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The Sky This Week, 2017 November 27 - December 4

Seven sisters and a winking star.
The Pleiades, imaged 2016 December 31 from Mollusk, Virginia.
The Pleiades, imaged 2016 December 31 from Mollusk, Virginia.
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.6 refractor and a Canon EOS Rebel T2i DSLR.

The Moon moves from the Great Winter Circle into the rising stars of the springtime sky, gracing the pre-dawn hours.  Last Quarter occurs on the 29th at 7:19 pm Eastern Standard Time.  Look for the bright star Regulus less than two degrees south of the Moon on the morning of the 29th.  By the week’s end her waning crescent cavorts with dazzling Venus during the pre-dawn twilight.  

As Luna drifts into the early morning sky it’s once again time to do a little “citizen science” under the stars.  November 29th marks the beginning of the penultimate “Globe at Night” monthly observing campaign for 2018.  This month we once again feature the constellation of Perseus, which lies just north of the zenith at around 10:00 pm.  Perseus resembles a “winner’s portion” of a wishbone and is anchored by the bright second-magnitude star Mirfak.  The constellation lies between the “W”-shaped grouping of Cassiopeia and the bright star Capella.  To record your observation of the number of stars that you can see in Perseus, wait about 15 to 20 minutes under the stars to adapt your night vision, then compare the stars you can see to the charts on the Globe at Night website.  While you’re at it, look for some of the interesting sights in and around the constellation.  One of the most fascinating is the star that is normally the constellation’s second-brightest member, Algol, the “Demon Star”. In mythology the star represents the severed head of the Gorgon Medusa, slain by Perseus in one of his more heroic exploits.  The star usually shines just a bit fainter than Mirfak, but every 2.87 days it fades by over a full magnitude and remains dim for several hours.  The star will be at minimum brightness on November 30th at 12:02 am EST and again on December 3rd at 8:51 pm EST.  If you have binoculars handy, look just five degrees west of Algol for a fuzzy knot that betrays the position of Messier 34, one of the autumn’s best galactic star clusters.  It is a real treat to observe in a small telescope.  Another binocular treat surrounds the star Mirfak, which sits in the middle of a sprawling scattering of stars known as Melotte 20.

If you follow the long “tine” of the Perseus “wishbone”, you’ll run into one of the most storied groupings of star in the sky.  We know it as The Pleiades or Seven Sisters, and it is a fixture in the skylore of just about all cultures that inhabit the Earth’s northern hemisphere.  In Greek mythology the diminutive group represents seven daughters of Atlas, who were continually evading the amorous attentions of Orion.  To relieve them of this incessant pursuit Zeus turned the sisters into doves and placed them in the sky, safely out of The Hunter’s reach.  The Pleiades form a true star cluster some 440 light-years distant, and its stars are some of the youngest known in our galaxy.  Long-exposure images still show the remnant clouds of gas and dust that formed the cluster’s constituent stars.  Under favorable conditions most of us can see six or seven cluster members with our unaided eyes, while some keen-eyed observers can spot a dozen.  Telescopes of increasing apertures reveal more stars, and the latest surveys with space-based instruments have determined that over 1,000 stars make up the group.  The vast majority of these are very faint “brown dwarf” stars, barely visible in our most sensitive instruments.  The brightest members shine with an icy-blue tint, and are one of my favorite sights in my low-power 4-inch refractor telescope.

Saturn is just barely visible in the fading twilight of the early evening.  The ringed planet sets shortly after evening twilight ends, so you’ll be hard pressed to find him against a dark sky.  He will reach conjunction with the Sun just after the start of the new year.

Mars is now the only bright planet visible in the evening sky.  He now shines at zero magnitude, some 10 times less intense than he was at opposition last summer, but his location among the faint stars of Aquarius makes his ruddy tint stand out in the deepening evening twilight.  You’ll find him in the south at around 6:00 pm, and he sets shortly before midnight.  This week he closes in on the 3rd-magnitude star Lambda Aquarii, passing within a degree of the star on the evenings of the 3rd and 4th.  This week Mars welcomed a new emissary from Earth, the Mars InSight lander, which settled gently onto a smooth plain in the region known as Elysium.  Mars InSight will spend the next two years studying the interior of the red planet, hopefully revealing secrets about Mars’ formation.

Venus beams down from the southeastern sky as morning twilight begins to brighten the sky.  She is at her brightest for the current morning apparition, so you should have no trouble spotting her as the sky lightens.  d her in the vicinity of the bright star Spica for the duration of the week.  Look for the waning crescent Moon nearby on the mornings of the 3rd and 4th.

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