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The Sky This Week, 2013 November 12 - 19

The Moon and the Seven Sisters
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 Messier 45, the Pleiades star cluster
Imaged 2012 January 25


The Moon brightens the lengthening nights this week, passing from the dimmer constellations of autumn into the rising stars of the Great Winter Circle. Full Moon occurs on the 17th at 10:16 am Eastern Standard Time. November’s Full Moon is commonly known as the Frosty Moon or Beaver Moon. In the latter case the name can be traced to the activity of these industrious rodents, which are working hard to gather food and fix their dens for the upcoming winter. Luna’s full disc may be seen about six degrees south of the Pleiades star cluster on the night of the 17th. On the following night she will be just four degrees east of the bright star Aldebaran in the constellation of Taurus, the Bull.

As the Moon waxes toward the full phase the terminator slowly sweeps across the vast lava plain known as Oceanus Procellarum, the Ocean of Storms. This huge lunar "sea" is the confluence of several lava flows that resulted from the impacts of large asteroids about 3.5 to 4 billion years ago. Its surface is relatively smooth but punctuated with the scars of more recent impacts, the most recent of which created the distinctive craters Copernicus and Aristarchus a few hundred million years ago. As dazzlingly bright as the Moon appears through the telescope, it is worth noting that some of the darkest samples of lunar soil were returned from this region by the crew of Apollo 12, which departed for the Moon on November 14, 1969. These samples had the reflectivity of a charcoal briquette!

Look a few degrees above the Full Moon on the night of the 17th. You should be able to see the small compact group of stars known as the Pleiades despite the lunar glare. This small asterism is one of the most storied groups of stars in the entire sky, probably second to Orion in terms of skylore from the many cultures that have risen and fallen throughout human history. That they have played a major role in some of these cultures is backed up by the fact that a number of ancient ruins such as the Parthenon in Greece and the pre-Columbian temple complex of Teotihuacan in central Mexico have their main axes aligned to the cluster’s rising point on the local horizon. They form a true star cluster dominated by several hot blue stars of relatively recent age located some 400 light-years away from the Earth. Most of us can perceive six of seven stars with the naked eye, while exceptionally keen eyed people can see up to 14 from a good dark-sky location. Through a telescope dozens of fainter cluster members can be seen, and the total number of stars associated with the cluster may be up to 1000.

The early evening sky is now dominated by the brilliant glow of Venus, which may be easily spotted in the southwestern sky as dusk falls. She is steadily moving eastward against the background stars, and this week she passes through the easternmost stars of the constellation of Sagittarius. She is also beginning to gradually move northward along the ecliptic, which will allow her to become a bit more prominent over the next several weeks.

Jupiter replaces Venus as the brightest star-like object in the sky, rising about an hour after Venus sets. He is preceded by the bright stars of the Great Winter Circle led by the striding figure of Orion. His bright golden hue contrasts nicely with the colors of the Circle’s brightest stars. Through the telescope Jupiter is the most satisfying solar system object to observe after the Moon. His disc is striped by dark parallel cloud belts and his rapid rotation changes the view over the course of an evening’s views. In addition to the planet itself, there are four bright moons that weave their way around their giant master, changing their configuration from night to night. A particularly good night to check Jupiter out will fall on the 14th; at 11:00 pm EST you can see the Great Red Spot, the shadow of the largest moon Ganymede, and the dark disc of the moon Callisto in transit across the giant planet’s face. As the night passes you can see Callisto exit the disc followed by Ganymede’s shadow. Ganymede itself begins to transit the planet at about 1:40 am if you’re planning to stay up late!

Ruddy Mars is best seen before dawn south of the stars of the constellation Leo. His distinctive red tint contrasts nicely with the blue tint of the nearby bright star Regulus.

About 45 minutes before sunrise look for the elusive planet Mercury in the gathering twilight. You’ll find Mercury about 10 degrees east of the bright star Spica over the next several mornings. Mercury reaches greatest elongation west of the Sun on the 17th for his best morning apparition of the year. See if you can spot him on one of the upcoming crisp autumn dawns.