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Northern Rockies Skies for October

September 29, 2010

A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis Idaho Observatory; and Daryl Macomb, Boise State University

The October night skies begin our introduction to the winter constellations, although the summer triangle is still prominent in the early evening. 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).

Around 9 p.m. we find the great square of Pegasus (the Winged Horse) and Andromeda (the Chained Lady) rising toward the zenith. Within the confines of Andromeda, the Great Andromeda Galaxy is the farthest object you will ever see without optical aid, although you may want a small telescope or binoculars to view it more easily.

The Andromeda galaxy lies two-million light years away and is as large as six 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 is seen just below the Great Square while Mars and Venus are waning in the early sunset skies. Watch for the Orionid meteor showers peaking around Oct. 21. Look to the east after midnight and expect to see 20 or more "shooting stars" every hour.

October 2010 Interest: Terrestrial Gravitational Wave Detectors

Last month we discussed gravitational waves, believed to originate from orbital motions of very dense objects -- like pairs of black holes or neutron stars. Upon arrival at Earth these waves induce incredibly minute strains, approximately one thousandth of a proton's diameter over one kilometer!

Such small strains may be detectable only because the sources, due to their orbital motions, make periodic waves. Earth-based detectors would see vibrating strains, like a miniature tuning fork. Gravitational wave observations will be important because they are unaffected by obscurations -- dust or electron plasma -- that prevent us from observing some celestial phenomena with light.

The terrestrial state-of-the-art project for detecting gravitational waves is the Laser Interferometer Gravitational-Wave Observatory. LIGO comprises two facilities, one in Louisiana, the other on Washington State's Hanford Nuclear Reservation. Simultaneous detection of identical signals by both experiments would constitute good support for a celestial origin of the signal -- not arising from trucks rumbling down the highway.

The LIGO experiments consist of pairs of four-kilometer tubes with laser beams bouncing off high-precision mirrors at the tube ends. The four-kilometer length separating the mirrors varies ever so slightly with passage of a gravitational wave. This variation is detected using techniques that record phase shifts in the laser beam light. Much effort is invested in noise reduction and vibration isolation to eliminate Earth-based effects that could mimic the gravitational signal.

The frequency range for gravitational waves from pairs of orbiting black holes and neutron stars is from a fraction of 1 Hz to roughly 1000 Hz. The binary black holes and neutron stars may be detectable with planned upgrades to the LIGO detectors (projected date, 2014) out to distances of about 25 million light years.


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