FAQ for Guide users
The following are the most commonly asked questions about Guide from users of the software. People who aren't already using the software (prospective new users, for example) usually have very different questions; click here for the FAQ for people thinking about purchasing Guide. There is also a list of rarely-asked questions on this site.
Q: How do I reset the longitude of Jupiter's Great Red Spot?
A: In Guides 1-8, there was a menu option to reset the GRS longitude, to account for the fact that (like most clouds, on Earth or Jupiter) the GRS moves. In Guide 9 (and in the updated versions of Guide 8), that option is gone. Instead, GRS longitudes for various dates are stored in a file. To update it, save this file :
in your Guide folder. It should overwrite an existing copy of grs_lon.txt. (If it doesn't, you haven't saved it in the correct place, and should try again.)
The reason for this change from previous versions of Guide is described at the end of grs_lon.txt, copied here:
At one point, the GRS longitude in Guide was set by the user. But the GRS moves; what is really needed is a table giving the GRS longitude as a function of time. That way, when you ask Guide to show you Jupiter as it was in 1977 or 2003, the GRS will be correctly located, and transit times will be computed accurately. This file provides that table. Guide computes the System II GRS longitude for any date by interpolating within this table. Data are given from most recent to oldest. For each date, a year, month, day, and System II longitude are given, followed by the source of the data. For dates after the most recent data point, the last GRS longitude is used; for dates preceding the table, the oldest GRS longitude is used. Note that, while coverage is good for years since 1986, the data gets a little sparser for previous dates. The GRS longitude currently appears to be increasing at about 14 degrees per year (with plenty of fluctuations). That amounts to about 700 degrees over 50 years; so I've taken the most recent data point, added fifty years and 700 degrees to it, and added it as an extrapolated value. This is just to get around the fact that otherwise, the GRS would remain at the last listed value, which is almost certainly even less realistic than the assumed drift.
Q: I'm running into problems installing or running Guide on Vista or Windows 7.
A: Guides 7 and 8 were released before these two systems existed. The transition was mostly smooth, but some have found that the Setup program failed or saw problems when actually running the software. To the best of my knowledge, all of these problems are now fixed. You can click here for details on how to get Guides 7 and 8 to run in Vista or Windows 7.
Q: I've got a strange object/objects/lines/whatever appearing on screen. How do identify it and/or turn it off?
A: You can right-click on almost anything on the chart and get an identification of it. (There are a few exceptions, but this will work about 99% of the time.) The result will be the usual small dialog box with some description of the object you clicked on, and most of the time, there will be a "Display" button in the dialog.
Clicking on that button will get you some control over the display of that type of object. Exactly what sort of control varies somewhat, but you usually can turn the objects on or off, set a limiting magnitude (either "fixed" so it doesn't change when you zoom in or out, or "auto" so you see fainter objects when you zoom in), colors, and labelling of the object.
This is an important feature to keep in mind. Guide shows a long list of objects, and it isn't always as easy as it might be to figure out which menu options to go through to control object type X. But if an example object is on-screen, it becomes much simpler: click on that object and then on "Display."
Q: I'm getting odd planetary/comet/asteroid positions... why?
A: In general, Guide's positions will be within the (very stringent) error limits given in this discussion of solar system precision. People often report position errors; the reasons usually boil down to the following:
Q: How do I get features to appear on planets?
A: You will need to download the current version of Guide from the Web site. You'll also have to download the PLANETS.ZIP file (about 580 KBytes), and unZIP it in your Guide directory. This contains the list of planet feature names, plus some new planet bitmaps.
Once you have done this, though, the features will still be shut off by default. You should zoom in on the object for which you want to see features. Then right-click on it, select "Display", and select "Options." You'll get the planet display dialog for that planet, which has a box to turn the features on. (It will also allow for display of a lat/lon grid on the planet, plus control over which bitmap is used when displaying it.)
Q: When I click on the "DSS via Internet" button, I don't get an image.
A: There are several things that can go wrong here. First, in theory, this function should establish an Internet connection if one does not already exist. That is, if your modem isn't dialed in when you click on this button (or on the similar "download A2.0 data" and "download GSC-2.2 data" options), your modem should emit the usual noises and chirps as it establishes the connection.
In practice, this does not always happen. If so, you will have to first establish the connection manually, then select the download DSS (or A2.0, or GSC-2.2) options. Most failures to get data in Guide via Internet are solved by doing this.
