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Friday, October 29, 2004
The lunar eclipse of night before last is plotted here against the stars:
The white section in the lower right-hand portion of the diagram is an inverted version of the near star field photograph from the eclipse set. The eclipse photograph is overlayed on a scan of map 10 of Wil Tirion's Sky Atlas 2000.0
The program, Sky (for the HP-48) calculated the position of the eclipse maximum to be lamda=73.7792, beta=0.06, which translates to western Aries at R.A. = 2h 10" 33.6' and decl. = +13.44°. The second contact, which is the moment represented by the star field photo occured 41 minutes before the eclipse max. As the moon advances on the 'fixed stars at a rate of 360° every 28 days, the 41 minutes of lunar advance add 1.46 minutes to the Right Ascention.
So, the penciled in circle is this new predicted location for the second contact. By comparing this to the photograph (the two reference stars have light gray circles around them) the moon was observed about three quarters of a degree the the west of the predicted location.
The major source for this error is most likely my failure to take the advance of the umbra into account. Also, I used Ephemeris 1950.0 numbers for the Sky program so that may be the source of some error.
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