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The Sky This Week, 2017 December 5 - 12

The solstice season is upon us.
M38_161231_01small.jpg
Messier 38 and NGC 1907, open clusters in Auriga
imaged from Mollusk, Virginia on 2016 December 31
with a 4-inch f/6.6 Explore Scientific AR102 refractor and a
Canon EOS Rebel T2i DSLR camera.

The Moon moves into the morning sky this week, drifting from the eastern bounds of the Great Winter Circle through the rising stars of the springtime sky.  Last Quarter occurs on the 10th at 2:51 am Eastern Standard Time.  If you’re up for an early morning treat, try to find the binocular star cluster known as “The Beehive” just two degrees above the Moon on the morning of the 7th.  Formally known as Messier 44, this cluster can be seen with the unaided eye from a dark, moonless location, but it should be easy to spot in binoculars when Luna or a bright planet are nearby.  Over the next two mornings the Moon will pass near the bright star Regulus.  As the week ends, look for Luna’s waning crescent in the company of the bright star Spica and the red planet Mars.

This week kicks off the phenomena that surround the winter solstice.  We’re all familiar with the solstice itself, which is the date of the shortest day and longest night in the Northern Hemisphere.  It typically falls on December 21st or 22nd, depending on where we are in the calendar leap-year cycle.  However, it isn’t the date that we observe the latest sunrise or earliest sunset.  Thanks to the slight eccentricity of the Earth’s orbit around the Sun, we are actually experiencing the year’s earliest sunsets this week.  Here in Washington, Old Sol slips below the horizon at 4:46 pm EST, and he will continue to do so until the 12th, when he slowly begins to set a little later each day.  By Christmas he will set at 4:52 pm, and by January 4th he’ll set at 5:00 pm.  The year’s latest sunrise won’t occur until January 5th, when the Sun lollygags until 7:27 am EST before peeking over the horizon.  We have a detailed explanation for this interesting phenomenon on our website.  The same effect occurs over a two-week interval centered on the summer solstice.

As The Moon moves into the morning sky early evening skywatchers can search for darker skies to enjoy the interesting features of the autumn sky.  Hovering hear the zenith at around 8:00 pm is the most distant object visible to the unaided eye, the Great Andromeda Galaxy.  If you can spot the Milky Way look overhead for a small hazy patch that looks like a detached portion of our home galaxy.  In reality it is a galaxy in its own right, a swirling mass of some 400 billion stars located some 2.5 million light-years from us.  It stubbornly resists resolution into stars in all but the world’s largest telescopes, appearing as a diffuse glow in binoculars and amateur instruments.

Follow the path of the Milky Way as it arcs over the northern sky.  Scattered among the stars of Cassiopeia, Perseus, and Auriga are a host of wonderful star clusters.  They show up as knots of light in binoculars but yield their true character in telescopes of four or more inches of aperture.

The only bright planets that are easily visible right now are Mars and Jupiter, which are best seen as morning twilight begins to gather.  You’ll find them in the southeastern sky at 6:00 am EST with ruddy Mars close to the bright star Spica.  Jupiter is lower but much brighter than his ruddy friend, and if you watch the pair during the course of the week you’ll notice Mars closing ranks with the giant planet.  They will have a spectacular close conjunction on January 7th.

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