People running Guide 7.0 sometimes find that this solves the A2.0 and GSC-2.2 problems, but not the DSS problem. That usually means they are lacking the GZIP386.EXE file needed to decompress the DSS images. You can click here to download GZIP386.EXE (about 92 KBytes). Put it in your Guide directory, and the images should appear. (Guide 8.0 users can ignore this; for them, GZIP386.EXE is provided from the CD-ROM.)
If, despite doing this, the images still do not appear, check the other options in the "Extras... DSS/RealSky Images" box. Are the images turned on? Are you at a field of view where they are shut off? (By default, Guide shuts off these images for any FOV of about 1.6 degrees or greater.)
The final cause of trouble is a very basic one that's hard to evade: sometimes, the server for DSS and GSC-2.2 (at the Space Telescope Science Institute) is down. In such cases, you may be able to access A2.0 data (which comes from a European Southern Observatory server), but not the other two. When that happens, the only solution is to wait a little.
Something that may be worth trying: recent updates to Guide 8.0 include options for accessing DSS-2 images. At the same time these options were added, the error handling was beefed up a bit. It used to be that some errors resulted in no message at all; Guide would simply sail along as if nothing had happened. With the new version, you will get error messages in such cases.
Q: How do I get Guide to read RealSky (or DSS) data that has been copied to a hard drive?
A: Suppose you've copied over one or more RealSky (or DSS) CD to your hard drive, under a folder such as c:\realsky. When you fire up Guide and use Extras... DSS/RealSky Images... RealSky/DSS from CD, you'll see a "Drive:" edit box. Enter c:\realsky\ in this dialog (note that the trailing backslash matters!), and Guide will look for RealSky and DSS data in that path, instead of the (default) CD drive.
There's only one problem with this: the next time you attempt to extract an image, Guide will have "forgotten" that you entered this path! I hadn't really planned ahead for this possibility. To make a permanent change of path, you must edit the file environ.dat in the Guide folder, and look for a line such as
and change this to something resembling
(again, the trailing '\' matters). You must then also set environ.dat to be read-only; if you don't, Guide will clobber the change you've made.
Q: How do I uninstall Guide?
A: At some point, I will probably add an uninstaller for this. But right now, the way to do it is simply to delete everything in the Guide directory (usually, c:\guide8). Guide puts nothing in the Windows registry or Windows file system, so just getting rid of the directory will eliminate any trace of Guide on the system.
Q: I've loaded some RealSky images, and/or downloaded DSS images; how can I alter their contrast and brightness?
A: There are three ways to do this.
For all of them, the first step is to right-click on a corner of the image you want to adjust. You'll get a short dialog box describing the image, plus a comment such as "Contrast: 1500 to 12000". This means that a pixel value of 1500 is shown as pure black, one of 12000 as pure white, and shades of gray are used in between.
The first undocumented way is to use four hotkeys. Alt-Up and Alt-Down increase and decrease brightness. Alt-Right and Alt-Left increase and decrease contrast. This is probably the simplest method. The same technique works when you've just right-clicked on a planet; in each case, the right-click is necessary so that Guide will know exactly what it is that is being contrast/brightness adjusted.
These keys are also discussed here.
The second way is to go into the "Settings... Toolbar" menu. About 80% of the way down the list of toolbar buttons, you will see "Increase Contrast", "Decrease Contrast", "Increase Brightness", and "Decrease Brightness" toolbar buttons. Turn these on, and you can click on the toolbar buttons instead of using hotkeys.
The third, alternative way is to hit Shift-F8. You'll be prompted to "Enter filename:" Instead, enter (for example) "3000,8000". The result will be that the range in which gray-scales are used will be narrowed a bit; i.e., contrast will be increased. Similarly, "1000,10000" would brighten the image; raising both numbers, such as "3000,18000", would darken it; and so on.
Q: I'd like to replace Guide's built-in asteroid data with a current version of ASTORB. How do I do this?
A: The short version is: you can't. Several people have noticed the ASTORB file in the ASTEROID directory of the Guide CD, and assumed that by somehow replacing this, they could update the data. This is not true, for the following reasons.
The ASTORB data is indeed used to generate the initial data. But it is numerically integrated to produce the 140-odd megabytes of orbital data on the Guide CD. This precomputed data takes a few nights to generate, but is the reason Guide can instantly provide good positions for 30,000 asteroids over a long time span... all the "heavy lifting" has already been done. It also precomputes maximum magnitudes and some other data used to allow it to completely disregard most asteroids on a given chart. If you only ask, say, for magnitude 13 asteroids in a five-degree chunk of sky, it can quickly dismiss about 99% of the asteroids from consideration, without doing very much math.
By the way, you can see how much this helps by setting a "home planet" other than Earth. In such a case, the precomputed maximum magnitudes and such become useless, and Guide has to do all the math for every asteroid. Even on a fast PC, this is a real drain on system speed.
