Northern Rockies Skies for September

August 31, 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

Directly overhead after dusk the summer triangle (Vega, Deneb and Altair) will dominate the early September sky.

The constellation Scorpius lies on the southwest horizon with its brilliant red star Antares. Overhead the Northern Cross or Cygnus, "the swan," is embedded in the summer triangle.

This is again a great opportunity to view the plane of our Milky Way galaxy that stretches from the southwestern horizon, arching up directly overhead, and plunging eastward on the northern horizon. The remaining constellations that "connect" the plane of our galaxy are Cepheus, Cassiopeia (the great "W" in the sky) and Perseus, located on the northeast horizon.

The two most prominent constellations to follow on the eastern horizon are Andromeda, "the princess," and Pegasus, "the winged horse." Pegasus can easily be spotted since its body is dominated by the famous Great Square of four stars.

Venus remains the evening star but is slowly ending its mission. Jupiter rises in the east after sunset and will be your ever-present guide to the stars during these crisp September nights. The first day of fall is Sept. 23 this year, and a full moon will usher it in.

September 2010 Northern Rockies Skies Interest: Gravitational Waves

Nearly all the information that we have detected from celestial objects is via the electromagnetic "channel": Radio waves, microwaves, infrared, visible light, ultraviolet, X rays and gamma rays. Another channel, for which signals have yet to be directly detected, is gravitational waves, or gravitational radiation.

Like the particles of electromagnetic radiation, called photons, gravitational radiation is hypothesized to consist of gravitons, also traveling at the speed of light. The graviton communicates the ordinary force of gravity between two objects, for instance, the sun and the Earth.

If the sun were to shake back and forth, the resulting gravitational disturbance at Earth would feel like gravitational waves, pushing and pulling the Earth. Gravitational waves are envisioned-- following Einstein's formulation -- as "ripples in space-time," analogous to waves produced on a water surface when disturbed by a passing boat.

In real life, binary stellar systems consisting of two neutron stars are expected to produce gravitational waves. Being very dense objects, the neutron stars make very strong waves. However, upon traveling thousands of light years to reach Earth, the waves are extremely reduced in strength. The gravitational disturbance, or strain, experienced by a detector on Earth may then be about one part in 100 billion billion -- equivalent to one ten-thousandth of a nanometer over a length of ten thousand kilometers -- seemingly impossible to measure.

Indirect evidence for gravitational waves came from measuring the decreasing orbital period of the famous Hulse-Taylor binary pulsar.

Next month we will discuss ground-based and space-based experiments designed to verify directly the existence of gravitational waves.

See for more information.

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