S Dor The S Dor type of variable star is a very luminous star that will irregularly (sometimes cyclically) erupt in brightness by one to seven magnitudes. They are usually the most luminous stars in their galaxy (S Doradus is the most luminous known star, about 500,000 times more so than the Sun). They are usually young, blue-hot stars surrounded by nebulae. SAx.0 SA1.0 SA2.0 The SA1.0, or "Selected A1.0" CD-ROM, contains about one-tenth of the stars listed in the A1.0 (about 50 million) and therefore fits on one CD-ROM. SA2.0 does much the same thing for the newer A2.0 catalog. In situations where their differences don't matter, both catalogs are referred to as SAx.0. Unlike the Ax.0 catalogs, SAx.0 is easy to get; and, like Ax.0, it can be viewed in Guide through the Get Ax.0 Data option. The only bad part is that the tenth of the stars selected are not the brightest 10%. SA1.0 is therefore mostly useless for star charts (and was never intended for that purpose anyway). It is a good dataset for astrometry, because the 10% selected have high-quality positions and guarantee an even density of stars over the entire sky. SAC The SAC (Saguaro Astronomy Club) database was compiled from a variety of sources, including the RNGC, NGC 2000, RC3, and many others. It incorporates corrections to most of these catalogs, and is generally a more reliable source than the RNGC and NGC 2000. Full documentation is in the \SAC directory of this CD-ROM. A partial list of those involved in the creation of this database includes: Bill Anderson Alan Gore Paul Maxson Steve Coe Steve Gottlieb John McGrath Dean Corn Mike Janes Tom McGrath Dr. Harold Corwin Jim Knott Brian Skiff A. J. Crayon Alister Ling Steve Stanford Bob Dahl Gene Lucas Dan Ward Paul Dickson Jim Lucyk Jeffrey Weintraub Jean Goddin Dr. Jack Marling Mike Willmoth SAO The SAO catalog is a list of 258,997 stars compiled by the Smithsonian Astronomical Observatory. It has most stars down to magnitude 8.5, plus a few dimmer stars. You can find a star's SAO number by clicking on it with the right mouse button. (Of course, it may not have one.) You can go to any SAO star by using the Go to SAO option in the Go to Star menu under the Go To menu. Saturn Saturn is best known for its bright system of rings. They are not solid, but made up of orbiting chunks of ice, either material that came from tides ripping a satellite apart or from a satellite that never formed. Inspection through a modest telescope shows some sub- divisions in the rings. The major one, the Cassini gap, separates the 'A' (outermost) ring from the 'B' (bright) ring. Just inside the B ring is the somewhat dimmer 'C' (crepe) ring. If you zoom in on Saturn in this program, down to about level 13, you will see these rings. You won't see the innermost 'D' (dusky) ring, which is very faint. Saturn takes 29.5 years to orbit the Sun; during that time, the angle at which we see the rings changes. At times, the rings are edge on to us, and you can't see them in a telescope. Inspection by the probes Voyager 1 and 2 showed a lot of finer structure. There are smaller subdivisions not noticeable from the Earth, 'spokes' that show radial brightenings and dimmings of the rings, and even some 'braided' rings. The dynamics of the rings are still not fully understood, and probably won't be until we send another probe out there to take a longer look. Saturn has eight major moons; the biggest, Titan, is the largest in the Solar System. Because it's big and is so far from the Sun (therefore cold), it holds on to an atmosphere denser than our own. Many have thought it a possible place for life to form. Saturn System I Saturn System II Saturn System III Measuring longitude values on Saturn is made difficult by the fact that the planet rotates more rapidly near the equator than it does at the poles. So three systems are used. Of the three, Guide currently reports only Saturn System I. Save a Mark } Let's say that you've set up a particular view that you like and want to save your location in the sky and everything about that view for later use. This is the function you use to do that. When you click on this option, you will be asked to provide a mark name. Enter this and hit Enter, and the position and display settings will be stored. When you want to go back to this mark, you can use the Go to Mark option. This item can be reached at any time via the } hotkey; or, you can reach it from within the File menu. Schmidt A Schmidt telescope (or "camera") is a specialized telescope for taking images of large areas of the sky. Most telescopes are not good for this purpose; their images become too blurry at the edge of a large field. Schmidt telescopes use a combination of a special lens of complex shape and a spherical mirror to avoid this problem. Scope Pad For many telescope systems, the Scope Pad menu option appears once you configure the telescope in the Scope Control dialog. Select that