Archive
04/07/11 – Ephemeris – The Ursa Major Association
April 7th. The sun will rise at 7:12. It’ll be up for 13 hours and 4 minutes, setting at 8:17. The moon, half way from new to first quarter, will set at 12:45 tomorrow morning.
The usual impression is to think that the stars of a constellation are actually located close together. This is usually not true. The stars of a constellation can be at vastly different distances. The Big Dipper is different. The five stars, excepting the two end stars of the dipper and 12 other dimmer stars in the general area are of similar distance and have the same motion through space. The group is called the Ursa Major Moving Cluster or Ursa Major Association, and is moving about 9 miles per second relative to us to the east and south. An association is a rather loose, sparse star cluster. This association lies about 75 light years away. If it were five times farther away, it would be the same distance as the Pleiades.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
03/29/11 – Ephemeris – Ursa Major
Tuesday, March 29th. The sun will rise at 7:29. It’ll be up for 12 hours and 36 minutes, setting at 8:05. The moon, 3 days past last quarter, will rise at 5:29 tomorrow morning.
The Big Dipper is now nearly overhead in the northeast at 10 p.m. The seven bright stars are second to Orion in the southwest as the seven brightest stars in a constellation. If you looked up a list of constellations, you’d find that the Big Dipper isn’t there. Ursa Major or the Great Bear is the constellation of which the Big Dipper is a part. The seven bright stars of the dipper is the rump and long tail of this constellation. The rest of the bear, including his head and legs are delineated by dimmer stars. An anatomical problem is its long tail, which was drawn in by the ancients of the old world. The American Indians, also saw a bear in the stars here, but the handle of the dipper became three hunters following the bear.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
My rather crude drawing of Ursa Major, the Great Bear
Bob Moler's Ephemeris Blog 