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Northern Rockies Skies for March

February 25, 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.

The Milky Way, the hazy band of unresolved stars that is our galaxy, stretches from the southern horizon to nearly overhead through the constellations Gemini and Auriga. It goes through Cassiopeia (the great "W" in the sky), and then plunges northward to the horizon.

You will see Capella, the She-Goat, nearly overhead. This yellowish star is about 45 light years away from the sun.

The March skies provide us with one of the most spectacular views of Orion, the prominent winter constellation that you probably have been watching most of these winter months. It sets about four hours after sunset.

Keep a constant eye on Jupiter, which is ever present in the western sky right after sunset. During the middle of March, get binoculars and focus in on Jupiter. You may see another fainter object to the north with it -- that will be Mercury.

Located in Virgo, Saturn rises after 9 p.m. and can be seen throughout most of the night. Venus is this month's bright "morning star."

March 2011 Interest: The Milky Way Galaxy IV -- Interplay of Components


In previous columns, we described the relatively recent comprehension of the nature of our galaxy, as well as its size and appearance, motions, timescales and some galactic components. Like any system made of parts, these components hold each other together by interactions -- forces of nature -- in a near dynamical balance. In a quasi-equilibrium state of the whole galactic system, momentum, angular momentum and energy are exchanged between several components.

Besides individual stars, gravitationally bound clusters of stars and enormous but tenuous gas clouds, three additional "less visible" components participate in governing the morphology of the visible parts. The most dominant is "dark matter," inferred to exist only by its gravitational influence. The other galactic components move in their orbits much more quickly than can be accounted for by their total mass.

Dark matter does not interact with luminous matter via the electromagnetic, strong or weak nuclear forces. Its total mass integrated over the universe is about five times that of ordinary matter. Like all other forms of matter, it is most likely particulate -- just another particle type yet to be discovered. The additional mass supplied by dark matter greatly influenced formation and evolution of galaxies, as the major fraction of "gravitational glue."

The two other invisible galactic components go hand in hand. They are quite familiar to us, and their interactions are well understood from terrestrial experience:  Cosmic rays and magnetic fields. Cosmic rays are fast-moving charged particles -- electrons and protons -- otherwise known as plasma.

Plasma is ejected and accelerated by stars (as our sun's solar wind) and by jets accelerated by super massive black holes at the centers of galaxies.

Moving charged particles create magnetic fields and the particles spiral around magnetic lines of force -- the two components are inextricably linked. The dynamics of galactic gas clouds, which contain plasma, are thus influenced by the pressure of magnetic fields. The whole system's circuit is completed by collapsing clouds that form new stars.

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

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