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The Sky This Week, 2018 February 27 - March 6

A bright star returns, and Venus creeps into the evening sky.
Moon_171204_0252_01.jpg
Just past Full Moon, 2017 December 4, 02:52 UT
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.

The first of two Full Moons for the month of March lights up the sky this week, escorting the springtime constellations into the sky.  Full Moon occurs on March 1st at 7:51 pm Eastern Standard Time.  This Full Moon is popularly known as the Snow Moon or Hunger Moon.  March will experience its second Full Moon on the 31st, making this one of those unusual years when January and March each have two Full Moons while February has none.  We’ll have to wait another 19 years for this to occur again.  Luna will wash out many of the fainter stars of the springtime sky, but you should be able to spot the bright star Regulus just east of the Moon’s nearly full disc when they rise on the evening of the 28th.  Luna will pass just to the north of Regulus at around 1:00 am EST on the 1st.  She pays a visit to the bright star Spica on the morning of the 5th, and pre-dawn skywatchers can find her in the company of Jupiter as twilight gathers on the morning of the 7th.

The bright winter constellations are now crossing the meridian at the end of evening twilight.  By midnight the stars of Taurus are slipping below the horizon, and Orion follows an hour later.  Enjoy these colorful stars while you can since we now gain almost three minutes of daylight each day as the Sun climbs northward toward the equinox.  All too soon these brilliant luminaries will be replaced by the more subdued stars and constellations that mark the coming of spring.  One star stands out in the springtime sky, though, and you can find it rising in the east shortly before 9:00 pm.  Arcturus is the brightest star in the northern hemisphere sky and the fourth brightest of all the stars.  It is characterized by a slight amber tint, although it may flash through multiple colors as its light passes through the dense layer of air above the horizon.  We can look at Arcturus and get something of a “preview” of the fate of the Sun.  Arcturus is about 3 billion years older than Old Sol and has exhausted the supply of hydrogen that fuses to helium in its core.  Hydrogen now fuses in a shell around an inert core of helium “ash” which has caused Arcturus’ girth to swell to some 25 times that of the Sun.  In turn, its larger surface area means that it is about 170 times as bright as the Sun but its surface temperature is cooler.  This gives Arcturus its characteristic color.  It is located just under 37 light-years away and has the fastest “proper motion” against more distant stars than any other first-magnitude star.  It was one of the first stars to have its proper motion measured.  In 1718 Edmond Halley found that it had moved about half a degree, the apparent diameter of the Moon’s disc, since the era of the ancient Greek astronomer Hipparchus, who compiled the first accurate catalog of star positions some 1800 years earlier.

Venus is gradually working her way up from the horizon into the evening sky.  She is still only visible in the glow of evening twilight, but by the end of the week she sets over an hour after sunset.  You’ll find her about five degrees above the west-southwest horizon.  Mercury joins Venus by the weekend.  Use binoculars to locate the fleet planet, which will lie just a degree to the right of much brighter Venus on the evening of the 4th.

I found myself awake at 5:30 this morning, so I set up the telescope to catch a glimpse of Jupiter before sunrise.  The giant planet is just past the meridian at this time, and I was treated to a nice view of the planet, his four Galilean moons, and the tiny shadow of the moon Europa slowly skimming over the cloud tops.  Just east of the meridian I found the ruddy star Antares and even redder Mars, easily spotted as the sky began to brighten.  Saturn brought up the rear, a yellow-hued glimmer above the “Teapot” of Sagittarius.  These three planets will all be well-placed in the evening sky during the summer months, but it’s till nice to see them in the pre-dawn sky with the chirping of springtime birds providing the sound track.

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