Undocumented features in Guide
The following features are either undocumented, or poorly documented. Some are simply not very useful; some would be useful, but are very confusing and no good, non-confusing interface has been designed (in such cases, suggestions are welcome... in fact, one reason I am posting data about these features is in hopes that someone will suggest ways to improve them).
Showing compass points on the horizon
It's quite possible to create your own objects to appear on the horizon, and/or to rescale, add, and move existing objects. People occasionally do this in order to get horizons that look a bit more like those seen from their observing locations. (Read the end of the file horizon.dat, in the Guide directory, for directions about how to do this.)
Those wanting to have large letters "N", "E", "S", and "W" on the horizon to label the compass points need only download this file to your Guide directory and unZIP it. This will replace the existing horizon and object files with ones containing the four large letters, plus some smaller triangles indicating the intermediate NE, SE, NW, and SW points, and still smaller indicators for the NNE, etc. points.
To return to the default horizon, simply delete horizon.dat and objects.dat from the Guide directory. Guide will automatically reload the original versions from the CD-ROM.
Viewing from probes, satellites, asteroids, and comets
This is something of a "work in progress", and will not be completed until after Guide 8 goes out the door. However, some interesting things can be done with it already.
Page 33 of the July 2001 issue of Sky & Telescope has a paragraph or two about the Pioneer 10 probe, now about 11.5 billion km (78 AU) from the Sun. It mentions that it is now "3 degrees north of the ecliptic, near the star 98 Tauri."
After considerable digging, I found orbital elements for this (and some other) probes, converted them to a format Guide could load, and added Pioneer 10 as an "asteroid". If you're running the 5 June 2001 or later version of Guide, you can hit Ctrl-B (or use "Go To... Object Name"), enter "Pioneer 10", and Guide will recenter on that object, which will indeed be found near 98 Tauri. I gave these probes the brightness level of a two-meter diameter asteroid, so you'll have to turn asteroids "on" (or to a very deep magnitude limit that might as well correspond to turning them "on") in order to get them to display. Pioneer 10 is currently shown by Guide as mag 51.
Similarly, you can view Pioneers 6, 7, 8, 9, and 11, Voyagers 1 and 2, Cassini, the Ulysses probe (now in an orbit at right angles to the sun), Giotto, and Magellan. Be warned that the positions will be erroneous for dates before these objects were launched, and will usually not be especially good for dates near planetary encounters. In most cases, I was able to turn up elements for a variety of dates ("use these elements for the Earth-Jupiter leg; these for the Jupiter encounter; these for the Jupiter-Saturn leg", etc.) Still, I'll have to turn up some better data for most of these objects. (And there are still plenty of probes for which I have no elements at all.)
Now we get to the "viewing from" part mentioned in the title. After you "go to" one of these objects (or to any planet, artificial or natural satellite, comet or asteroid, or right-click on any of these), hit the '<' key. Guide will reset your viewpoint to be from that object.
(A warning: before doing this, you probably want to turn asteroids Off. Guide can usually display 100,000+ asteroids with decent speed, but that's because it can use some precomputed info as to their visibility from Earth. Switch to an off-Earth viewpoint, and that becomes useless, and it takes much longer to compute it all.)
Obviously, I first used this to switch my viewpoint to Pioneer 10, and then looked back to see the Earth and inner solar system all reduced to a two-degree field of view, with the sun a mere half-arcminute in diameter (you would probably see it as a very bright point, rather than a disk). I then set the date to November 1973, the time of the Jupiter flyby, did a "go to" Jupiter, and started animating, getting a nice view of Jupiter growing from a small disk to a bigger, gibbous disk, and finally receding as a crescent.
As you might expect, you can get similar views of other planetary flybys, especially from Voyager 2, the only probe to visit all four gas giants.
As mentioned above, you can also reset your viewpoint to be from any other solar system object. When I added this feature, the asteroid 1999 KW4 had just passed close by the Earth (late May 2001); I did a "go to" 1999 KW4, hit '<', and looked back at the Earth. Much as with the planetary flybys, you can do an animation showing what an observer on that asteroid would have seen.