option, and a small floating dialog is shown. The top of the dialog contains arrow buttons and a central "stop" button, along with four radio buttons providing speed controls. This design was taken from the LX-200 keypad; for that telescope, all the buttons work. For most other systems (Sky Commander, Ultima 2000, etc.), the slew/speed/stop buttons do nothing. screen fonts printer fonts In Windows, you can change the fonts used, both on screen and in printouts, with the Screen Fonts and Printer Fonts options. Select one of these, and Guide will show a dialog box with the settings for the currently selected fonts. Change them and select OK, and that font will be used on all subsequent charts. screen size text zoom level 1-9 ALT-1...9 The third line of the legend shows your zoom level. This can range from 1 (seeing the maximum amount of sky, roughly an entire hemisphere) down to level 20 (seeing an incredibly small part of the sky). At Level 1, you see only those stars visible to an unaided eye; at each successive level, you see dimmer and dimmer stars up to about Level 10. At this point, the dimmest stars you see are of about magnitude 14 or 15. Also, this line shows how high the screen is at your present level. You can change your zoom level by using the Zoom In and Zoom Out options. You can also zoom in and out by hitting the * and / keys, no matter in which menu you are. You also can go to any particular zoom level from 1 to 9 by hitting the key corresponding to that digit. You can reach level 10 by hitting the 0 key, and levels 11 to 19 by hitting ALT-1 through ALT-9. Finally, you can set your zoom level by hitting ). This key brings up a control panel of twenty buttons, one for each level; hit a button, and you go to that level. Select Printer The Select Printer menu lets you tell Guide what kind of printer you have. The menu lists most popular printers; if your printer isn't listed, it's a good bet that it can at least emulate one that is on the list. Which one, and how you get it into that emulation mode, is probably described in your printer manual. You can also select "no printer" (the default), or you can "print", so to speak, to a .PCX file at any of three resolutions. If you select a printer capable of printing at more than one resolution, Guide will then list the different possible resolutions and allow you to choose one. select printer output In this menu, you select where you want printing output to go. If you select PRN or an LPT port, Guide will know to send data to that port and will ask no further questions. If you select a COM (serial) port, Guide will ask for the baud rate and parity. If you select disk file output, Guide will ask for the name of the disk file. You can copy the resulting file to the printer using copy (filename) prn /b This option is useful in two cases. First, suppose you want to make more than one copy of the printout. It may be faster to make a disk file, then copy it twice using the above command. Secondly, if the printer is on a machine other than the one Guide is running on, you can make the disk file, then copy it via floppy or other means to the machine with a printer. (Several users who run Guide at home but have access to better printers at work do this.) Select resolution This menu lets you select the resolution of printouts. Be aware that a higher resolution printout will look better, at the cost of taking longer. It may take some experimentation to decide what tradeoff is acceptable to you, and you may decide to change this from printout to printout. selenographic The term selenographic is the lunar equivalent of the term geographic. Just as there is a geographic system of latitude and longitude, there is a selenographic system of these coordinates used for maps of the moon. When you "click for more info" on the moon, Guide will show the current selenographic position of the Sun. This can be used, with a lunar atlas, to show what parts of the moon are near the terminator, and therefore, are in good positions to be observed. The position given is the point on the moon where the sun would be directly overhead; any point 90 degrees away from that point would be on the terminator. semidetached eclipsing binary In a semidetached eclipsing binary, the two stars are close enough that one is about at the point where tides from its companion star are about to rip some matter from it. Semimajor axis This line shows the semimajor axis, or mean distance from the Sun, of the asteroid. Most asteroids will be in the 2 to 5 AU range, putting them between Mars and Jupiter. Some will be closer in (and possibly cross the Earth's orbit); some are far from the Sun, like 5145 Pholus (20 AU, out around the distance of Uranus). Semiregular long-period Semiregular long-period stars are variable stars, giant or supergiant, whose variations in brightness are noticeably regular. Sometimes the regular changes are accompanied by or