You can switch to use of the MPCORB database. This is available via the Minor Planet Center Web site, and offers some advantages over Lowell's ASTORB database. The main drawback is a lack of speed. That's not the fault of the Minor Planet Center; it's just that all the precomputed optimizing that's done for the data on the CD-ROM hasn't been done for the MPCORB database.
Q: In Guide 6.0, the nebula outlines for Northern nebulae look wonderful. But when will there be outlines for Southern ones?
A: The Northern nebulae on the Guide 6.0 CDs were generated using RealSky North data. At the time, RealSky South hadn't been released yet. Guide gets a lot of use in Australia and New Zealand (and an increasing amount of use, recently, in South Africa and South America), and users there have been quite vocal about the omission of 'their' nebulae (particularly the Magellanic Clouds).
The distributor for Guide in Germany, Eric-Sven Vesting of the Astro-Shop in Hamburg, has created the southern isophotes, and they are provided on the Guide 7.0 CD-ROMs. (I'll have to admit that they aren't quite perfect. The great problem is that the southern plates in RealSky are in blue light, not red, and the nebulae just aren't as obvious. We did get all the major objects, though.)
Q: I want to run Guide from my hard drive. How can I do this?
A: This was once a real pain to do, but is now quite simple. Guide 7.0 users should read these instructions. Guide 8.0 users should look at chapter 17c of the user manual.
Q: I'm finding that, on printouts, smaller stars are omitted, and/or that 'outlined' stars aren't outlined.
A: This problem is sometimes seen in the Windows software, on some HP printers (occasionally, in others). It usually shows up only in Landscape mode, with fainter stars completely dropped out. It is due to a bug in the printer driver, and there are three possible fixes to it.
First, you can get an updated printer driver. This (usually) causes the problem to go away (though not all printer manufacturers have fixed this bug yet).
Second, if you prefer not to use the latest printer driver, you can run Guide and hit Alt-J. This will bring up a dialog box asking you to "Enter test flag number:" Hit 'c' and click OK. The result of this will be to cause Guide to use a different printer function to print small stars... and this different function does work correctly, without bugs.
You may wonder why this option exists. The answer is that, when working on star display in Guide, I wanted an easy way to test several different ways of plotting stars. So I added this "hidden" option to easily switch methods. The usual method for plotting small stars is faster and produces better stars (the shape is more regular), but I never did get around to removing the old code... a good thing, as it turns out.
And the third solution is to print in Portrait mode instead. It's not much of a solution, but it's one to keep in mind if you don't want to try the first two.
Q: Guide persists in printing in B&W, even though I've got a color printer.
A: You probably have not gone into the Display menu, selected "Backgrounds", and chosen "Chart Mode". In Chart Mode, Guide switches to a white background, and you can set up the colors that will be used for color printing. Once you have things exactly as desired, you can print, and Guide will do so using the same colors you see on the screen.
Switching back to "normal colors" will cause you to return to B&W printing.
But the DOS version of Guide prints only in B&W. There is little I'll ever be able to do about this, I suspect. (I have vague ideas of making color PostScript files, then running them through a GhostScript utility to handle the actual printing. But I can't say it's much more than a vague idea.)
Q: On some zoom level N, I'm finding that Guide shows me incredible swarms of stars; levels N-1 and N+1 are OK.
A: A few people have become confused about this. The Settings menu provides two level-related options. One lets you reset the zoom level you're on; you can go, say, from level 5 to level 15, and so on.
The second allows you to set the field of view associated with a particular level size. For example, were you at level 9, this option would usually read, "Level 9: 1 degree".
You can then use this option to reset the level sizes. You can go, say, to level 7, click on the menu item (which will read "Level 7: 2 degrees" by default), and reset the field size to, say, three degrees. The problem arises when one assumes one is entering a new level number rather than a new field of view. Someone will go, say, to level 9, click on "Level 9: 1 degree", and enter "13", assuming this will result in going to level 13.
Instead, of course, they stay at level 9, but draw a chunk of sky 13 degrees across. The result is billions and billions of stars... at least, at level 9.
There are four solutions. First, you can just click on "Factory Defaults" to get reasonable values. This will reset everything to factory default values, though, including your latitude/longitude, time zone, display preferences, and so on. The second solution is to go to the level in question, click on "Level ##: ## degrees" again, and set it back to a sensible value.
The third solution is to download this file to your Guide directory, then fire up Guide and go to File... Load a Mark. You'll see a new mark called "Default level sizes". Select this mark, and the level sizes will go back where they started.
