the faster they will change. In order to make use of the right mouse-button the menus are not available from this window. In order to access the menus, merely activate any one of the other window and use the right button in the normal fashion. DISTANT SUNS tries to account for the proper time-zone depending on the supplied longitude. Unfortunately, due to the irregular nature of the zonal boundaries it is impossible to be sure if the calculated figure is correct. Moreover, not all countries, states or regions adjust for daylight vs. standard times. DISTANT SUNS always assumes standard time. If the longitude is changed to another time-zone, the value will be recalculated for standard time. DISTANT SUNS will allow you to enter any date between 4713 BC and 9999 AD. However, the further you go from the current date, the less accurate the calculations are likely to be. This is due to the many subtle motions in both the earth and stars. Also with this wide of time span we may come across precision limitations with the systems math libraries. If you made a mistake when changing the parameters, clicking on "cancel" will return to the values present when the window was opened. "EXIT" will merely close the window, while "ok" and cause the program to make use of the new data but will not exit. (These button conventions are consistent throughout the entire program.) Clicking on "save" will save the location data, which will be used for the default startup in the next session. The "julian date" is the "absolute" date used to pinpoint astronomical events. This is the number of days from the date (the "fundamental epoch") January 1, 4713. "UTC" is the "Coordinated Universal Time", better known as Greenwich Mean Time, or the time at the Greenwich Meridian. This is used as an absolute time whenever one needs to coordinate activities which stretch across time-zones. The default location is set for San Francisco. Flushmem If you are running with limited memory, you may run too low to perform certain operations if too many objects are loaded. Flushmem will purge the internal memory of some of these extra objects. Currently this will take care only of the "Extended Stars". Mem monitor This will display a simple memory monitor which you may want to check periodically when running on a 1 meg machine with alot of data loaded. Quickview Quickview will quickly set up the display in Local mode, oriented toward any one of nine directions, much like a macro. The horizon line, and constellation and planetary names will also be switched on. This saves you the time it would otherwise take to turn on everything separately and wait through several screen refreshes. The horizon line indicates where your own horizon is, marking every 10 degrees. The "up" option will display the entire sky as seen from the selected location. (Because of the wide field-of-view, the constellations near the edges will be "scrunched up",looking like the sky is viewed through a fish-eye lens.) The display is drawn as if you were outdoors, oriented North, looking up. That way, North would be "below" your chin, or down relative to your face. No Exit is required from Quickview--just select your options as you normally would. Redraw With the many options that DISTANT SUNS offers it is possible that from time to time various screen elements may trash others. Redraw will simply refresh the entire screen to clean it up if possible. Reset display Sometimes you may want to turn off all of the objects and identifiers previously loaded onto the screen. Reset will turn off all selected items all at once, returning the sky to a plain unadorned state. Reset clock to present (new to version 4.1) This is a painless way to reset the time and date to current values. State A "state" is the current configuration of the program, time, location, options selected, lookangle, and so on. This option will permit you to save and restore various states to your liking. One sample state is available demonstrating Halley's Comet. In this demo version you may not save a state. Quit Exits the program (so what else is new?). -------------------- DISPLAY MENU -------------------- The Display Menu will controls the major display elements and operation modes. Mode There are two main display modes DISTANT SUNS uses : "Local" and "Planetarium". In Local mode, the sky will be displayed as seen from the supplied time and location. Using Quickview under the System menu is the suggested way of entering Local mode to save time spent in setting up the screen to the most common configuration. Under this mode, the sky changes from night to night and from one point on Earth to another. Furthermore, the local coordinates of the stars, their "altitude" and "azimuth", will change as the Earth rotates. If you are in the Northern hemisphere you will notice the North Star, Polaris is at an altitude above the Northern horizon equal to your latitude. Were you exactly at the pole, the sky would resemble Planetarium mode. The default location is set for San Francisco. In Planetarium (the default) mode, the sky is displayed as if there were no earth underneath to distort your perspective. This removes any ambiguities that your own location introduces. You will no doubt notice how much slower Local is when compared to Planetarium mode. This is because DISTANT SUNS must do an additional rotation for each star in order to shift the perspective to your own frame of reference. Constellations The names of the constellations may be activated by selecting the "names" option. The same applies for the outlines. Each may be turned off by selecting the item a second time. Take note that generally the names are located away from