interrupted by irregularities. The periods run from 20 to more than 2000 days, and the changes run from a few hundredths to several magnitudes. This class can be subdivided into Z Aqr, RR CrB, Mu Cep, and SX Her types. separation When you look at a double star in a telescope or with an interferometer, you can measure how far apart the two stars seem to be, that is, their angular separation, measured in arcseconds. By itself, this doesn't tell you how far apart the stars really are. They could be close to Earth and therefore very close to each other, or they could be very far away and therefore not close to each other at all. If you can, by some other technique, find out how far the stars are from you, you can get the real, physical distance between them. SERC-J1 This plate in the GSC was taken using the U.K. SERC Schmidt telescope, using a singlet corrector, IIIaJ emulsion, and GG 395 filter. SERC-J2 This plate in the GSC was taken using the U.K. SERC Schmidt telescope, using a doublet corrector, IIIaJ emulsion, and GG 395 filter. SERC-V This plate in the GSC was taken using the U.K. SERC Schmidt telescope, using a doublet corrector, IIaD emulsion, and GG 495 filter. Set Location Location dialog The Location dialog, found under the Settings menu, provides a way to specify your "observing viewpoint". The very first line asks you to set your home planet. By default, Guide shows you the sky as seen from Earth; but you can select other planets and satellites from this list, allowing you to see, for example, the sky as seen from Mars. The next three lines ask you to set your latitude, longitude, and altitude. These do continue to have a meaning on other planets, by the way. For example, if you set latitude=longitude=0 on the moon, your viewpoint will be at the center of the side of the moon facing the earth; from this position, the earth will always be at the zenith. Next is a checkbox for "use geocentric position". Normally, your viewpoint will always be from the surface of a planet; but you can use this option to view from the center of a planet. (It was convenient to call this option "geocentric"; of course, if your home planet is the moon, then it is really "selenocentric", and so on.) Finally, there are options to reset the humidity, pressure, and temperature of your observing site. Right now, these are only used when on the earth, in a topocentric (non-geocentric) location. They are used to compute refraction and the visual magnitude limit given in Quick Info. Setting the animation rate In Windows, the animation rate is shown on a button in the Animation Dialog that is turned on in the Animation menu. In DOS, the animation rate is shown in the menu itself. In either case, you can reset the animation rate by clicking on it. When you do so, Guide will prompt you to enter a new animation step size. You can enter both a number and units; for example, "13 s" or "13 sec" will be read as "thirteen seconds per step"; "41 m" or "41 min" as "forty-one minutes per step"; "11 h" or "11 hr" as "eleven hours per step"; and "3 d" or "3 days" as "three days per step". Settings menu ALT-S The Settings menu provides the following controls: Set Location (lets you set your latitude, longitude, altitude above sea level, home planet, and other parameters) Colors menu (lets you set which colors are used to draw most objects and markings) (DOS only) Time dialog (lets you set Guide's time, time zone and calendar) Level size (lets you set the angular size used for the current zoom level) Scope control (lets you set up and communicate with an LX-200 or Sky Commander telescope control system) Language menu Margins menu RA/dec format (also lets you switch from English to metric units, set format used for latitude/longitude, and more) TLE=(filename) Projection menu Set Video mode (DOS only) Toolbar dialog (used to determine which buttons are shown on the toolbar) Sharpless Sh2- The Sharpless catalog of nebulae lists several hundred of the more important emission nebulae. Shift-F1 In the DOS version, you can use the Shift-F1 hotkey to reset the rotation of the chart. Hit this key, and you will be prompted to enter the rotation, in degrees (by default, this is zero). In both versions, one can instead reset the rotation in the Inversion dialog. shift-f2 By default, when Guide sends a command to an LX-200 or Sky Commander telescope control system, it will wait for 15 seconds for a reply. That's ample time for both systems. Some people with home-built telescopes emulating the LX-200 are using slower slew rates, and wanted a way to change that waiting time. When you hit the Shift-F2 hotkey, Guide will prompt you to enter the new delay, in seconds. SHIFT-F3 Add to Print Queue SHIFT-F4 Flush Print Queue The Add to Print Queue and Flush Print Queue options are used for batch printing. Batch printing allows you to set up a series ("queue") of charts to be printed, then to print them all at once ("flush