The fourth solution is to get the current Guide software from the Web site (which I'd recommend doing anyway). There, you can click on "Level ##: ## degrees", and see a re-designed level size dialog box with 20 edit controls, one for each level. This lets you see all level sizes at once, and you can then fix the "problem" level(s) easily, setting them to the size(s) you actually want.
Q: Can I use Guide with the Tech 2000 Dob Driver?
A: Right now, no.
Quite a few people have been asking about this system lately. I am rather enthusiastic about it myself; I have a 13.1" Dobsonian that I'd like to configure with it. As I envision it, one would hook up the Dob Driver to a PC, and start up Guide. At first, one would only have "arrow" commands in Guide to push the telescope around; using this, you could align on two stars. With this done, you could then have "Go-To" capability (find an object in Guide, then click on the "Slew Telescope" command, and the Dob Driver would slew there.) Also, Guide could then track the object in alt/az.
Based on the literature from Tech 2000, makers of the Dob Driver, it seems that their "Roboscope" system won't be needed for this. Guide will control the motors almost directly, through a parallel port connection. (In a way, this resembles the Mel Bartels ALTAZ approach, except that the Dob Driver does have some more sophisticated electronics built into it.)
Given some more alignment stars, Guide could correct for mechanical errors, resulting in excellent pointing accuracy (as long as the errors are 'consistent'; the errors would have to be fairly repeatable in nature. Fortunately, most pointing errors, such as flexure, non-perpendicular axes, non-level mounts, off-axis bearings, and so on, fall in this category.) Periodic error correction should be straightforward as well. In theory, if the motors hold up well under higher speeds, tracking of artificial satellites at high magnifications ought to be quite possible.
For imaging, field rotation will be an obvious concern. You can get around this, to some extent, by taking short exposures or by imaging near the east-west meridian, but it's still a problem on alt/az scopes. My hope is to add commands for a field de-rotator motor and to persuade Tech 2000 (or _somebody_) to build such a motor commercially. (I'm very adept with software, but my knowledge of hardware is not good.)
This really looks like a promising direction to me. A few years from now, with cheaper laptops/palmtops, I can see it being possible that the current LX-200/Ultima approach, involving putting a lot of complex hardware on the telescope, will be replaced with a Dob Driver approach, where the hardware is pretty stupid (and cheap) and is controlled by suitably elegant software.
When Dob Driver support is added to Guide, the updated software will be posted on the Project Pluto WWW site.
Q: Can I use Guide with the Meade Magellan I or II?
A: No. The major problem here is that Meade is unwilling to provide the command language used to control these devices.
I have heard rumors that these devices are somewhat compatible with the LX-200, except in two regards: none of the 'slew' commands work (since these devices lack motors), and they run at 2400 baud (the LX-200 runs at 9600 baud). If these rumors are true, you can do the following. Edit the file STARTUP.MAR in any text editor, and look for this line:
49 lx delay 15 100 9600
(The '15' and '100' may be set to different values on your system.) Change the '9600' to '2400' and save the file to disk.
Now start up Guide, go into "Settings... Scope Control", and tell Guide you have an LX-200. Set the COM port radio button to match the serial port to which the Magellan is connected.
When you close the "Scope Control" dialog box, the commands "Slew Guide" and "Slew Telescope" should be added to the top of the menu bar. The first should work correctly: point your telescope at a given object and click on "Slew Guide", and Guide will point to that object. The second command will probably do absolutely nothing.
If you try this, please e-mail me and let me know what you find!
Q: I can't persuade Guide to print tables and 'more info'. What's going on?
A: This seems to happen, sometimes (not very often), usually on printers that are "Windows-only" (GDI) printers. To fix this, get the current software which contains a fix to the problem.
Q: Why is Xi UMa missing in Guide 6? Does it appear in Guide 7?
A: It does indeed appear in Guide 7. The problem was that there are 263 stars that are listed in the Hipparcos catalog, but not in the Tycho catalog. (The only really noticeable one is Xi UMa. After Xi UMa, the next brightest cases are companions to Xi Sco, 94 Aqr, and SAO 95765. No one mentioned noticing their absence in Guide 6, but they are not as blatantly obvious; the bright component of each double is still visible.)
In Guide 6, I naively assumed that no bright stars would be omitted from Tycho. For Guide 7, I knew better, and the 263 stars in question were added to the database.
The 263 stars omitted from Tycho appear to be double stars, companions to double stars, and cases where the Tycho instrument on the satellite was unable to accurately measure its position.