the center of the constellation so as not to clobber important stars. The 12 constellations of the Zodiac are identified by the yellow names. Deep-Sky "Deep-sky objects" are those non-stellar entities outside of our own solar-system, such as galaxies, star clusters, and so forth. The "Messier" and "NGC" selections will display entries from two of the most popular deep-sky catalogs. The Messier catalog contains 110 entries, and the NGC or "New General Catalog" has over 10,000 listings of which the best 1967 are shown here. "Legend" opens up a window to aid you in quickly identifying the various types of objects. Extended Stars (not available in this demo) This will load in stars on demand from a more detailed file. The files will form a set of expansion disks, going down to about 10th magnitude, covering the entire Skymap database of over 250,000 stars. Since this database is about 20 meg in size, the user may purchase areas of interest, ("Vanna, I'd like to buy Orion"). To load these stars, merely zoom in to the area of interest, select the menu item, and the stars in and around the visible region will be loaded. These stars can take up a significant amount of memory, so using flushmem is recommended if you don't anticipate needing them anymore. Also, the dimmer stars are likely to be so dim you may want to either turn up the brightness of your monitor, or use a brighter colormap option, explained later. Field-of-View This selection will aid you in quickly moving to a particular field-of-view from 3 to 180 degrees. Besides this you can also use the buttons on the control-panel, or the drag-and-zoom option with the mouse. Landscape (not available in this demo) Landscape will turn on an artificial horizon to simulate mountains in the distance. With this activated, your vertical scrolling is limited to a range of +/- 20 degrees in altitude. You may adjust the landscape profile to match your own location, see the chapter on User Data for further information. Lookdown Lookdown will display a view of the solar-system from above. "Inner Planets" will show the orbits from Mercury to Mars. "Middle Planets" covers earth to Jupiter, while "Outer Planets" will show you Jupiter to Pluto. These selections act merely as macros to the off-earth mode (discussed below). That is, selecting the view of the inner planets is no different than if you were to move your eyepoint to 10 astronomical units directly above the sun, and then turn on the planetary orbits option. Markers The Markers menu will display additional information to aid you in further understanding how the stars are laid out in the heavens. "Altitude" will turn on an altitude line when in Local mode. This will show you the altitude above the horizon in degrees. The "ecliptic" denotes the plane of the solar-system based on the earth's own orbit. "Celestial equator" will display the projection of the earth's equator up against the sky. This is the imaginary line which separates the northern and southern hemispheres of the sky. The "horizon-line", shows your own horizon projected against the sky. In Local mode, it will be horizontal to the bottom of the screen. (It will be 5 degrees above the true horizon if the landscape is on.) In Planetarium mode you will see the line at an angle because your own point of reference is itself tilted due to your latitude. The "Grid" selection will overlay a right-ascension/declination grid on top of the stars, much like the grid in a star atlas. Move This permits you to move to a specific point in the sky, specified by either equatorial or horizon coordinates. The slider may be used to set the value, or you may type it directly into the text-box for more precise movement. The active "radio button" specifies which box the slider is bound to. When the slider is moved the text value is updated, along with the values in the alternate set of coordinates. That is, if you want to change the declination, click on its button that grab the slider. You will notice the declination value updating, along with the values for the altitude and azimuth. The right ascension will remain frozen. Search Selecting "antipode" will move your eyepoint to look directly "behind" your current lookangle. So for instance, if you wanted to find the earth's shadow, you could center on the sun and select this. (New to 4.1). The "by name" option will let you specify an object by its name to search for. (However the object must be loaded in order for it to be found. That is, if you are hunting for an NGC object, and the deep-sky objects have not been loaded, it will not be found.) When running the AmigaDos 2.0 version, you may use the standard Amiga wild-card convention. If you are running under 1.3, use a "*" instead. For instance, if you were search for the constellation of Andromeda, you could type "and*", and the "*" would effectively fill out the rest of the name. Hitting "return" will cause the search to take place. The "constellation" and "solar-system" selections will bring up a scrolling list of the possible selections. Simply click on the desired name, hit "ok" and the item will be centered. "Other" is a user definable search list. As with above, a scrolling list will open, but you may create the list of objects you have a special interest in. Unlike the above search operations, this list does not rely of loaded objects. Instead you specify the desired name, location and field-of-view. This way you can center on interesting parts of constellations or back out far to look at a large region. The next two menu items provide quick access to the Sun and the Moon, since these are likely to be the most commonly searched for objects. "Zenith" will point you to