|MadSci Network: Astronomy|
For a couple minutes, I thought you were asking something too obscure for my limited resources! It turns out this star isn't as obscure as I was afraid of. I found what you want in the 1998 Nautical Almanac, commercial edition, published jointly by Paradise Cay Publication and Celestaire, Inc. Alnilam is magnitude 1.8. In December, 1998, it was located at SHA 275 degrees, 57.4 minutes, that number decreasing by roughly .2 minutes per month. Its declination is South 1 degree, 12.3 minutes, almost constant. This works out to a Right Ascension of 5 hours, 36 minutes, 10.4 seconds in December 1998. Alnitak is magnitude 1.9. In December, 1998, it was located at SHA 274 degrees, 49.2 minutes, that number decreasing by roughly .2 minutes per month. Its declination is South 1 degree, 56.7 minutes, almost constant. This works out to a Right Ascension of 5 hours, 40 minutes, 43.2 seconds in December 1998. Right Ascension (RA) is the time between when the "First Point of Aries" (a confusing historical misnomer - LONG ago, it USED to be in the constellation Aries) reaches its highest position in the sky, and the time when the object of interest reaches its highest position in the sky. Sidereal Hour Angle (SHA), which Celestial Navigators use, is just backwards of Right Ascension. RA is measured in time, SHA is measured in degrees. SHA is the angle (positive westwards) between the "First Point of Aries" and the object of interest. RA (in DECIMAL hours)= (360-SHA(in DECIMAL degrees)) / (15 degrees/hour) [Moderator's note: the change in SHA that David refers to is due to precession. I mention this because, while celestial navigators use the current equinox, astronomers use a standard equinox (J2000) for celestial coordinates. If you don't know what I'm talking about, you can find out more about celestial coordinates in almost any astronomy book, and don't worry- his coordinates should be accurate enough for your purposes.]
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