Q: I can't get the USNO SA1.0, and/or A1.0, and/or SA2.0, and/or A2.0, data to show up in Guide.
A: First major point: if you're using Guide 5.0 or 6.0, rather than the current 7.0, you may find it nearly impossible to get A2.0 or SA2.0 to load from CD-ROMs. (Displaying A2.0 or SA2.0 data that you downloaded from a Web site should be easy; just get it in binary form and save it under the name A10.DAT, and Guides 5.0 and 6.0 should be able to read it without difficulty... the data format didn't get changed, and Guide can't even tell the difference.)
Getting Guides 5.0 and 6.0 to run with A2.0 CDs is essentially a lost cause, because USNO rearranged the data across CDs. Guides 5.0 and 6.0 will therefore ask you for disk #X, unaware that, on A2.0, that data was moved to disk #Y. SA2.0 with older Guides is not so daunting; just download this file (about 12 KBytes) , unZIP it in the Guide directory, and (for Guides 5.0 and 6.0 only!) rename the file SA20.IDX to SA10.IDX. (You may need to delete an existing SA10.IDX to do that.) Once you've done that, you should be able to use an SA2.0 data in place of the SA1.0 data. (Be aware that Guides 5.0 and 6.0 will still be referring to "A1.0" and "SA1.0". You haven't really made the software understand SA2.0; you've just cheated it into thinking it has an SA1.0 CD.)
With that out of the way, the following comments apply to users of any version of Guide who have loaded up SAx.0 or Ax.0 data and wondered where all the new stars are:
Q: When I run Charon, I get a "Stub exec failed" error message. What can I do about this?
A: My apologies for this error... fortunately, it is easy to fix.
The WATCOM directory of the Guide CD has a file called DOS4GW.EXE. Copy this to the Guide directory on your hard drive, and the problem will go away.
In Guide 6.0, this file was always copied over when you installed Guide, because the DOS version of Guide needs it, too. But in Guide 7.0 and 8.0, if you don't install the DOS version of Guide, DOS4GW.EXE is never copied... and this is not a problem, until you try to run Charon!
Q: When I try to "Make a .BMP file" in Guide, I get no .BMP file or a garbage one.
A: This has happened to maybe half a dozen people so far. It appears to be due to a defect in 32-bit Windows: BMPs must be created using certain rarely-used functions from the video drivers, and those functions are generally not tested as carefully as we might wish. In some cases, you can evade the problem by switching to a different video mode (ideally, with a different number of colors used); when you do that, different functions in the video driver will often be used, and you will "evade" the bug.
Also, there are two other ways to work around this bug.
Also, Christopher Henderson, a Guide user in New Zealand, has pointed out that one can also get an image in the following way:
Here is a way to make a non-corrupted .bmp file in Windows 95. Get the place in the sky that you want in Guide. Press the Print Screen button on the top right of your keyboard to copy the screen shot to the clipboard. Paste the image in the clipboard into any image editor eg Paintbrush. The menu bar will be present in the image, but you can just cut and paste to remove it. Also, Paint Shop Pro 5 from Jasc Software (http://www.jasc.com/) can open the save .bmp files without any problems.
Len Philpot has suggested using Alt-Print Screen instead. This should capture the chart area only (instead of the chart plus menus plus title bar). He also points out that Paint Shop Pro has some good "capture" tools (and in fact, I often use these instead of the Print Screen and Alt-Print Screen keys.)
Q: Why is the horizon at a strange angle?
A: To make the horizon "level", go into the Inversion dialog. (You can reach it from the Display menu, or by clicking on the "N/E" compass symbol in the legend, or by hitting Alt-I.) The "RA/dec (north at top)" radio button is probably selected (it's on by default). Switch to the "alt/az (zenith at top)" button, click OK, and the chart will rotate to make the horizon level.
By default, Guide shows the sky the way a star atlas would. In star atlases, celestial north (the direction to the north star) is always at the top of the chart. That direction will usually be at some angle to the direction toward the zenith, resulting in the rotation you're seeing. This is not unlike the way that most terrestrial maps put north at the top of the chart, despite the fact that (as Murphy's Law makes clear) you're usually going somewhere between southeast and southwest.
Alternatively, you can toggle between "north up" and "zenith up" by simply hitting Alt-Z.
Q: I accidentally put Guide into a language I don't understand. How can I get it back to English?
A: Hit the '!' key twice.
The '!' key causes Guide to switch to French. If you are already in French, it will switch to English. (This lets French-speakers use it as a French-English toggle.)
Q: The rise/set/transit times I get when I click on the Moon don't make sense to me.
