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The Sky This Week, 2019 February 12 - 19

More looking at the Moon
The Moon, imaged 2018 January 25 from the U.S. Naval Observatory, Washington, DC
The Moon, imaged 2018 January 25 from the U.S. Naval Observatory, Washington, DC
with the 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor
and a Canon EOS Rebel T2i DSLR. Composite of 10 images.
Mare Imbrium is the large circular feature to the upper left.
The crater Copenicus is on the terminator near the left center.

The Moon courses through the bright stars of the Great Winter Circle this week, brightening the night sky as she waxes toward Full Moon, which will occur on the 19th at 10:53 am Eastern Standard Time.  February’s Full Moon is popularly known as the Hunger Moon or Snow Moon.  Look for the bright star Aldebaran about two degrees southeast of Luna on the evening of the 13th.  She will close the gap to just one degree by midnight as the 13th rolls into the 14th.

As the Moon waxes toward Full she passes along the northernmost reaches of the ecliptic, making this another great week to explore the battered surface of our nearest celestial neighbor.  When Luna is high in the sky we look through less of Earth’s atmosphere.  This allows less air to interfere with seeing the Moon’s finer details.  This week the terminator slowly reveals one of her largest impact basins, named by 17th Century astronomers as Mare Imbrium, the Sea of Rains.  This feature is easily seen by the naked eye from Earth’s surface, forming the right “eye” of the “Man in the Moon”.  Mare Imbrium is a gigantic impact feature that measures 1250 kilometers (757 miles) across.  It formed about 3.85 billion years ago when a large asteroid crashed into the surface.  This body plowed deep into the Moon’s mantle and subsequently caused lava to erupt and fill the resultant crater.  In a small telescope it looks quite smooth, but in moments of steady air smaller craters begin to show the history of subsequent impacts by countless smaller bodies.  A good 6- to 8-inch telescope will show thousands of smaller craters and pits dotting the landscape.  While looking for small craters and isolated mountain peaks, notice the so-called “wrinkle ridges” that seem to ripple across the landscapes.  On nights of exceptionally steady air you might almost think that you’re “there”, but in reality the Moon is still a long way away.  The smallest lunar features I’ve ever been able to discern are one kilometer (0.61 miles) across.  That’s about the size of the famous Meteor Crater located east of Flagstaff, Arizona.  This terrestrial feature was carved by a relatively small asteroid impact some 50,000 years ago.  Gazing across it is very impressive, but at the Moon’s distance it is little more than a small blemish in the smooth lava plains.  If nothing else, though, these barely-visible lunar features lend a sense of scale to their larger neighbors, some of which are over 100 kilometers across.  Fortunately for us these larger craters date back to around one billion years ago, telling us that the age of bombardment by larger bodies of the asteroid belt ended a very long time ago.  One of the more recent of these later impacts is well-placed on the terminator on the evening of the 13th.  The prominent crater Copernicus is one of the Moon’s more recent features, but it is nevertheless estimated to have formed 1.1 billion years ago!

Mars continues to doggedly stay ahead of the advancing Sun.  You’ll find the red planet travelling eastward along the ecliptic as he enters the constellation of Aires, the Ram.  He begins the week about one degree north of the far-flung planet Uranus before leaving the more distant world in his wake.  The two objects share the field of a low-power telescope for the first few nights of the week.   

Giant Jupiter rises at around 3:00 am in the southeast, and as the first rays of dawn begin to brighten the horizon he should be easy to find.  He will spend most of the year in this part of the sky northeast of the stars of Scorpius, slowly drifting through the constellation of Ophiuchus, the Serpent-Bearer.

Bright Venus rises at around 4:30 am, quickly calling attention away from Jupiter.  She continues to charge eastward through the stars of Sagittarius, and by the end of the week passes just one degree north of Saturn.  Use binoculars to find the ringed planet, since the pair will be competing with the growing glow of dawn.

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