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The Sky This Week, 2010 September 7 - 14

A weekend trip to Andromeda
Waiting for Andromeda
Savage Farm, near Bluemont, VA
September 2005

The Moon spends the last two weeks of astronomical summer waxing in the evening sky.  New Moon occurs on the 8th at 6:30 am Eastern Daylight Time.  This is an important date in two of the world’s major religions.  For Jews it marks Rosh Hashanah, the traditional beginning of the new year.  For Muslims, the sighting of the first crescent Moon on the following evening marks the end of the fast of Ramadan and the celebration of Eid ul-Fitr.  Luna’s crescent waxes as she passes the planetary duo of Mars and Venus during twilight on the 10th and 11th.  On the evening of the 13th she will be just west of the ruddy star Antares in the constellation of Scorpius.  She ends the week crossing the dense heart of the Milky Way among the stars of Sagittarius.

I had the rare treat this past holiday weekend to not only benefit from the season’s first spate of wonderfully clear weather, but also an unfettered calendar for the evenings.  I took the opportunity to head off to a relatively dark site in Virginia’s northern Blue Ridge Mountains with my trusty 14.5-inch telescope to take in views of some summertime and rising autumnal favorite “deep sky” objects as well as the thrill of the chase in hunting down more distant celestial quarry.  For several hours I had an open meadow to myself, the crickets, katydids, and the stars and alternated between staring through the eyepiece at some far-off smudge of intergalactic light and kicking back in my observing chair and taking in the sight of the arching Milky Way with my slightly-corrected normal vision.  Such nights are as close to perfect as skywatching can get.  Moderate temperatures and transparent skies highlight the change of the seasons from the brighter star patterns and dense starfields of the summer to the relatively sparse constellations of fall.  On several occasions I pointed the big telescope at a random knot of naked-eye brightness in the Milky Way to be rewarded with an eyepiece full of a riot of distant stars too numerous to count.  However, the evening’s highlight came just before packing up the car for the drive back to civilization.  In the wee hours, high in the eastern sky, you’ll find a square-shaped asterism of second magnitude stars, part of the constellation of Pegasus.  Diverging from the northeastern corner of the square are two “chains” of stars, the lower one brighter than the upper, marking the constellation Andromeda.  Just north of the two stars that form the second ‘links” in the chains is an object that looks like a small detached part of the Milky Way, although the plane of the galaxy itself is several degrees distant.  This is the famous “Great Nebula” in Andromeda, first noted by the Persian astronomer al-Sufi in the 10th Century, and now known to be our closest intergalactic neighbor in space.  Some 400 billion stars comprise the Andromeda galaxy, and I spent about 20 minutes in rapt attention as I scanned the glow of those distant suns.  Simon Marius, the astronomer generally believed to be the first to view the object through a telescope around the year 1612, described the nature of its light as “that of a candle shining through [a ram’s] horn”.  I can think of no better description myself.  The light is airy and diffuse, stubbornly refusing to resolve into any kind of point source.  Subtle shadings and mottlings betray the presence of star clouds and dark rifts similar to those we see in our home galaxy, and the intensity of the light builds to a nearly stellar spot in the galaxy’s center.  Two satellite galaxies, both of which would be showpiece objects if they were isolated in the sky, accompany the great galaxy as it marches across the vault of night.  While the Andromeda galaxy is a wonderful treat for binoculars and small telescopes, it is simply magnificent in a large instrument at a dark site.

From the distant reaches of deep space to the more familiar confines of our solar system, the early evening twilight sky still offers views of the Earth’s two closest planetary companions as they race each other ahead of the advancing Sun.  Venus and Mars are now forging eastward away from the bright star Spica, which they both passed in the last two weeks.  This week the two worlds are briefly joined by the slender crescent Moon.  On the evening of the 10th Luna lies just south of Spica, with Mars and Venus to the left.  On the 11th she is east of Venus, with Mars just above and to the left of Spica.  This will be the last good opportunity to see the Moon and Venus together in the evening sky this year.

Giant Jupiter is inching closer to opposition on September 21st.  He now rises at around 8:00 pm, and his bright glow will command your attention shortly afterward.  Jupiter is about as bright as he can get since he is close to the perihelion point in his 12-year orbit around the Sun.  This also means that his disc is about as large as can be seen from Earth, almost 50 arcseconds across.  If you own a small or modest telescope, this will be the best year to seek fine detail on his surface markings since 1951!


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