Objects shown and catalogs used in Guide
The objects shown in Guide can be roughly divided into solar system objects , objects inside our galaxy (stars, nebulae, clusters, etc.), objects outside our galaxy (other galaxies and clusters of galaxies), and "unobservable" objects (coordinate grids, constellation borders, Telrad sights, etc.)
In addition to these, there are about a hundred catalogs that users have added to Guide over the years, now provided right on the Guide 8.0 CDs.
Most people using Guide do so in order to create charts, so a lot of control is provided over how objects are shown: their limiting magnitudes, colors, and so forth. By default, Guide makes some "reasonable" assumptions in such matters by, for example, showing stars to about magnitude 14 for a one-degree field of view and to magnitude 4 for a 180-degree field of view. But if you want to override its judgments, this is quite straightforward.
Inside the Solar System, Guide shows planets and satellites, asteroids, and comets.
For all solar system objects, one can easily generate an ephemeris and/or a "trail" on the chart showing the object's motion. One need only click on the object with the mouse, and specify the number of positions desired and the time interval between those positions. The user interface makes this a very simple, straightforward task. Here's a screen shot showing the paths of two comets.
Data such as position (apparent and mean coordinates in any epoch), magnitude, distance from Sun and Earth, angular size, elongation, rise/set/transit times, and some orbital data is displayed for all solar system objects.
Guide shows the Sun, all nine planets, the Earth's moon, and all natural satellites except five "oddball" ones of Saturn (two co-orbital "ring shepherd" moons, and three tiny rocks that are at Trojan points of larger satellites... none apt to be observed with anything short of the Hubble Space Telescope.) The positional accuracy of the planets and Earth's moon is better than one arcsecond for dates between 1900 and 2100. As one goes outside that range, the accuracy slowly worsens to the order of (roughly) several arcseconds for dates several millennia ago or in the future. Turn on Guide's "high-precision" feature, and the accuracy becomes much better, down to the milliarcsecond level for dates near the present. A full discussion of planetary precision is available.
For some objects, special information is provided; for example, for the moon, times of phases, perigee, apogee, and eclipses are given, as well as libration information and data about the subsolar point; for Jupiter, times of satellite events are given; for the Sun, twilight times and times for equinoxes and solstices are shown. The rings of Saturn are displayed, and all objects are shown with proper phases and position angles. One can also specify that the solar system be viewed from any planet or satellite; the view from some of the outer moons of Saturn, for example, can be especially interesting.
Guide uses the Lowell asteroid database as the basis for asteroid information. This database contains data for over 150,000 asteroids, though some were never very well observed and are now lost. Over 30,000 of these objects are numbered.
Guide provides exceptionally precise positions for asteroids. It does this by storing orbital data for 200-day intervals; this means that most of the effects of planetary perturbations are accounted for, meaning that positions are usually accurate to about an arcsecond. It provides data on the orbit, size, discovery, name, provisional designation, and albedo for most asteroids.
Over the last few years, the number of known asteroids has exploded, and is continuing to explode. So Guide's built-in database is gradually becoming obsolete. You can avoid this by downloading the current MPCORB database from the Minor Planet Center. This is continuously updated and will ensure that you have the latest data for asteroids.
Guide contains data for all known historical comets, and it is easy to update its database to include newly discovered comets using orbital elements published in astronomy magazines or by the Minor Planet Center. One can easily specify that comets down to a given magnitude limit are to be displayed; they are shown with tails of correct orientation and approximately correct length. (Some guesswork is necessary for lengths, since tail lengths are not really predictable. Guide's formula for this is quite good, though; click here for details.)
Within our galaxy but outside the solar system, Guide displays stars, nebulae, open clusters, and globular clusters. The non-stellar objects are often cross-indexed to (and displayed using) NGC or IC information.
Guide draws on a variety of databases for star display:
Guide has the (admittedly rather slight) advantage of use of the GSC-ACT version of this catalog, instead of the original GSC-1.1 catalog.
For nebulae, Guide draws on information from the following catalogs:
Guide shows over 1,200 open clusters from the Lund catalog. This catalog is a compilation of clusters from the NGC, IC, Collinder, Berkeley, Melotte, and dozens of other sources, and shows information about the positions, sizes, magnitudes, and (in some cases) ages of these objects.
Guide displays all known globular clusters in this galaxy, with complete data for magnitude, position, and angular diameter.
Galaxies and clusters of galaxies
Guide displays galaxies using the PGC (Principal Galaxy Catalog). The current version of this catalog contains over 190,000 galaxies, and is cross-referenced to all the catalogs listed below. In itself, the PGC contains an impressive amount of data concerning the appearance, redshift, and designations for galaxies. When you click with the mouse on a galaxy shown in Guide, information will be shown from the PGC and some, and possibly all, of the galaxy catalogs listed below.
In addition, Guide can display data using the LEDA "Million Galaxy" catalog. While this provides more than five times as many galaxies as the PGC, the quality and amount of data is not nearly as good. For most objects, all LEDA provides is the position and magnitude of the galaxy, along with its size and orientation. In some cases, a cross-reference to an earlier catalog is given. For most uses, the 190,000 galaxies provided by PGC will be overkill anyway.
Guide also shows the full Abell and Zwicky catalogs of clusters of galaxies. Some basic information such as magnitudes and estimated sizes and distances are also provided for these objects.
Guide shows coordinate grids and tick marks, the horizon, ecliptic, galactic equator, an "eyepiece circle" of any desired angular size, a rectangle that can be resized and positioned to match a given CCD or film image, a Telrad sight, and constellation borders, lines and labels. Extensive control is provided for all of these, enabling one to turn them on, off, change colors, grid intervals, or set the field sizes at which such objects are shown.
Here's a screen shot showing many of the markings provided in Guide. In this case, a "user horizon" is turned on, showing some trees, cars, houses, etc. to convey a sense of where one is looking; constellation borders are shown, along with the "stick figures" commonly used to connect bright stars in a constellation.
