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The Sky This Week, 2018 December 26 - 2019 January 2

Happy New Year!
Orion and Sirius, imaged 2014 Marchh 27 from Paris, Virginia.
Orion and Sirius, imaged 2014 Marchh 27 from Paris, Virginia
imaged with a Canon EOS Rebel T2i DSLR.

The Moon wanes in the morning sky this week, coursing her way through the rising stars of spring.  Last Quarter occurs on the 29th at 4:24 am Eastern Standard Time.  Luna begins the week just south of the constellation of Leo, the Lion.  On the morning of the 30th she passes several degrees north of the first-magnitude star Spica.  You’ll find her near the dazzling planet Venus on the mornings of the 1st and 2nd.  On the morning of the 3rd look for the Moon’s slender crescent just three degrees from Jupiter, now becoming visible in the southeast as morning twilight gathers.  The pair will be about 10 degrees high an hour before sunrise.

If you’ve been avidly watching the sky over the past few weeks you’ve probably noticed that the time of sunset is now about 10 minutes later than it was back on December 7th.  That said, we have yet to see the latest sunrise.  That won’t occur until January 4th here in the Washington, DC area.  Rest assured, though, that the days are gradually becoming longer as Old Sol slowly begins to trek northward along the ecliptic.  New Year’s Day will be four minutes longer than it was on the solstice.

The New Year begins with an interesting astronomical event.  For those of us who like to stay up to see the calendar flip another digit, go outside at local midnight and look to the south.  You should notice a bright, blue-tinted star about 35 degrees above the horizon.  This is the star Sirius, the brightest star in the night sky.  Sirius is so bright because it is one of the closest stars to our Sun.  It is located a mere 8.6 light-years away, and as such is the sixth-closest star to us.  Only Alpha Centauri is closer among the stars visible to the naked eye.  Sirius is not only a marker of our New Year; it was also a vital sign of the changing seasons to the ancient Egyptians.  As it turns out, through a curious quirk of Nature, Sirius would appear in the morning sky just before sunrise shortly before the annual flood of the Nile brought rich nutrients to the river valley to begin the annual cycle of inundation, planting, and harvesting, the three primary seasons in the Egyptian year.  As a star, Sirius is about twice as massive as the Sun and is about 25 times as luminous.  It is gradually moving closer to us, and it will be closest to us in some 60,000 years.  It will then begin to recede, losing its place as our brightest nighttime star in about 200,000 years.  As with many stars, Sirius has a companion.  In 1844 German astronomer Friedrich Bessel noted irregularities in the proper motion of Sirius across the sky, suggesting that it had an unseen companion.  This was proven in 1862, when the American telescope maker Alvan Graham Clark discovered a faint companion while star-testing a new telescope lens.  The companion, affectionately known today as “The Pup”, was the first “white dwarf” to be discovered.  The Pup is a “degenerate star” in which gravity has overwhelmed the nuclear radiation pressure that kept it stable over most of its life.  The powerful force caused the star to collapse to an object of about one solar mass that is about the size of the Earth.  A thimble of this material would weigh about as much as a nuclear aircraft carrier!  Sirius’ bright blue tint is due to the star’s hot surface, which glows at about twice the temperature as the surface of the Sun.

The first meteor shower of the year peaks on the night of January 3-4.  Known as the Quadrantids, they are named for the now-defunct constellation Quadrans Muralis, once located between the bright star Arcturus and the end of the “handle” of the Big Dipper.  There will be no moonlight to interfere with their visibility this year.  The shower is quirky, as its peak activity only lasts a few hours.  Typical dark-sky hourly rates are about 25, but occasionally they will “storm” at well over 100 per hour.

Mars greets the new year from a perch in the constellation of Pisces and is easily found in the west in the southwest during the early evening hours.  He continues to trek eastward along the ecliptic.

Venus gets a visit from the Moon as 2019 begins.  Luna’s slender crescent and the bright glow of Venus will provide great photo opportunities for pre-dawn skywatchers on the 1st and 2nd.

If you have a flat southeastern horizon look for the return of bright Jupiter about an hour before sunrise.  The Moon will be close by the giant planet on the morning of the 3rd.  Old Jove will gradually work his way back to the evening sky next summer.

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