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Northern Rockies Skies for November

October 27, 2011

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.

Say adios to the summer triangle of Vega, Deneb and Altair and welcome our beautiful winter constellations this month. The Milky Way rises up on the western horizon, going directly overhead and plunging down to the western horizon.

Overhead note two prominent constellations, Pegasus and Cassiopeia. Pegasus, the winged horse, is slightly to the south of the Milky Way and is recognized by its famous Great Square. The queen Cassiopeia easily is recognized by its stretched out "W" star pattern.

Rising prominently on the eastern horizon is Taurus the bull followed by Orion the hunter. Taurus, a majestic constellation, forms a prominent "V" in the sky and is the location of the nearest cluster of stars, the Hyades. Orion is a definite sign of the arrival of winter.

This month you will have an opportunity to view Jupiter, Mars and Saturn with the unaided eye. Right after sunset above the southeast horizon you will note Jupiter, which is the brightest object in the sky. Mars rises after midnight and Saturn, which is in Virgo, rises after 6 a.m. above the eastern horizon.

The Leonid meteor shower (about 40 meteors per hour) peaks Nov. 17 and is best seen toward the eastern horizon in the early morning after 2 a.m.

November 2011 Interest: Brown Dwarfs (best URL:

Astronomers had long suspected the existence of sub-stellar objects -- condensed spheres of gas-like stars, not sufficiently massive to fuse hydrogen into helium, but still considerably more massive than the gaseous Jovian planets of our solar system -- Jupiter, Saturn, Uranus and Neptune.

Calculations showed that such objects would need to have less than about 75 Jupiter masses (or 7 percent of a solar mass) to avoid igniting fusion in their cores. They would emit dim radiation, mostly in the infrared portion of the spectrum by virtue of the heat provided by continuing gravitational contraction.

The name for these objects was finally determined to be "brown dwarfs," as opposed to red dwarfs (true stars less massive than the sun). The first brown dwarfs were discovered in the mid-1990s; today approximately 1,000 brown dwarfs are known and studied.

While ordinary stars are supported internally against further gravitational collapse by the heat released in fusion processes, brown dwarfs lack this heat source and would condense to smaller sizes were it not for "electron degeneracy  pressure." According to the Pauli Exclusion Principle, no two electrons may share the same energy state (this principle is also fundamental to the periodic table of elements). So when gravity attempts to compress a brown dwarf, the electrons cannot be squeezed beyond a certain point. Their pressure thus pushes back, supporting the object against collapse.

This same principle is responsible for the internal pressure that supports ordinary objects on Earth against collapse, as first shown by the eminent physicist Freeman Dyson, also famous as a proponent of space travel.

Classification as a brown dwarf, rather than a red dwarf or a planet, requires tests. Since brown dwarfs do not fuse, primordial lithium created in the Big Bang is still present and detectable in their atmospheres by spectroscopic methods. Also, brown dwarfs may have planets. Kinematics of the mutual dwarf-planet orbits are used to determine the system's mass and thereby the main object's classification as a dwarf.

To view this month's sky chart, click here.

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