View finders. Most telescopes are equipped with some sort of view finder which has been collimated to the larger telescope. Where the view finder points, so points the telescope. One form may be a zero-power finder typified by the "Telrad" design which projects an illuminated reticule "bullseye" pattern against the sky. Where ever the bullseye is pointed, the telescope is also pointed there, allowing for quick acquisition of bright stars and deep sky objects. The other typical viewfinder is a finder scope. Very simply, a finder scope is a small, low power, wide field telescope used to aim a larger telescope at a remote object. As a general rule, most astronomers find it much easier to point a telescope using some form of aide because telescopes typically have very restricted fields of view, even when using a wide-field eyepiece. Without the use of some form of pointing device, astronomers may spend an entire evening gazing through a very capable instrument, but without ever seeing anything of interest.

Very often, the typical finder scope will be a small 6X30 (6X = 6 power = magnifies 6 times, with a 30mm objective) which most amateurs find to be too small to be of much use. Mind you, this is not to say that the 6X30 finder scope is without its uses. I use mine as a paper weight! Indeed, experienced deep sky observers will generally mount the largest possible finders on their telescopes, sometimes several, often with objectives up to and larger than 100mm (4 inches) in order to use fainter stars as an aide to tracking down more difficult deep sky objects [6]. As a general rule, when star-hopping, I'll often use both a Telrad and finder scope to take advantage of the strengths of both view finders. In this way I can quickly orient on a prominent field star close to the deep sky object of interest with the Telrad, and then switch to the finder scope to help finally zeroing in on my quarry. Stumped as to what size to consider? Nothing less than a 8X50 finder scope should be considered. They are cheap and readily available.

A final word about finder scopes, and by association telescopes and the orientation of their fields of view. You need to take the time to determine both the field of view of your finder scope and that of your telescope's eyepieces. Knowing the size of your field of view will allow you to know how much of the sky you can see with what ever combination of finder scope, telescope and eyepiece you may choose [7]. In star hopping, one typically starts with a finder scope with the wider field of view, finds the correct location, and then zeros in on the selected object with a lower powered (but typically wider field of view) eyepiece before going to higher powers for observation. A key point to note is the orientation of the field of view in your finder scope and telescope eyepieces. Very often they are different and may lead to difficulty in switching between the finder scope and the telescope. Most telescopes (remember that the finder scope is a small telescope, the Telrad not being a telescope is not a problem here) change the orientation of the image as it is magnified and passed through the eyepiece. Generally, refractors and catadioptric telescopes (Schmidt-Cassegrains) used with standard star diagonals produce mirror reversed images. Newtonian telescopes typically present inverted images. This is an important fact to remember, and when forgotten or poorly understood, has been the cause of much frustration among even experienced observers [8].

Star Charts. In amateur astronomy, much like driving a car cross-country, you are only as good as your road maps. The better the map, the better the job you'll be able to do when you try to locate your destination. Instead of mapping out terrestrial roads, star charts map out the heavens in greater or lesser detail. In a sense, you might also say there is a hierarchy of star charts. At the lower level of resolution, star charts might map out the constellations and bright stars, and often the Messier objects such as found in "Planning A Messier Marathon" [9] or in several of the popular astronomy magazines such as Astronomy or Sky and Telescope [1, 2]. In greater detail, thus offering a greater selection of deep sky objects and stars to 6^th magnitude as well, is Wil Tirion's "Bright Star Atlas 2000.0 [10]. Stepping up to Wil Tirion's Sky Atlas 2000.0, represents a significant jump in detail with 43,000 stars to 8^th magnitude plotted along with 2,500 non-stellar objects on 26 charts [11]. Sky Atlas 2000.0 is often the first "serious" star atlas an amateur moves into when they decide its time to really start chasing down objects beyond the "big and bright" or Messier objects. However, experienced amateurs often quickly find themselves exceeding the limits of Sky Atlas 2000.0 and needing to go farther. The next step, and arguably the current standard, is Uranometria 2000.0, which in its two volumes, charts some 300,000 odd stars to magnitude 9.5 as well as 10,300 non-stellar objects[12]. Recently, the three volume "Millenium Star Atlas" has been published with more than a million stars to 11^th magnitude and about the same number of non-stellar objects as Uranometria [13]. However, at $249 for the set, a price which begins to approach that of a used 486 note-book computer, many advanced amateurs have opted instead to use one of the now popular computer sky atlases.

Computer Star Charts. Once the province of only the well heeled or drop dead serious professional astronomer working in UNIX, computer based star atlases have in many ways eclipsed the capabilities of a traditional, paper bound star atlas, in that they can be customized to meet the needs of the user. Need a customized finder chart specifically set up for your telescope and unique selection of eyepieces? Computer based star charts can offer a chart reflecting the "zoomed in" field of view of your favorite eyepiece for those instances wherein you are trying to identify the individual members of galaxy groups and clusters. Popular computer star atlas programs include "Megastar"[14], "The Sky"[15], "Pluto Guide"[16], "Earth Centered Universe"[17], and others.

Putting it all together: Star-hopping to Pal 13

Buried beneath the "Great Square of Pegasus" is one of a series of globular clusters previously unknown until discovered by chance on photographic plates taken as a part of a National Geographic sponsored sky survey in the 1950's, the Palomar Sky Survey (POSS) [19]. Dubbed the Palomar (Pal) globular clusters, these 15 globular clusters represent some of the largest (³ 220 parsec diameter) and most distant (between 93 and 130 kiloparsecs) globular clusters in the galaxy [18, 20]. Taken all together, they represent an observing challenge for even the most accomplished observer.

Pal 13 is conveniently located for star-hopping near Alpha (a ) Pegasi, the star marking the southeastern corner of the "Great Square of Pegasus." However, Pal 13 may prove to be a difficult target. It is very small, only .7 arc minutes in apparent diameter. More importantly, it is relatively dim. With a 13.8 total visual magnitude, its brightest stars are less than 17^th magnitude [21, 22], suggesting that even under the darkest skies it will be a difficult target and will require high power. It is here that we begin our star hop.

A quick check of Sky Atlas 2000.0 reveals that Pal 13 is not plotted. You'd have to plot its location by hand if you wanted to use Sky Atlas 2000.0. Uranometria 2000.0 is my preferred star atlas when I’m not using Megastar to prepare finder charts. Turning to the back pages of Uranometria, 2000.0, Volume 1, The Northern Hemisphere, presents an azimuthal equal area projection of the constellations superimposed over a grid representing the Uranometria's 259 charts in Volume 1, where we find that Alpha Pegasi is located on chart 213 (Figure 1). Turning to chart 213, we find that Pal 13 is located below and slightly to the left of Alpha Pegasi (Figure 2). Here, I have superimposed an approximate 1 degree field of view, which when centered on Alpha Pegasi, just touches the star SAO 108393. By sweeping 2 more fields of view to the south, Pal 13 will appear in the field of view. Be sure to check the field stars (Figure 3), as a small galaxy, NGC 7479 is located about 1/2 degree to the southwest of Pal 13. However, at 4 X 1 arc minutes in size, it should be easily distinguishable. Additionally, an even smaller galaxy, NGC 7495, is located a little less than a degree to the southeast. Be careful in this case. NGC 7495 is about the same size as Pal 13 and about the same magnitude, so check your field stars to confirm your observation.