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The Sky This Week, 2020 March 24 - 31

Lions, no tigers, and bears, oh my!
The Moon, Mars, & Jupiter, imaged 2020 March 18, 10:34 UT from Alexandria, Virginia.
The Moon, Mars, & Jupiter, imaged 2020 March 18, 10:34 UT
From Alexandria, Virginia with a Canon EOS Rebel SL2 DSLR

The Moon returns to the evening sky this week, waxing through her crescent phases as she climbs toward the departing winter constellations.  First Quarter occurs on April 1st at 6:21 am Eastern Daylight Time.  Luna joins Venus for a beautiful grouping with the Pleiades star cluster on the evening of the 28th.

Since most of us are homebound for the foreseeable future and unable to follow our routines, perhaps it is a good time to make a little time in your evenings to step out and enjoy the night sky and the sights it has to offer.  The Moon is a great place to start.  It is the closest place to the Earth in the solar system, but it’s far enough away that light takes about 1.2 seconds to traverse the distance.  It is a great target for binoculars and small telescopes, presenting the observer with a myriad of interesting features.  As the phase increases from night to night different formations are revealed as the terminator line slowly progresses eastward.  Binoculars suffice to show the major features like the smooth lunar “seas” and the larger craters, but a very modest telescope will reveal much finer detail.  Now the craters take on their unique appearances, and the number of craters that you’ll see will increase exponentially.  On the evening of the 29th you will find two very prominent impact craters near the middle of the terminator which can be easily seen in binoculars.  They seem to be conjoined, with the younger formation known as Theophilus overlapping its older twin Cyrillus.  In a telescope you should be able to see the prominent central peak in Theophilus and perhaps begin to get a sense of the enormous scale of the features.  They are just over 100 kilometers (60 miles) across, and you’ll notice that they lie on the edge of one of the lunar “seas”, Mare Nectarum, the “Sea of Nectar”.  This feature, along with the other prominent “seas” of the lunar nearside, is also a remnant of an enormous impact that occurred about 3.9 billion years ago.  Theophilus, by contrast, is a veritable newcomer.  It’s only about a billion years old!

As the nights grow shorter we have less time to enjoy the departing winter constellations.  You will find Orion in the southwest as evening twilight fades, and the late evening he’s beginning to dip his toes below the horizon.  Orion has been a great target for naked-eye observing this season.  The ruddy star Betelgeuse, normally nearly as bright as blue-tinted Rigel, surprised astronomers around the world by fading to a deep minimum in brightness that reached its nadir in mid-February.  Betelgeuse has long been known to vary in brightness, but this fade was very unusual as the star shone at half of its normal glory.  At its faintest I estimated it to be comparable to the star Alnitak, left-most star in Orion’s “belt”, but it is now brightening back to its rightful place as the constellation’s second-brightest star.  Astronomers are still seeking a good explanation for this unusual behavior, but Betelgeuse is a very evolved star and its structure is quite unstable.  We’ll just have to wait and see what it does by next winter.

The spring sky brings the familiar outline of the Big Dipper into prominence.  By 11:00 pm it is close to the meridian and at its highest point in the northern sky.  The Dipper is part of the much larger constellation of Ursa Major, the Great Bear.  If you look past the zenith to the south you will see the sickle-shaped asterism that outlines the head of Leo, the Lion, led by the bright star Regulus.  Sharing this part of the sky are two more cat constellations, Leo Minor and Lynx, but, sadly, there are no tigers.

Venus is marching relentlessly northeastward along the ecliptic to join the winter constellations.  You should have no trouble finding her as soon as the Sun sets, and if you know where to look she can be seen in a clear daytime sky.  Watch her move toward the Pleiades star cluster this week.  Next week she will pass through the cluster!

Ruddy Mars passed Jupiter last week, shortly after a spectacular grouping with Old Jove and the Moon.  This week he sets his sights on Saturn, passing the ringed planet by the week’s end.  At their closest they will be less than a degree apart, then Mars will desert the gas giants as he moves into the stars of Capricornus.  Rise before the Sun to catch this planetary parade.