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.

Solar system objects

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.

Planets and satellites

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.)

Stars and galactic objects

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:

  • The Hipparcos/Tycho-2 catalogs. These provide high-quality position, proper motion, and parallax data. The complete datasets were released in June 1997, and represent a vast improvement over all previous catalogs. This is the main dataset used for the brightest 2.5 million stars.
  • the Yale Bright Star catalogue (contains large amounts of data for over 9,000 naked-eye or near-naked-eye stars, and is used to display Greek-letter and Flamsteed-number designations)
  • the SAO (Smithsonian Astrophysical Observatory) Catalog. With the arrival of the PPM, the SAO is now mostly of historical interest; the PPM provides more precise positional, proper motion, and spectral data. But there are still occasions where the SAO data is useful for comparison.
  • the PPM (Position and Proper Motion Catalog) and the PPM Supplement for stars down to about magnitude 11. For many purposes, the PPM has been replaced by Tycho. But there are still many cases where either a star is in the PPM but not in Tycho; or, where the proper motion given in the PPM is more precise than that given in the Tycho catalog. Since the PPM is based on observations in the 1950s, and Tycho/Hipparcos on observations made around 1991, the PPM tends to be more accurate for positions before about 1960 (though this varies from star to star). When you ask for "more info" on a star, Guide lists positions from each catalog, along with the formal error for those positions.
  • the HD (Henry Draper) and HDE (Henry Draper Extension) catalogs. For many of these stars, data from the Michigan HD catalog is also available; this provides extended spectral type data, such as luminosity classes.
  • the Hubble GSC (Guide Star Catalog) of over 15 million objects. This is often advertised as "extending to magnitude 15", which is true in some parts of the sky. In dense areas such as Sagittarius and Cygnus, this drops to about 13.5; the mag 15 claim is therefore somewhat misleading. But this catalog still provides precise positions and decent magnitude data for far more stars than any other catalog currently available, and forms the basis for almost all good star charting software these days.
  • 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.

  • the GCVS (General Catalog of Variable Stars) for over 37,000 known variable stars. This provides information about the type and period of variability, plus (often) additional spectral class data. Variables found since the GCVS was compiled, the so-called "Name List" stars, are also included, up to the most recent 76th Name List.
  • the NSV (New Suspected Variable) catalog, and the NSVS (New Suspected Variable Supplement) catalog.
  • the WDS (Washington Double Star) catalog, 2001 version. This provides data on the separation, magnitudes, and position angles for double stars.
  • the DM (Durchmusterung) catalogs. These four large catalogs were compiled back in the 19th century, and the data in them is (by modern standards) not very helpful. Still, stars are often designated using only their DM numbers, so this catalog is still quite useful for finding such stars.
  • Nebulae

    For nebulae, Guide draws on information from the following catalogs:

  • a catalog specially compiled by Eric-Sven Vesting, which removes many of the horrible cross-indexing problems attendant to all previous catalogs. Eric also put together nebula isophote data from RealSky data, leading to an unprecedented level of accuracy;
  • the Sharpless catalog of HII regions;
  • the LBN (Lynd's Bright Nebulae) and LDN (Lynd's Dark Nebulae) catalogs;
  • the van den Bergh catalog of reflection nebulae;
  • the Strasbourg catalog of planetary nebulae (1992), which includes the entire PK (Perek-Kohoutek) catalog, plus a few planetaries found after that catalog was assembled;
  • the Abell catalog of planetary nebulae.
  • Open clusters

    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.

    Globular clusters

    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.

  • the RC3 (Third Reference Catalog of Galaxies)
  • the UGC (Uppsala General Catalog)
  • the MCG (Merged Catalog of Galaxies)
  • the ESO/Uppsala (a southern-hemisphere extension to the UGC)
  • the NGC and IC catalogs (not generally very helpful, but these catalogs sometimes provide some descriptive data)
  • 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.

    Grids, reference marks, etc.

    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.