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of a number from 1 to 100, followed by a letter; for example, Hickson 42E would be the fifth galaxy found in cluster #42. The Arp catalog contains "peculiar" galaxies and groups of galaxies listed by Halton Arp. Many of these objects make for interesting observing with small telescopes. Their numbers run from 1 to 338. 5c: Finding nebulae When you click on the "Nebula" option in the "Go to" menu, you will get the following menu: Sharpless Lynd's Bright Neb PK (Strasbourg) Van den Bergh Barnard Dark Neb Common Name Abell Planetary To find an object by its Sharpless, Lynd's Bright Nebula, Abell, van den Bergh, or Barnard number, click on the option and type in the catalog number; Guide will recenter on that object. By the way, don't confuse the Abell catalog of planetary nebulae with the Abell catalog of clusters of galaxies (p. 11). The PK (Perek-Kohoutek), or Strasbourg catalog of nebulae, requires a pair of numbers. (These numbers actually form a coordinate for the object.) For this option, you enter both numbers, as in "249-5.1" or "215+11.1". The numbers will be separated by either a plus or minus sign. Most nebulae are known by their common names, such as the Eskimo nebula or the Trifid nebula. The "Common Name" menu provides a list of these names from which to choose. 5d: Entering coordinates Guide has provisions for entering coordinates in five different systems: equatorial (RA/dec), ecliptic, galactic, supergalactic, and alt/az. Entering coordinates is a fairly common task, so in Guide you can do it in several ways. If coordinates in any of these systems are shown in the Legend, you can just click on those coordinates and Guide will prompt you to enter new coordinates. For example, if the RA/dec is shown in the legend, you can click on it and Guide will ask for a new RA/dec. If the altitude/azimuth is shown, you can click on that and Guide will ask for an alt/az position, and so on for the other coordinate systems. Also, you can select any of these coordinate systems from the
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