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The Sky This Week, 2018 February 13 - 20

View the waxing Moon and the rising stars of spring.
The Old Moon in the arms of the New Moon, 2018 January 20
imaged from Alexandria, Virginia with a 10.2-cm (4-inch) f/6.5 Explore Scientific AR-102 refractor
and a Canon EOS Rebel T2i DSLR.
HDR composite of four images, 1/500s, 1/125s, 1/30s, and 1/8s exposures.

The Moon returns to the evening sky this week, appearing as a slender crescent in the evening twilight before climbing rapidly as she waxes toward the First Quarter phase.  This will occur on the 23rd at 3:09 am Eastern Standard Time.  You have an excellent opportunity to catch the day-old crescent on the evening of the 16th.  Half an hour after sunset look for Luna’s hairline-thin crescent about 4 degrees above the western horizon.  If you have an unobstructed view to the west try to spot bright Venus in the twilight glow about two degrees below and to the right of the Moon.  Over the course of the next few evenings, watch Luna’s crescent grow.  In particular look for the phenomenon of “Earthshine”, the soft blue glow that bathes the segment of the lunar disc that’s not illuminated by sunlight.  Popularly called “the old Moon in the arms of the new Moon”, the late winter and springtime months are the best times to view this subtle feature.

As the Moon encroaches on the evening sky she starts to wash out the last of the faint autumn constellations, then sets her sights on the bright stars of the Great Winter Circle.  Orion and his bright cohorts dominate the early evening sky, crossing the meridian between 8:00 and 9:00 pm.  By the week’s end the Moon sets at around 10:00 pm, and winter’s stars are beginning to set in the west.  In the east we can start to look for some of the signature signs of the coming spring.  Two star patterns to look for at this time are the familiar outline of the “Big Dipper” and the crouching feline constellation of Leo, the Lion.  The Dipper is wheeling into the northeastern sky with its “handle” pointing toward the horizon.  The seven stars that make the Dipper asterism are probably the second-most recognized group of stars in the sky after Orion.  Although none of the Dipper’s stars shine above second magnitude, they do form a very distinctive pattern.  The asterism is part of the much larger constellation of Ursa Major, the Great Bear.  From a dark location the fainter stars of the constellation outline a fairly credible ursine shape.  Leo sports a first-magnitude star, Regulus, which stands high in the east at 10:00 pm.  To the north of the star an arc of second- and third-magnitude stars outline the lion’s head; a right triangle of stars between Regulus and the horizon depict the lion’s hindquarters.  

Owners of small telescopes have a number of interesting things to look at in these constellations.  Point your scope at the second-magnitude star a few degrees to the left of Regulus.  Known as Algieba, it is a beautiful golden-hued star that resolves into a closely-spaced pair of yellow suns.  In the Dipper, locate the star that forms the bend in the “handle”.  This star, Mizar, has a faint companion, Alcor, that serves as a test of your naked-eye vision.  In the telescope, Mizar itself is an easily resolved pair of whitish-blue stars.  It was the first non-solar system object that I observed with my first telescope, a 60-millimeter refractor, many years ago.  As it turns out, both components are spectroscopic binaries.  The A-component has been resolved with the USNO’s Navy Precision Optical Interferometer at Anderson Mesa in Arizona.

Early risers still have the best view of the planets this week.  At 6:00 am you’ll find Jupiter on the meridian forming a triangle with the two brightest stars of Libra.  They aren’t particularly bright, but you’ll occasionally find them in the crosswords.  Their names are Zubenelgenubi and Zubeneschamali.  To the east of Jupiter you’ll find ruddy Mars, trekking eastward above the first-magnitude star Antares.  Saturn brings up the rear, perched directly above the rising “Teapot” asterism formed by the brightest stars of Sagittarius, the Archer.