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The Sky This Week, 2020 February 18 - 25

Moonlight, mangers, and manes.
Orion and Sirius, 2014 March 27, imaged from Paris, Virginia.
Orion and Sirius, 2014 March 27, imaged from Paris, Virginia
with a Canon EOS Rebel T2i DSLR.

The Moon spends the week as a thin crescent in twilight, waning in the morning sky as the week opens and waxing in the evening sky as the week ends.  New Moon occurs on the 23rd at 10:32 am Eastern Standard Time.  Look for the very slender waxing crescent Moon low in the west half an hour after sunset on the 24th.  Luna cozies up to dazzling Venus on the evenings of the 26th and 27th.

The February Globe at Night observing campaign continues this week, with Orion as the featured constellation to view.  Orion crosses the meridian at 8:00 pm, which places him in the perfect position to count the number of stars you can see from your location.  It is also a constellation with stars that cover a wide range of brightness, so star counts can be easily made from the heart of the city or from the darkest sky you can find in rural areas.  All you need to do is find an unobstructed view of the sky away from the direct glare of street lights, let your eyes adapt to the darkness for about 15 minutes, then compare your view of Orion with star charts on the Globe at Night’s web app.  This “citizen science” program has now been going strong for over 10 years, and it has been instrumental in helping scientists measure the encroachment of artificial light on the night sky.  Data from the Globe at Night program has been a great help in establishing “dark sky parks” around the nation and the world, so please take a few minutes from your evening activities to help preserve our night sky.

As the evening grows later, the stars of winter are gradually being replaced by some of the rising stars of spring.  The easternmost stars of the Great Winter Circle cross the meridian by 10:00 pm in the form of the Twin Stars of Gemini, Castor and Pollux, and the star Procyon in Canis Minor.  To the east of Procyon is the star Regulus, the heart of Leo, the Lion, one of the more distinctive constellations of spring.  Between Leo, Gemini, and Canis Minor there is a scattering if faint 3rd- and 4th-magnitude stars that betray the constellation of Cancer, the Crab.  Normally this area of the sky wouldn’t attract much attention, but if you’re out at a good dark sky site you may notice a small, cloudy patch of light among the scattered stars.  Binoculars will show that this “cloud” is really a star cluster that was known to the ancient Greeks and Romans as the Praesepe, or “the manger”.  Today it is most popularly known as “the beehive”, and binoculars will reveal it to be a fairly rich swarm of faint stars.  Located at a distance of about 577 light-years, large telescopes have identified some 1000 stars as cluster members.  A modest amateur telescope will show several dozen of the cluster’s brighter members, and it is perennial favorite at springtime star parties.

Turning our attention to Leo, we find a large constellation that actually resembles its namesake.  North of Regulus, the Lion’s regal head and mane is formed by a semicircular arc of 2nd- and 3rd-magnitude stars, while his haunches are delineated by a right triangle asterism just over 15 degrees east of Regulus.  The constellation’s second-brightest star, Algeiba, lies just north of Regulus and shines with a delicate yellow hue.  Point a telescope at Algieba and you will see a fine double star consisting of a close pair of golden suns with about one magnitude difference in brightness.  This is a typical physical binary pair, with an orbital period that takes the stars around their center of mass in about 550 years.  It is one of my favorite objects to view in my 4-inch refractor.

Venus beams down brightly from the western sky during the evening hours.  She pops into view shortly after sunset, and once the sky gets fully dark it almost hurts your eyes to look at her.  From very dark locations she casts enough light to throw shadows, especially on a whiteboard on the ground.  She will welcome the waxing crescent Moon early next week.

Most of the planetary action takes place in the pre-dawn sky, where ruddy Mars and bright Jupiter cavort in the stars of summer constellations.  Mars drifts eastward over the top of the “teapot” asterism of Sagittarius.  By the week’s end Mars passes just under two degrees to the north of Kaus Borealis, the star that marks the teapot’s “top”.  Jupiter follows Mars and slowly drifts under the “teaspoon” asterism of faint stars in a view that should be a treat for binocular observers.