You can also set your viewpoint to be from a satellite. There are limitations to this; get too close to the Earth (or any other planet), and Guide will refuse to display that planet; the perspective effects get to be a bit of a problem (something I may get around to fixing someday; it didn't matter much before now, but it would be very nice to get an "out-the-window" view from the ISS...)
As a very nifty and educational example, use Ctrl-B (or "Go To... Object Name") and enter "Molniya". (Click here for a discussion of Molniya satellites.) If this doesn't "go" anywhere, your current satellite data file lacks any Molniya satellites; you should probably use Settings... TLE=, and click on the "Molniya" link given there. Guide will then download current orbital data for the Molniya satellites. Then try finding "Molniya" again, and it should work.
Once Guide "finds" it, hit '<' to switch your viewpoint to that satellite. Set a wide field of view, say, level 3 (45 degrees), and "go to" the Earth.
Start up the Animation dialog, and set the time step to about 15 minutes. Select "Moving" (i.e., Guide should stay centered on the moving target, now selected to be the Earth) and start animating.
For most Molniya satellites, you will see the effect of the very eccentric, twelve-hour orbit quickly. You will see that, each twelve hours, the satellite zips rapidly past the earth, then climbs up to a very high orbit over latitude 65 degrees north. It then seems to just hang there, the motion of your viewpoint staying in synch with the rotation of the earth, for about eight hours out of the twelve-hour cycle. You get a little farther away, then a little closer, but the same part of the earth sits under you. And somebody sitting on that part of the world would see you in the same part of the sky... much like a geostationary satellite, which is the whole point of being in this sort of orbit.
You'll also see that, because the orbit is a half-day one, you alternate 180 degrees in longitude in each orbit (usually, one orbit is high over Russia, the next is high over Canada.) A few satellites instead go high over the Southern Hemisphere, and apparently are either off-course or intended to look at Australia, South America, and/or South Africa.
The view from a properly-maintained geosynchronous satellite (elements for these are available at the above site in the GEO file) is less interesting: you just see the earth sitting still, going through a complete set of phases once a day with stars drifting past it. If you select one that has been left to drift, you'll see the characteristic "figure-eight" curve of such a satellite: it drifts north/south once a day, and east/west twice a day, so you see the earth rock back and forth a little.
When you're done and wish to return to an Earth-based viewpoint, you can 'go to' the Earth (or right-click on it) and hit '<' again.
Adding new features to solar system objects
As of 8 April 1999, you can label craters and other features on the Moon and Mars, get lists of such features, and tell Guide to recenter on them; click here for details. Some people will want to add features to other planets, and/or revise the features for the Moon and Mars.
The feature names for the Moon and Mars are stored in PLANET10.GAZ and PLANET04.GAZ, respectively; edit either with a text editor, and the format should be apparent. For each feature, a lon/lat and name are given. For craters, the first character in the line is 'C', followed by a diameter in kilometers. For example,
-019 +27 SERENITATIS -087 -02 SMYTHII -065 +01 SPUMANS -031 +09 TRANQUILLITATIS C 84 +011.2 -43.3 Tycho C 82 +004.0 +29.7 Archimedes C225 +014.4 -58.4 Clavius C 93 +020.0 +09.7 Copernicus
Ideally, the features should be in order of importance, and I have moved a few objects to the top of the list to make this happen. Thus, Tycho is drawn before surrounding smaller craters; otherwise, after the smaller craters were drawn, there might not be room to draw Tycho.
One defect in the lunar data (PLANET10.GAZ) is that I'm no lunar expert. I moved the maria to the top of the file, since they are the most prominent features on the moon; and moved about a dozen really prominent craters to the top of the file. After this, craters are just listed in decreasing order of size.
