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Northern Rockies Skies for June

May 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.

The June skies always appear empty compared to the spectacular variety and diversity of the winter and spring skies. Don't fool yourself, though, the summer skies present a spectacular display of interesting objects.

With an unobstructed view of the northern horizon you see the notable constellations Cassiopeia and the Big Dipper overhead. Look for Leo the Lion nearby the Big Dipper. On the eastern horizon, you will see the bright star Vega rising first, then Deneb (more northerly) and Altair, which in combination make up the summer triangle.

Going toward the southern horizon you see the bright red star, Antare, in the constellation Scorpios. In a dark site you can see the Milky Way running almost parallel to the southeast horizon through these constellations.

There are numerous opportunities to view our planets this month. Saturn is in Virgo, near Spica, and can be watched from sunset until midnight. In the morning, you can see Jupiter, Mars and Venus just before sunrise.

June, 2011 Interest: Stars: III -- The sun's outer layers (best URL: )

A freight train traveling from Earth 100 miles per hour would reach our sun in 106 years -- one long human lifetime.

Meanwhile, light from the sun reaches us in only 500 seconds. The sun subtends close to 1/2 degree in the sky, only because it is so near. The nearest other stars -- roughly a million times more distant -- appear only as points of light in all but the largest Earth-bound telescopes. The sun's nearness affords us the opportunity for intensive study and provides a gateway to understanding all stars.

The photosphere is the sun's optically thick surface -- we cannot see deeper than this surface, which has a temperature of 5,800 degrees Kelvin and is responsible for the broad spectrum of the sun's visible light. When the sun is eclipsed by the moon -- blocking the extremely intense luminosity of the photosphere -- we can see the outer and inner atmospheres, the corona and the chromosphere, respectively.

The corona extends a few solar radii beyond the photosphere, pearly white in color with temperatures ranging in the neighborhood of two million degrees Fahrenheit. The energy that heats the tenuous coronal gas comes from magnetic "reconnection" processes in which anti-parallel magnetic field lines annihilate, producing kinetic energy and accelerating ions in the corona.

Extending only a few thousand kilometers above the photosphere -- a small fraction of the solar diameter of 1.4 million kilometers -- are many thousands of spicules, a dominant feature of the chromosphere. Spicules are small gas tubes, appearing as translucent fiery-red blades that materialize out of the photosphere and subside over several minutes.

Also erupting from the solar surface are long-lasting prominences -- much larger magnetic tubes carrying luminous gas -- arching up to a few hundred thousand kilometers over the sun. Sufficiently energetic prominences can break loose and speed through interplanetary space as part of the solar wind, colliding with the Earth's magnetosphere after a few days travel and energizing the aurora borealis -- the northern lights. Prominences erupt from regions on the photosphere populated with sunspots, our topic for next month.

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

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