The Sky This Week
U.S. Naval Observatory's Weekly Blog

Counting Stars for Science!

by Geoff Chester, USNO Public Affairs
02 March 2021

Orion & Sirius, 2020 January 1, imaged from Mollusk, Virginia
with a Canon EOS Rebel SL2 DSLR, EF-S 18-55mm f/3.5-5.6 zoom lens, and
an Omegon MiniTrak LX2 manual star tracker

The Moon dives southward along the ecliptic this week, mingling with the spring constellations and the first rising stars of summer.  Last Quarter falls on the 5th at 8:30 pm Eastern Standard Time.  Early risers can catch Luna among the stars of Scorpius, just north of the bright star Antares, before dawn on the 5th.  As the week ends the Moon closes in on a gaggle of planets lying low over the southeast horizon as twilight begins to brighten the sky.  

The March citizen-science observing campaign for the Globe at Night project kicks off on the evening of the 5th and runs through the 14th.  2020 was a record year for the program, which began in 2006.  Over 29,000 observations were reported from observers around the world, and over the years the program has had responses from people in 180 countries.  Part of the program’s success last year can be tied to the coronavirus, which has prompted many people to seek outdoor activities near their homes.  There has been a “boom” in interest in amateur astronomy as people realize that being quarantined doesn’t limit you to your home when the universe is literally over your head every clear night.  

Participating in Globe at Night is very easy.  Find the month’s featured constellation, go outside and let your eyes adapt to the darkness, then compare your view of the sky with the charts posted on the Globe at Night website.  This month’s featured constellation is Orion, which can be seen from every inhabited part of the planet.  The Hunter’s bright, distinctive pattern is almost universally recognized, and his outline can be seen from just about any location including the centers of major cities.  Your report to the website will help scientists determine the amount of light (and wasted energy) is escaping our planet into space.

Orion is well-placed in the early evening, just west of the meridian at 8:00 pm local time.  He is perhaps my favorite constellation because of his distinct shape and the colorful bright stars that delineate him.  He is a real treat for owners of small telescopes which accentuate the ruddy glimmer of Betelgeuse and the icy blue of Rigel and the “Belt Stars”.  Just below Orion’s belt is a small gathering of stars that are easy to spot in your telescope’s finder.  The middle “star” in this clump marks the location of the Great Orion Nebula, one of the few “deep sky” objects that can be seen well from urban locations.  The nebula appears as a softly glowing cloud surrounding a group of four stars known as the Trapezium.  These stars are very young and very energetic.  Most of their radiation falls in the ultraviolet portion of the spectrum, and this radiation causes the gas in the surrounding nebulosity to glow.  Above and below the nebula are other loose clusters of stars that glimmer like tiny diamonds against the inky background.

Following Orion across the sky is Canis Major one of his two hunting dogs.  This grouping boasts the brightest star in the night sky, Sirius.  Although the star’s name is derived from the Greek word for “scorching” it is popularly known as the Dog Star.  Watching it drift through the telescope field is a bit like watching a mini-sunrise.  The field begins to brighten as the star draws nearby, then bursts with an explosion of bright blue light when it enters.  Scintillation caused by air currents often makes Sirius dance through the colors of the rainbow, flickering like a distant candle.

Lonely Mars is still the only bright planet in the evening sky.  He continues to drift eastward through the sky against the background stars of Taurus, the Bull.  He is now a tad dimmer than the nearby star Aldebaran, and he spends the week passing between the star and the Pleiades star cluster.  This should present a fine photo opportunity for novice astrophotographers.

If you’re willing to get up before the Sun, three planets will greet you in morning twilight.  Saturn, Jupiter, and Mercury all gather in the southeast, but you will need a good flat horizon and very clear skies to glimpse them.  The best time to look for then is at the end of the week, when the waning crescent Moon joins them on the mornings of the 9th and 10th.  If you can spot Jupiter on the morning of the 5th you will find Mercury close by to the left of the giant planet.
 
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