Wyoming Skies for October
by Ron Canterna, University of Wyoming
October 1, 2007
A monthly look at the night skies of Wyoming, written by Ron Canterna, professor in the University of Wyoming Department of Physics and Astronomy.
The summer triangle is still prominent in the western skies. This triangle of bright stars (Vega, Deneb, and Altair), connects the constellations of Lyra (the Lyre, Turtle or Vulture), Cygnus (the Swan), and Aquila (the Eagle).
Overhead, we find the great square of Pegasus (the Winged Horse) and Andromeda (the Chained Lady). Within the confines of the constellation is a unique viewing opportunity. The Great Andromeda Galaxy (M 31), the only naked-eye object that does not belong to the Milky Way galaxy, is the farthest object you will see without optical aid.
The Andromeda galaxy is two million light years away. If it could be seen in full extent is as large as three times the diameter of the full moon. In dark skies, look for it as a fuzzy patch just to the northeast of the Great Square.
Jupiter will remain bright in the west in the early evening. Mars rises around midnight and Venus and Saturn are near the bright star Regulus in Leo the Lion in the early morning sky. This is a great year to view the Orionids meteor shower, which peaks around Oct. 21. About 20 meteors per hour can be seen and are best viewed toward the east after midnight.
October Interest: The Harvest and Hunter's Moon
In late September and early October most farmers benefit from a phenomenon called the Harvest moon. The Harvest moon is a term used to describe the full moon that occurs nearest in time to the first fall day -- the autumnal equinox (Sept. 23).
Normally the moon will rise about 50 minutes earlier each successive day due to its orbit around the Earth. Sometimes when the orientation and position of the moon's orbit is just right, it will rise only 15 minutes earlier on successive days. This happens at and near the autumnal equinox.
Since the sun and the full moon are exactly 180 degrees opposite in direction, when the sun sets during the autumnal equinox period, the moon almost immediately rises on several successive days. This provides the Earth's landscape with full moon light throughout the entire night to the benefit of all harvesting farmers.
However, as most hunters realize, the full moon in October has similar properties (rising nearly the same time the sun sets) and it is useful to use this extended bright time to pursue their prey. The October full moon is called the Hunter's Moon and this year will occur Oct. 26. The Harvest moon was one month earlier.
You can get more details on the evening skies and a monthly star chart via the Wyoming Skies home page (http://wyoskies.uwyo.edu) or send an e-mail to firstname.lastname@example.org.