Features on the Sun (sunspots, I suppose) would be in a file of the same format called PLANET00.GAZ. Mercurian features would be in PLANET01.GAZ, Venerian features in PLANET02.GAZ, and so on, to Plutonian features in PLANET09.GAZ. Ionian through Callistan features would be in PLANET11.GAZ to PLANET14.GAZ. Features for Mimas through Iapetus would be in PLANET15.GAZ through PLANET22.GAZ.
Display of solar system objects from viewpoints other than planets
One minor annoyance in Guide can be that you can't (for example) pick a viewpoint a few million km above Jupiter, look back at it, and watch the Galilean satellites orbit... or pick a viewpoint 20 AU from the Sun and look back at the asteroid belt to see it as a tilted, flattened-doughnut shape... or pick a viewpoint a few radii from the Moon, then look back at the Earth "rising" over it. There actually is a way to do this (recently added in the update files). But it is horribly confusing!
Take the Jupiter example first. Select Jupiter as your "home planet" and look in the direction of Octans (close enough to the south pole of the ecliptic for our purposes). Back out to level 4 (20-degree field of view). Right now, your viewpoint is exactly at the center of Jupiter. Our next step will be to "back up" our viewpoint by 15 million km, or about .1 AU.
To do this, hit Ctrl-F5. You'll be prompted to "Enter offset:" Enter an offset of .1, and Guide will redraw, with Jupiter at the center of the field and the satellites clustered around it.
Start animating, and Jupiter will stay fixed (rather, you will continue to "hover" .1 AU from Jupiter), and the satellites will be seen to orbit Jupiter. Stop animating, hit Ctrl-F5 again and enter a zero offset, and your viewpoint will revert to the center of Jupiter.
Each time you enter a non-zero offset, your viewpoint will change to one that is a particular distance from the home planet, in the direction opposite to the one currently at the center of the screen. Your viewpoint is fixed to the stars and does not rotate with the planet; for example, if you have Capella at the center of the screen and enter an offset value, the planet will block Capella from view and will continue to do so, no matter what date/time you set, until you enter a new (or zero) offset with Ctrl-F5.
Adding your own notes
There are already a few examples of "user notes" provided. Edit the file PLANETS.NOT for a good example. I've used the "note file" feature here to give a brief description for each planet. You'll see that the format is quite simple; each note is prefaced with the object number, followed by free-form remarks. Glossary terms are enclosed in carets; you can add your own glossary terms to the file EHELPEXT.DAT with little difficulty. When you click for more info on a planet, the corresponding notes are fetched from PLANETS.NOT and shown.
Aside from revising PLANETS.NOT, one can create files in the same format called NGC.NOT and IC.NOT, and use the same system of object number followed by notes. Also, one can create files called PGC.NOT, UGC.NOT, NSV.NOT, GSC.NOT, BSC.NOT, PPM.NOT, HD.NOT, WDS.NOT, and SAO.NOT (and, very soon, there will be an ASTEROID.NOT, VARIABLE.NOT, and COMET.NOT)
Loading marks with a hotkey and/or toolbar button
This feature was added recently to Guide 8. It is quite powerful, but decidedly not for the faint of heart. Here's how it works:
Hotkeys and toolbar buttons in Guide work through a set of "action codes" (click here for details). For example, code 61 corresponds to "go to PGC galaxy"; when you tell Guide to execute that action code, via either hotkey or toolbar button, that function is executed. Almost all of the action codes are listed in the file toolbar.dat.
There are at least a hundred action codes not listed in that file. These are codes 9800 to 9899. Those action codes cause Guide to load the mark files mark00.txt to mark99.txt. The simplest way create a mark file is to set up Guide as you desire, then go into File... Save a Mark. When you do that, Guide creates a file of extension .mar. Look in Guide's directory, find that file, and you can rename it to (say) mark17.txt.