A: In quite a few programs, when you ask for rise/set/transit data for an object, you get the times that object rose, transited, and set on that particular calendar day. In the case of the moon, on about 10% of calendar days, one of these events will not occur at all.
Guide does things a little differently. When you click on an object, you get the time of the nearest transit, the preceding rise time, and the following set time. This has several benefits. The events are all shown in chronological order. With the "usual" scheme, if the moon rises in the evening and sets in the morning (as happens around full moon), the order of events can be a little weird. Also, the "usual" scheme can keep you from seeing that an event is about to happen (or just happened), but on the following (or preceding) calendar day.
For example: suppose I set up Guide with my site, at 23:40 local time on 24 June 2000. When I click on the Moon, Guide will tell me that the Moon will rise at 00:04 local time on 25 June. Obviously, I'd want to know that the moon would be rising in 24 minutes. Had Guide followed the "usual" method, I would simply be told that the moon never rose on the calendar day 24 June.
Finally, under the method used by Guide, the rise/set/transit times do not vary according to the time zone. The moon's actual motion is not affected by time zones, of course, so it makes sense that the rise/set/transit times should not vary by time zone.
The scheme used by Guide will be absolutely essential when the rise/set/transit times are given for viewpoints on other planets. (Right now, Guide doesn't show that data yet.) From the Moon, a star rises and/or sets once every 27.3 days, so an event is unlikely to happen on a given calendar day. (And I'm not sure what a "lunar calendar day" would be anyway.)
When Guide starts up, the time it shows is off by one (or sometimes two) hours.
A: In most cases, this turns out to involve setting the correct time zone. Start up the time dialog in Guide, either by hitting Alt-T; selecting "Settings... Time Menu"; or clicking on the time shown in the legend. In the time dialog, select the Time Zone button (right under the "calendar" array of buttons). Then select the time zone you want to use.
In a few very unusual cases, people have still seen timing errors, even after doing this. I have never really figured out how such a thing could happen, but there is a workaround. Hit Alt-J; Guide will prompt you to "Enter test flag:" Type TOFFSET=1 if the error is one hour, or TOFFSET=2 if it is two hours, and click OK. Exit Guide, and start again.
In some cases, this will simply double the error, indicating that Guide made a correction, but going in the wrong direction. If that happens, repeat the process, but this time, use TOFFSET=-1 (or TOFFSET=-2). Again, exit Guide and restart.
I notice that when I ask for 'more info' on some stars, the error margins cited for distance, luminosity, and parallax are huge. Why?
This tends to happen for more distant stars. The actual error values for the parallax don't tend to vary as much, but if the parallax itself is small, you get huge uncertainties in the distance and luminosity.
For an example: suppose the parallax was measured as 100 +/- 5 milliarcseconds. That corresponds to an uncertainty of 5%, so the distance (in this case, 10 parsecs or about 32.6 light-years) is also known to within 5%, and the luminosity is known to about 10%. Not too bad, as these things go.
Now consider a more distant star, with a parallax of only 10 milliarcsec. The Tycho/Hipparcos measuring system doesn't get any better with distance, so we're still probably about +/- 5 milliarcsec. But this now means an uncertainty of about 50%, so the distance comes out as 100 +/- 50 parsecs, and the luminosity has a formal uncertainty value of about 100%. To make things worse, these more distant stars are generally going to be fainter, and will have more poorly-determined parallaxes.
In quite a few cases, you'll see that the error value for the parallax is greater than the actual parallax, something like "3 +/- 7 milliarcseconds". Or you'll see that the measured parallax is negative, say, "-4 +/ 3 milliarcseconds". This last happens because, if you measure a slew of stars with actual parallaxes of (say) 2 milliarcsec, but your measurements are good to three milliarcseconds, your "bell curve" of measurements will include some negative measurements. All this tells you is, "the star is very far away; so far that a meaningful parallax measurement could not be made."
If the parallax error exceeds the measured parallax, Guide decides that it can't determine realistic distance/luminosity data, and therefore doesn't show any.
Q: I've added some asteroids, and they're now showing up twice... why?
When you add asteroids, via either the "Edit Comet Data" function or the "Add MPC Comets/Asteroids" function, Guide is not very intelligent about realizing that the asteroid already exists in its own (built-in) element set. Therefore, you wind up seeing the object twice: once as shown with Guide's elements from the CD-ROM, a second time as seen from your own elements.
There are a couple of ways around this. The recommended one is to never add asteroid elements with these two functions. Instead, replace the entire set of asteroid data with the current version of the MPCORB database. Click here for details on using MPCORB in Guide. This page describes the advantages and drawbacks of MPCORB, and how to get the data.