the queue"). To do this, you set up each of the charts you want printed, with the chart settings exactly the way you want it for that printout. You set up the chart as desired, then hit "Add to Print Queue" to add it to the list to be printed. Each time you do this, Guide will tell you the number of printouts currently in the queue. When you're done and are ready to print the queue, hit "Flush Print Queue". Depending on what you're printing, it may take several minutes for Guide to flush all the printouts. You can add to the print queue from anywhere in the program with the SHIFT-F3 hotkey, and can flush the print queue from anywhere with the SHIFT-F4 hotkey. Shift-F5 This option leads to a menu showing all the overlays Guide knows about. Those currently set "on" are marked. You can toggle some overlays on or off, then return to the previous menu. You can reach this menu at any point with the @ hotkey. Short-period Beta Cep Short-period Beta Cep type variable stars are different because they have periods of usually less than a week and take almost equal amounts of time to climb in brightness as to decline. Otherwise, they are simply normal Beta Cep type objects. Show Eclipse This option, in the Extras menu, is slightly mislabeled. It also finds occultations and transits. But "Show Eclipse/Occultation/Transit" is a mouthful; the generic term "eclipse" will be used. The option provides a way to show the path on the earth cast by an eclipse or similar event. To use it, first set the date and time close to that of the event in question (no great precision is required) and select the objects involved in the event. For example, for a solar eclipse, you would right-click on the Sun and then click "OK"; then you would right-click on the Moon and then click "OK". (The order isn't important.) For a case where a star is occulted by an asteroid, you would right-click on those two objects instead. After you do this, the Show Eclipse option will no longer be grayed out. Click on it, and Guide will first determine that an eclipse exists (you'll get a "No eclipse found!" message otherwise). Guide will then clear the screen and show a world map with the eclipse path superimposed. You can then drag open boxes and zoom in and out, much as if it were a star chart instead of an "earth chart". When done, you can click on "Show Eclipse" again, to return to the "normal" star charting mode. The menus will be vastly different in eclipse mode; many things appropriate to star charts (constellation boundaries, for example) make little sense on earth charts. Shut off images The Shut off Images option provides a way to temporarily turn off the display of DSS images. side labels Side labels are labels on the edge of the screen showing intervals of right ascension and declination. Common on most star charts, this program lets you turn the display of side labels on or off and to adjust their spacing within the measurements dialog; or by right-clicking on a side label and then clicking "Display". The Margins menu has four check-boxes so you can decide which edges will get side labels when printing. sidereal mean solar day An object's sidereal rotation period refers to its rotation relative to the stars. For example: the moon's sidereal orbital period is about 27.3 days. This means that, if you were standing on the moon, you would see the stars rotate around you once every 27.3 days. Because the moon would, during those 27.3 days, move a bit around the Sun, you would see the Sun rotate around you about once every 29.5 days. This would be the mean solar day for the Moon. For similar reasons, those of us on the Earth see stars rotate around us once every 23 hours, 56 minutes, 4 seconds (the "sidereal day"), but see the Sun rotate around us once every 24 hours (the "mean solar day" for the Earth). Sidereal Time Local Sidereal Time Greenwich Sidereal Time LST GST Sidereal time, or "star time", is a time system used to express what portions of the sky are on the meridian. For example, if the Local Sidereal Time (LST) is 13:32:50, then objects on the meridian will have a right ascension of 13h32m50s. Thus, just as the "normal" time system used in everyday life closely matches the apparent motion of the sun, sidereal time matches the apparent motion of the stars. The two systems have almost, but not quite, the same rate of advance. The difference comes about because the sun appears to circle the earth once a day; the stars do so once every 23 hours, 56 minutes, 4.09 seconds, which is 3 minutes, 55.91 seconds less than a day. The result is that a sidereal clock put next to a solar clock would appear to run a little too fast. Just as there are different time zones used to describe where the sun appears from different parts of the world, one uses Greenwich Sidereal Time (GST) to describe what stars are visible from Greenwich, and Local Sidereal Time to describe what stars are visible from where you are.