Fall 1997

MegaStar Sky Atlas 3.0 for Windows

Arthur Babcock, MIRA Volunteer & Member, ASCC
(Please see "Looking Up" on page 5, for more on Arthur Babcock)
MegaStar Sky Atlas 3.0 for Windows
ELB Software
8910 Willow Meadow Dr.
Houston, TX 77031
713.541.9723
http://www.flash.net/~megastar

When MegaStar was first published in 1992, it was strictly high-end deep-sky observer's software: no planets, no animation, no images at all. Instead, the program displayed stars and nonstellar objects, and plenty of them. Shipped on forty 3.5" diskettes, the original MegaStar pioneered the use of the Hubble Guide Star Catalog (GSC) with its 15,000,000 stars as faint as magnitude 15.5, plus a database of 84,000 deep-sky objects.

MegaStar 3.0 builds upon this tradition while adding several new features. It is now much more of a "planetarium" program: one can display solar-system objects, including thousands of asteroids and periodic comets, and plot tracks of these bodies. Fields up to 180º wide can be displayed, with, optionally, constellation lines and boundaries. And provision is made for LX200 and Sky Commander interfaces.

At bottom, though, MegaStar excels as a deep-sky observing tool. The database numbers are even more impressive in the latest version: along with the GSC, one can use the Positions and Proper Motions (PPM) catalog of 330,000 stars, the General Catalog of Variable Stars (GCVS) and Suspected Catalogs of 28,000 variables, and the Washington catalog of 70,000 double stars. The Deep Sky Objects (DSO) database now includes 110,000 objects, including 93,187 galaxies. Fields as small as one arc-minute can be displayed, with or without user-configurable overlays representing the fields of view of eyepieces, finders and Telrad circles. An especially welcome feature of the original program was the plotting to scale of deep-sky objects, with galaxies rotated to show position angle (see illustration). Release 3.0 retains this feature, and also shows the actual contours of 225 bright nebulae.

  
An example of MegaStar's realistic rendering of galaxy shapes in the Virgo cluster (left), 
compared with a CCD image of the same cluster of galaxies.

MegaStar has the unwelcome distinction of being the only piece of astronomy software to play a significant role in a national news story. In November, 1996, a Texas amateur astronomer took a CCD exposure of comet Hale-Bopp, then on the inward leg of its epic journey past the Sun. Next to the comet on the image was an object with diffraction spikes that made it look to this gentleman something like the planet Saturn. When he consulted his MegaStar software to see what this body might be, he could find nothing in its position, and so that night on Art Bell's syndicated talk-radio show he announced a strange "Saturn-like object" that appeared to be "following" Hale-Bopp. In fact, as several people were quick to point out, the mysterious object was nothing more than an ordinary 9th-magnitude star, SAO 141894, but this explanation did not satisfy proponents of the SLO, as it came to be known. The debate raged on for weeks, primarily on the Internet, leading to denunciations of pseudoscience from one camp and imprecations against establishment cover-up conspiracies from the other (see "Hale-Bopp Funny Business" in Sky and Telescope, March, 1997, pp. 97-98). The whole affair would have been unrelieved low comedy if it were not for the tragic pall cast over it by the suicide of the Heaven's Gate cultists, who thought that Hale-Bopp was accompanied by a spaceship coming to collect them.

At one point in the debate it was suggested that this star was missing from MegaStar's database, but this is not true. The most likely explanation is that the Texas amateur had configured his software so that stars of SAO 141894's type were not displayed. It turns out that the Hubble Guide Star Catalog designates SAO 141894 as a "nonstar." In a sense, this is wrong, because SAO 141894 really is an ordinary star, but the GSC was made for the express purpose of aiming the Hubble Space Telescope, and "nonstar" is the catchall designation assigned to objects unsuitable as guide stars. These may be galaxies, asteroid trails or plate flaws, but the category includes as well a certain number of genuine stars whose images on the Sky Survey plates from which the GSC was made are unsuitable (too large, for instance) to serve for ultra-precise positioning. Now, MegaStar allows the user a great deal of flexibility in dealing with these "nonstars." One can display them in the normal manner, display them in a special color, or turn them off entirely. This last option, if used by the Texas amateur, would explain why his CCD camera showed an object where his software said there was none.

This explanation is no doubt a trifle involved and one may imagine that it would not hold up well in the atmosphere of talk radio. From it, however, we may derive the important observation that checking and rechecking with multiple sources is an essential step before one reaches a conclusion, and that a powerful research instrument such as the Hubble Guide Star Catalog or MegaStar Sky Atlas is no better than the uses to which it is put.

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