When you use the MPCORB database, Guide doesn't show asteroids from its own built-in elements. (Logically enough, since all of them have been replaced with MPCORB versions.) So the doubling of asteroids does not occur.
You may have already used "Edit Comet Data" and/or the "Add MPC Comets/Asteroids" function. If so, those objects will indeed still be doubled, and you'll have to clean them out of the list of user-added asteroids before they become "single" again. There are two ways of doing this. You could click on "Extras... Edit Comet Data", and select the offending object. Click on it, then on "Delete", and it will be removed from the list (but will still appear, because it has not been deleted from MPCORB or from Guide's built-in elements). After that, it will only show up once.
This could be a little tedious, because you have to delete the objects one by one. Another solution is to edit the file COMETS.DAT with a text editor, and delete all the lines referring to asteroids. There is a number at the top that counts the number of valid lines in COMETS.DAT; be sure to reset this correctly (that is, if you delete 55 comets, subtract 55 from this number.)
The other way around the doubling problem is to make use of Guide's ability to 'filter' asteroids on the basis of various characteristics. If you hit Alt-J, you'll get a little dialog box asking you to "Enter a test flag:" You can then enter the text ASTFILTER=b, and Guide will suppress its built-in asteroids; only the objects you have added will be shown. Hit Alt-J again and enter ASTFILTER= (no 'b'), and Guide will revert to its "normal" operation and show the built-in asteroids.
Q: With Guide 8, how do I use the second CD-ROM?
A: By default, Guide does everything using the data from the first CD-ROM. You can install part or all of that CD-ROM with the "Extras... Install to Hard Drive" option. If you install everything from the first CD-ROM, then you can run Guide without the CD and still have all of Guide's features (but it will consume about 600 MBytes of hard drive space.) If you install only bits and pieces, then you'll find that some functions of Guide don't work unless the CD is in the drive.
Once you've done (at least) a "minimum install", you can run Guide with either CD-ROM in the drive, or with no CD-ROM in the drive. Guide will use whatever data it can access. If the second CD-ROM is in the drive, Guide will be able to show images of deep-sky objects from that disk, and the detailed bitmap of the Moon when you zoom in on it. You can also put the second disk in the drive, click on "Extras... Install to Hard Drive" again, and get a list of items that can be installed from the second disk.
There is some more discussion of this starting on page 55 of the users manual.
Q: I've got Guide 8.0, and my computer has two CD drives. Can I run Guide with a CD in each drive?
A: Yes. To do this, you will have to edit the file STARTUP.MAR and look for a line such as this:
18 drive d:\
...where 'd' will be the letter of the CD-ROM drive from which Guide was installed. If you had a second drive with, say, letter E:, you would change the above line to read:
18 drive d:\;e:\
After doing this, Guide will be quite flexible about reading data from both drives. You would need to have disk #1 in one of the two drives (doesn't matter which one). If the other drive had a non-Guide disk (or no disk) in it, Guide would simply ignore that disk. If the other drive had disk #2 in it, then Guide would make use of the data from it (for things such as showing the images of deep-sky objects and the detailed lunar image, for example.)
Q: Asteroids vanish for dates before 9 October 1995 12:00 UT, and dates after 9 May 2005 12:00 UT.
A: This happens in Guide 8. The best solution is to download and use the MPCORB asteroid data. Download the MPCORB dataset to your Guide folder, then use Extras... Use MPCORB, and Guide will switch to use of this dataset. In fact, I'd recommend doing this even if you are seeing asteroids with no difficulty, because MPCORB offers many advantages compared to the elements "burned into" the Guide 8 disks.
The asteroid data supplied on the Guide 8 CDs is becoming swiftly obsolete, because new objects are found and new observations are made of already-known objects. That was always true, even with previous versions of Guide. But new sky surveys are turning up lots of new data. The first round of Guide 8.0 disks had data for about 158,000 asteroids, of which under 32,000 had permanent numbers (that is to say, their orbits were considered "definite" enough that the objects could not be lost). The current MPCORB dataset has over 330,000 objects, of which over 160,000 are numbered!
The benefits are such that I expect that in Guide 9, MPCORB will be the default asteroid dataset. (A copy will be provided on the disks, but it will still be easy to replace this with a current copy of MPCORB.)
But in Guide 8.0, if you are not interested in higher-numbered objects, you can still get around the vanishing asteroids, without needing MPCORB. The elements for more distant eras were put onto the second disk. If Guide has access to that, the range over which asteroids are displayed runs from 6 Mar 1960 to 24 Feb 2023 (though over much of that range, only the 30,000-odd numbered asteroids are shown.) Also, of course, only asteroids known at the time the CD was made will be shown.
