The Sky This Week
U.S. Naval Observatory's Weekly Blog

A Binocular Tour of the Winter Sky

by Geoff Chester, USNO Public Affairs
09 February 2021
Messier 37, open cluster in Auriga, imaged from Old Tavern, Virginia on 2017 December 17
Messier 37, open cluster in Auriga, imaged from Great Meadow Park, Old Tavern, Virginia on 2017 December 17
with an Explore Scientific AR-102 10.2-cm (4-inch) f/6.5 refractor and Canon EOS Rebel T2i DSLR.

The Moon returns to the evening sky by the week’s end.  New Moon occurs on the 11th at 2:05 pm Eastern Standard Time.  Try to spot Luna’s hairline crescent during evening twilight on the evening of the 12th.  Over the next few evenings look for the phenomenon called “earthshine”, where the part of the Moon’s disc that’s not in direct sunlight reflects light from our home planet.  This ghostly blue glow is best seen during the early crescent lunar phases.

We are now approaching the time of year when the length of daylight changes most rapidly.  By the end of the week the Sun sets an hour later than it did back in December and sunrise occurs half an hour later than it did in early January.  Each passing day brings about 2.5 minutes’ more daylight, and that rate will gradually increase until the vernal equinox on March 20th, when it will amount to over three minutes per day.  

We see this change reflected in the night sky as well.  The stars of the Great Winter Circle cross the meridian between 7:30 and 10:00 pm making way for the first of spring’s star patterns.  You still have lots of time in the early evening to enjoy the colorful stars of winter and the many subtle treats that lie behind them.  This is a great part of the sky to explore with binoculars, with many objects to delight both urban and rural skywatchers.  High in the west you will find the famous Pleiades star cluster, a small knot of stars that has been the subject of lore and legend for civilizations across the millennia.  To the naked eye in a dark site it looks like a tiny version of the “Big Dipper”, with six of seven stars typically visible.  Binoculars begin to reveal the true nature of this group as dozens of fainter stars come into view.  Modern astronomical techniques have identified over 1000 stars as members of the cluster.  It is located about 440 light-years away.

Our next binocular target is easily found among the stars of Orion.  Just south of the Hunter’s “belt” of three stars you will see a small asterism known as “The Sword”.  Point your binoculars at the middle star in this group and you will see the wispy light of the Great Orion Nebula.  This glowing cloud is a stellar factory that has spawned most of the bright blue stars that make up Orion’s familiar shape.  Easily seen from suburban yards, the view from a darker site is even more spectacular.  The nebula is surrounded by ice-blue stars set on a velvet background filled with faint shimmers of nebulosity.  It 8is about 1300 light-years away. 

From a dark site you should be able to see the subtle star-clouds of the Milky Way just to the left of Orion.  Let your gaze follow the glow to the zenith and the bright yellow star Capella in the constellation of Auriga, the Charioteer.  Sweep the area between Capella and the constellation’s second-brightest star El Nath (which also marks the tip of Taurus’ northern “horn”).  Here you will find three bright star clusters that will just begin to resolve in your binoculars.  Known as Messier 36, 37, and 38, these rich clusters lie at distances from 3500 to 4500 light-years.  They are excellent targets for small telescopes, especially M37, which resolves into hundreds of stars.

Our final binocular stop is yet another star cluster that is located in the somewhat obscure springtime constellation of Cancer, the Crab.  This group of faint stars resides between Castor and Pollux in Gemini and Regulus in the constellation of Leo, the Lion.  By 11:00 pm Cancer is near the meridian; sweep the area halfway between Pollux and Regulus with your binoculars to locate a scattered group of stars that form the cluster known as the Praesepe, or The Beehive.  In binoculars the cluster is a pleasing sight, set between four brighter stars.  You should be able to see a few dozen stars in the cluster from a dark site

Lonely Mars continues his vigil in the evening sky.  You will find him just over 10 degrees west of the Pleiades, and during the course of the week he closes in on the cluster.  He won’t be lonely for very long, as three emissaries from Earth arrive over the next several days.  Space probes from the United Arab Emirates, China, and the U.S. arrive between now and the 18th.

 
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