the location directly overhead. (New to 4.1). Viewpoint This is perhaps one of the most interesting features in that it permits you to move your eyepoint out from Earth and look back on the solar-system as a celestial traveller might see it. The "Earth" option is used to place your location back on earth. "Fixed" will put your eye at some fixed point in space, out to some 400 astronomical units (one astronomical unit, or "AU" is equal to 93 million miles, the distance from the earth to the Sun) away from the Sun or 10 times further than Pluto. The location of an object in the solar-system is typically given in "Heliocentric (Sun centered) Coordinates", measured in latitude and longitude. The heliocentric latitude is measured from the plane of the earth's orbit and the longitude from the "First Point of Aries". Both are expressed in decimal degrees and the distance in AU. The default setting is 35 degrees above the plane of the ecliptic, 0 degs from the First Point of Aries, and 10 AU from the Sun. Hit "OK" and stand back. Way cool, eh? Changing the latitude to 90 degrees will put you directly over the solar-system, identical to the lookdown viewpoint described above. The "other" selection will attach your eyepoint to an object orbiting the Sun. If the orbital traces are currently switched on you will see a number of gray lines crossing across the center of the screen. You can turn them off in the prefs window if you like. The objects own orbital trace is turned off, otherwise it looks strange when compared to the others. "Prefs" will allow you to fine-tune the scene : orbits - toggles on/off the orbital outlines. orbit dlines - this will render droplines from the object to the ecliptic. If the line ends in a green dot, the object is above the plane if red, it comes from below the ecliptic. The droplines are best seen on Plutos orbit or that of a comet. Since each orbit requires many droplines, this option will slow things up significantly. object dlines - this will render a dropline from each object to the ecliptic. As above green indicates the object is above the ecliptic, a red line, below. grid - this will draw a grid on the plane of the ecliptic, 10 units on a side. grid-size - changes the size of the grid (in AU) from .5 up to 20. ------------------- EXTRAS MENU -------------------- Earth's Shadow Renders the earth's shadow as a large round circle at the moon's distance. Useful mainly to demonstrate lunar eclipses. Lock "Select" will choose an object to lock on. This means that the object will always be centered no matter what. Hence none of the centering or move modes will work. This is most useful when producing animations, or when looking at an object over a long period of time saving you the trouble from having to re-center it. Object locks are not recognized when using the "fast" clock mode. In order to break the lock, select "release". Precession (not available in this demo) Normally no precession is performed on the stars, since it takes a long time whether it is needed or not. Selecting "auto-precess" will cause the stellar data to be updated if the date is changed by more than 200 years. The "stars" option will precess the stars on demand, should you require greater accuracy. Any extra objects such as deep-sky or user data, will also be precessed. So the more you're displaying the longer things will take. Normal precession ignores the outline data. In part a time saving measure, but this also permits you to compare the previous stellar positions with the new ones, by using old outlines. Sky-images A practically useless option. "Dynamic" (the default) will rescale the Sun and Moon images so they always present an authentic size for the given field-of-view (between 3 degrees and 30 degrees). If for any reason you feel the the images are too small for the wider fields, selecting "fixed" will scale the images for 15 degrees no matter how big or small the field is. This might be useful for auditorium demonstrations when the audience is far away from the display. Skylight (not available in this version) Selecting Skylight will make DISTANT SUNS attempt to duplicate the ambient light generated by cities or towns that wash out dimmer stars. In other words, if you live in downtown Cleveland, the sky will look a great deal different then it would from Buffalo, Wyoming. In fact, many people find it hard to identify constellations in a country sky because there are just too many stars. Star Data This option will place the selected data field alongside each star on the screen. One word of warning: Use a fairly small field, otherwise the data density could become so great, nothing will be readable. Also, the more stars on the screen the longer the process will take. A field wider than 30 degrees should be avoided when using the standard database, or 15 degrees when using any of the extended databases. Star Trails (not available in this demo) A persons first encounter with astro-photography is usually through the taking of stellar time-exposures with a camera fixed on a tripod. The results will produce streaks, or "star trails" caused by the motion of stars across the field-of-view. This phenomenon may be simulated by going into Local mode, setting the clock to automatic and increments to 5 minutes, and then enabling this option. Twilight (not available in this demo) The twilight mode is meant to simulate daytime. Turning on twilight will do different things depending on what viewing mode you are in. If you're in Local mode the sky will be a bright blue while the Sun is "up". As the Sun sets below the horizon, the sky will darken and the stars will begin to emerge. In Planetarium, since the Sun is always "up", the sky will be blue all of the time, unless of course, there is a solar-eclipse. Twinkle Selecting this operation will cause the stars to twinkle while you are on the Earth. If you're out in the solar-system there is no atmosphere to interfere with the starlight so they cannot twinkle. User Data (not available in this demo) The user may supply a custom list of up to 20,000 objects, which is loaded and displayed by this option. ------------------ PREFS MENU -------------------- Control Panel This will open the control-panel if it had been closed. Colormap-IF Depending on your specific needs you may want to change the colors of the interface. "Dim" and "red" are used to preserve the "night-vision" of an amateur astronomer who might have his/her Amiga propped up next to the telescope. Night-vision is when your eyes have fully adjusted to the darkness, maximizing their sensitivity. As it takes over 30 minutes to reach this state, astronomers are reluctant to use any lights during an observing session. When necessary, red lights are traditionally used. The "red" selection will turn everything in the display (except the stars) various shades of red. For the more aesthetically oriented observer, the "dim" option was added which preserves the colors, but merely darkens them. This has a side effect of changing the colors on the planets as well since they reference the same colors used by the interface. "Normal" will cancel the other options. Colormap-Stars "Bright" will increase the apparent brightness of the stars. You may want to use this if you are in a brightly illuminated room to make the stars easier to read, or if you are using an expansion database with many very dim stars. "Color" will display the stars in a variety of different colors to more clearly show the magnitude distribution. Crosshair Turning on the crosshair will pin-point the center of the screen. Info This will stamp basic information such as date, lookangle, etc, in the upper-left corner of the screen. You would normally use this when creating animations. Mouse-control This determines how the left mouse-button is to be used. The default is "point-and-center". By putting the pointer over a location of interest on the screen and hitting the left mouse-button, DISTANT SUNS will center that spot. The second mode is "identify". The mouse pointer will now change into a crosshair. By centering an object in the crosshair and clicking the left button, a data window will appear. Several windows may be displayed depending on what the object is. For a star you will see the normal data detailing the star's brightness, location, spectral type and so on. Some stars will have associated comment files which will give further notes, historical and otherwise. For deep-sky objects, in addition to the data and comment windows, you may see an actual image if you have the image-expansion disk. Two sample images are supplied, one for "M101" and the other for "M57". You will experience a slight delay when this mode is activated. DISTANT SUNS is redrawing the screen, but this time it is storing away the visible objects making this mode possible. This process will slow up a screen refresh, so use it only when needed. In order to see the images, turn on the "Messier" object list, DSO names, and search for M57. When centered click on it, and a data window will open along with a brief description and image. In the data window you will notice a button labeled "view". If unghosted, there are full-screen images available which may then be displayed by clicking on the button. For this demo, only a single image is included for this object only. In the full version of the software over 20 images are supplied on the third disk. The user may also add their own to any object and as many as desired so as to creating virtual slide shows for the moon, planets and deep-sky objects. Great for when the in-laws come over or for a school science project. The third selection for the mouse is "zoom". This will turn your mouse pointer into an angle-bracket and will permit you to zoom into a region of interest merely by drawing a box around it. Hold the left button down, drag the mouse to surround the area with the "rubber" box, and release it. You may not zoom any close than a 1 degree field of view. Show mag At times you may want to limit the displayed magnitude of the stars. The "show mag" window will let you do this. Merely select the dimmest magnitude you desire to display, and hit the "OK" button. "All" will reset the slider so as to display all of the stars. You may want to use this to limit the number of displayed stars if you are running on a slower machine. Cutting the magnitude down to 5 or even 4 will dramatically speed up operations. Then you can bring up the dimmer stars once you have the configuration you desire. Show objects "Planets" will display a window letting you selectively turn on or off any planets for display, along with the moon. This would be used mainly for two reasons. As with "Show mag" above, turning off unneeded planets will make operations faster if you were performing a "track" on a planet. Also, if you were looking back at the solar-system from some distant point, having all of the planets on may cause unnecessary screen clutter. Particularly if you are trying to produce an animation. "Other" will filter out miscellaneous objects. If you are interested only on solar-system operations you may want to turn off the stars completely with the "stars" item. If the names of the deep-sky objects interfere with each other you may want to turn them off by using the "dso_names" button. Finally, you may selectively turn off several classes of deep-sky