Having done this, you can now edit toolbar.dat and increment the number of available toolbar buttons, given at the top of the file. Then add a line for the new action code:
9817 !17.bmp Load up the mark I just made
Start up Guide, and you'll see that there's a new button on the toolbar. Click on it, and Guide loads up the mark file. Go into Settings... Toolbar, and you can toggle that button and/or select a hotkey to go with it. Create a new .bmp file and put its name in place of "17.bmp", and Guide will show it on the toolbar.
One problem with all of this is that the mark file will usually contain all sorts of extraneous junk. Getting rid of that junk is possible; you can read about the .MAR format here. With that knowledge, you can pick out the lines that actually matter to you. For example: suppose I wanted a file that just had the lines setting my latitude/longitude and time zone. I might create, say, a mark17.txt file that contained the following lines:
999 name Bowdoinham, Maine 11 lat/lon 69.9 44.01 0 15 timezone -5.000 17 zonename EST 20 home 3 28 altitude 30.00
This will set my latitude/longitude to W69.9, N44.01; my time zone to UT-5 (Eastern Standard Time); my "home planet" to be the third one from the sun; and my altitude to be 30 meters above sea level. I sometimes set up alternative locations (say, a customer asks me about a problem involving an object as seen from her location, or I want to see what Mars looks like from Phobos). I could recover from this by using "File... Load a Mark... Initial position", thereby putting myself back where I was when I started the program; but if I just want to reposition myself without changing other settings, I can hit the '17' toolbar button (or the hotkey I've associated with it: 'h', for 'home') and suddenly see the universe as it appears from Bowdoinham.
Putting Telrad symbols into overlays
Normally, one gets a grand total of exactly one Telrad symbol to use in Guide. It can be toggled on and off, and stays in the center of the field of view as you pan around the sky.
If you're editing an overlay, you can add a Telrad symbol to that overlay. Select "Add text" from the Overlay menu, and click on the point where you want to put the Telrad. Normally, you would type in some text to add to the current overlay. But instead, type in the text "~tel".
Guide will interpret those four characters as a special command, meaning "instead of putting text here, put a Telrad symbol here". Using this, you can drop Telrad symbols anywhere you want, in any desired quantity. I've regarded this as being a mostly useless capability; if people tell me otherwise, I'm open to turning it into a menu option.
Modifying the display of variable stars by class
This actually is "documented", loosely speaking; check the file \COMPRESS\VAR_TYPE.DOC on the Guide 5.0 CD. This provides a way to (for example) show all Mira stars in red, at a magnitude that is 2/3 of the way from minimum to maximum. For example, one might want to show cataclysmic variables and flare stars at minimum magnitude, because they spend almost all their time at minimum except for the brief days when they erupt. On the other hand, eclipsing binary stars are almost always at maximum, with a short brightness drop when they are in eclipse; therefore, one might reasonably wish to keep them at maximum brightness.
Some variable enthusiasts might also wish to shut off some classes of variable stars, or display them in a color-coded manner. All this is described in considerable detail in \COMPRESS\VAR_TYPE.DOC.
Modifying data shown in Quick Info
By default, Quick Info shows a "reasonable" amount of data, such as visible asteroids to mag 11, visible comets to mag 15, and one month of lunar phase information. To alter these default values, edit the file STARTUP.MAR. One line will read
61 quickinf -1 110 150 1 0 0
The '110' refers to the mag 11 limit on asteroids. It's followed by a '150' (mag 15 limit for comets), '1' (one month of lunar phase data), '0' (show zero days of Jovian satellite events) and '0' (reserved for future use). These values can be modified to (for example) have Quick Info make a massive list of comets to mag 17, but ignore the lunar and asteroid info; or to make a list of Jovian satellite events for the next two years.
(DOS only) Full-screen cross-hair
I added this feature long ago and completely forgot about it, until a Guide user e-mailed me that she had stumbled across this feature and liked it, and would I please add it to the Windows version? The feature in question shows up in DOS when you hit Alt-F8; the cursor changes from the "small cross-hair" to a "full-screen" cross-hair. It's slightly helpful for night use.