With the second disk in the CD-ROM drive, I'd recommend using Extras... Install to Hard Drive, and then clicking on "Extra Asteroid Ephemeris Range." This will ensure that all the elements needed to get asteroids to appear over the full range will be loaded to your hard drive.
I also had to do one other thing which will be a problem for some people. In Guide 7, elements near the current date were stored at 50-day intervals, so that at most, 25 days worth of perturbations were ignored. At distant dates, the element spacing switched to 200 days. In Guide 8, all elements are at a 200-day interval. That drastically reduced the storage requirements (which was necessary with five times as many objects.) But it does mean that up to 100 days worth of perturbations are sometimes ignored. (The solution to this will be to have Guide numerically integrate the orbits when ultra-high precision is required.)
Q: How do I get a shortcut (icon) for Guide on the desktop?
A: In theory, the 'setup' program should provide one for you. In practice, I've heard of several cases where that part of the install failed.
If that happens to you, right-click on the desktop, then on "New... Shortcut." If you installed Guide in the default directory (the one Setup suggests), then the command line should be "c:\guide8\guide.exe" (entered that way without quote marks). You can then select a name for the shortcut (probably "Guide"), click Finish, and you'll have the shortcut on the desktop.
Q: How do I get the updated Guide software I've downloaded to work?
A: First, make sure you've downloaded the update for the right version. There is a page to download the current Guide 8 software, as well as one for Guide 7 and one for Guide 6. For each, you can download one of three different versions, for DOS, Windows 3.1, and "32-bit Windows" (Win95/98/ME/NT/2000/XP).
The most common problem is with the .ZIP file not decompressing properly, or decompressing in the wrong directory. The files should be extracted in the directory in which Guide is installed. Some of the files extracted will replace existing ones, so you ought to get a message such as "Guide8.exe already exists. Do you want to replace this file, rename it, or skip it?"
The second most common problem is choosing "rename" or "skip". You really do want to replace the existing files with the new ones.
Finally, in some cases, people have done everything right and still thought that the update wasn't working. If you're running Guide 7 or later, the "Help... About Guide" option will give you a version date. With all versions, if you exercise the program very much, you'll see some nifty new feature(s) that were previously not there. (You may want to look though the list of new features, provided on the same page where you downloaded the update. Some of the new features will leap out at you, but others are more subtle, and none will be documented in your users manual; after all, they didn't exist when the manual was written.)
Q:How come I can get a certain asteroid to display at some dates, but not at other dates?
A: There are two problems at work here. Guide 8 stores asteroid data for the dates 10 Oct 1995 = JD 2450000.5 to 30 Jan 2005 = JD 2453400.5 on the first CD-ROM. If it has access only to data from that first disk, it will display asteroids properly between those two dates, and none outside of it.
Previous versions of Guide had a much larger coverage in time, but they also had about a quarter as many asteroids. The asteroid files are quite large; if I'd had to quadruple them, Guide 8 would have required a DVD (or maybe a third CD just for asteroid elements.)
But the second Guide 8 CD-ROM extends the time coverage in both directions. If Guide has this disk available, it can show all asteroids as far back as 27 Jun 1992 = JD 2448800.5 and as far ahead as 10 Apr 2007 = JD 2454200.5; and it can show numbered asteroids only (up to 30716, the highest-numbered asteroid when the disks were made in early 2002) over the time span 7 Mar 1960 = JD 2437000.5 to 25 Feb 2023 = JD 2460000.5.
So, you may ask, how does one evade these limits? I do have plans to support numerical integration within Guide, so that you can click on an asteroid/comet and tell Guide that you want to be able to track it over a user-defined time span. In the meantime, I have an option that makes use of the fact that Guide can display asteroids from the Minor Planet Center's MPCORB.DAT dataset. Download that file, and you can tell Guide to use it in place of its own "built-in" asteroid elements.
However, MPCORB.DAT gives elements at a "present-day" epoch. To use it for distant dates, you should use this program to integrate MPCORB.DAT to a desired epoch. By doing this, you can get all the elements you want, for any date you want. (The only drawback is that integrating all those objects back over decades or centuries can take a while!)
A: Guide doesn't install anything to the hard drive except in its own directory. Usually, unless you've overridden the default choice, this directory is c:\guide8. Delete this, and Guide will be uninstalled. (The program doesn't put anything into the Windows registry, nor any files/.DLLs in other directories. Doing so appears to be a recipe for disaster. I may eventually have to revise Guide to mess around with such things, but will avoid it if at all possible.)