objects, once again to remove screen clutter. Titlebar This will turn on/off the titlebar. If you are running under AmigaDOS 1.3, you need the titlebar to drag the screen down. Tracker "Animate symbols" will cause the planetary "symbols" (their dot and name if turned on) to be animated when using the fast clock animation mode. Those with slower machines may want to leave this off, in order to speed up operations. "Object droplines" is the same as the "object dlines" check-item in the OEV-Prefs panel. This will do nothing when you're eyepoint is on the earth. When off the earth, in in "fast" mode, the droplines will be rendered at each update, and left on the screen giving a unique perspective on the orbits. "Trails/lines" will cause the objects to leave lines in their wake, and "Trails/points" with do the same, but with dots at each update. -------------------- TOOLS MENU -------------------- Anim control (not available in this demo) This will open up a window on a separate screen to help you create an animation file. Chart The "Chart" function will display the entire sky as a Mercator projection. This will give you a sense of how the stars and deep-sky objects are distributed. The white-box outlines the general area displayed in the main screen. A small control panel will let you turn on/off the grid lines, stars, constellation names and the dso objects. Clicking anywhere in the window acts just the same as point-and-center does in the main screen, so chart may be used as yet another aiming device. Custom SS object "New orbit" will let you create or add a new object to the solar- system such as a comet or asteroid. (Not available in this demo). "Load" will load in a custom solar-system object. The more objects you have loaded, the slower the system will be, so use "unload" to remove any unneeded objects. Ephemeris An "ephemeris" will give you a location table for a desired object over a period of time. In the ephemeris window, select the object via the "object" button. Enter the range of dates and increments in days for how frequently the data is to be calculated. For the inner planets you would probably want to make this "1", for the outer-planets use longer intervals unless you need great accuracy. "Print" will dump the data to the printer, and "save" will save it to disk. Flashcard The "flashcard" tool will aid you in learning to identify the constellations. Turning on flashcard will switch off all of the identifiers on the screen, center the screen at a random location and challenge you to figure out just what you're looking at. The identifiers may be toggled with the "on" and "off" buttons in the flashcard window. "Flash" will turn off everything again and jump to a new location. Exiting flashcard will restore you to your original state. Mag window This will display a simple magnitude legend. Save to iff (not available in this demo) From time to time you may want to make a screen dump to take outside, or on a trip to use as a reference. "Save to IFF" will let you do this. The screen shot may then be loaded in your favorite paint program and then printed out. While in the program you may want to add any explanatory notes or diagrams. Tables "Tables" will let you create your own on-line reference system by displaying any simple text file in a listbox. With this you may want to add tables of upcoming eclipses, favorite variable stars, and so on. Two tables are supplied, one for the major meteor showers of the year, and the other for the Greek alphabet. What's Up? The What's Up? screen provides you with a simple quick overview of what's going on in the sky that night. Startup Configuration DISTANT SUNS will let you define your own startup parameter through the use of "ToolTypes" situated in the icon. On the boot-disk you will notice two DISTANT SUNS icons, one labeled "ds_4.1" and the other named "Halley's Comet". Click on this, and open up its "Information" window. (Under AmigaDOS 1.3, this is the "info" menuitem in the Workbench menu, and under 2.0, it is "information", located in the Icon menu.) In the window called "Tool Types" you will see a couple of lines which define the program's startup configuration. The RES argument specifies what resolution you want the program to run at. On a machine with only 512K of CHIP RAM (A500s or A1000s), you can only run in medium-resolution (non-interlaced) modes due the limited memory available. RES will be followed by one of three mode values, "med" for medium, "hi" for high-res interlaced and "over" for overscan. These resolutions cannot be changed once the program is running. If you are running on a PAL machine, the resolutions will be adjusted as required. That is, the "hi" mode under NTSC will be 640x400, while under PAL it will be 640x512. The use of a deinterlacer is recommended when running in interlace mode unless the flicker doesn't bother you. The other Tooltype, STATE, will cause the desired state file to be loaded. A state file contains all the information needed to set up the program to a certain date, time, location and option configuration. Therefore the state-file for Halley's Comet will jump you right to a view of the comet requiring no work on your part. Once in the program, it will operate normally. ORDERING INFORMATION : DISTANT SUNS 4.1 should be available at your local Amiga dealer by the time you read this for a "suggested price" of $99.95. DISTANT SUNS is also available for IBM and clones running Windows version 3. (Of course it is missing the options which are unique to the Amiga). Current owners may upgrade by sending in their original disk with $10.00 to Virtual Reality Labs, 2341 Ganador Ct., San Luis Obispo, CA, 93401. (805) 545-8515.