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

Spring Has (almost) Sprung!

by Geoff Chester, USNO Public Affairs
15 March 2022

Orion and contrails, imaged 2022 March 14 from Alexandria, Virginia
with a Canon EOS Rebel SL2 DSLR.

The Moon wends her way into the rising stars of spring, starting the week in the constellation of Leo, the Lion, then passing through the sprawling constellation of Virgo before ending the week in the obscure stars of Libra.  Full Moon occurs on the 18th at 3:18 am Eastern Daylight Time.  The Full Moon of March goes by many names, each of which pays homage to the arrival of boreal spring.  The most common name is the Worm Moon, as earthworms are stirring in the thawing soil as the Sun warms the ground.  It is also known as the Crow Moon, Plough Moon, and Sap Moon.  Look for the second-magnitude star Porrima near the rising Moon on the evening of the 18th.  Luna will inch closer to the star as the evening turns into the morning of the 19th, hiding the star for observers in Virginia and points north.  On the following night the Moon rises with the bright star Spica.

The vernal equinox occurs on the 20th at 11:33 am EDT.  At that moment the Sun reaches an ecliptic longitude of zero degrees.  It is also the time when the center of the Sun’s disc crosses the celestial equator into the northern half of the sky.  Residents of the Amazon River delta will see the Sun directly overhead at this time.

While the equinoxes mark the beginning of a season, they are also the times when we see the most rapid change in the length of daylight in both spring and autumn.  For those of us coming out of the long nights of winter, the Sun’s northerly excursion adds just over 2.5 minutes of light to the length of each successive day.  The flip side of this is that the nights are becoming successively shorter, hastening the departure of winter’s constellations.  Daylight Time has given the stars of winter a brief reprieve, but if you want to enjoy the bright stars off Orion you only have a few more weeks before he leaves the dark night sky.  This week he sets at midnight local time. 

As Orion and his bright winter cohorts exit the sky, they are replaced by somewhat dimmer stars that form some familiar patterns.  High in the northeast is where you will find the seven stars that make up the asterism known as the Big Dipper.  After Orion, this is probably the most recognized star pattern in the northern hemisphere sky.  While its stars are generally of second magnitude, they are visible from near-urban locales.  Under dark-sky conditions, the Big Dipper appears in the context of its full constellation of Ursa Major, the Great Bear.  The two stars that form the end of the Dipper’s “bowl” provide a convenient signpost to locate other springtime stars.  If you draw an imaginary line from these stars toward the north, you will run into Polaris, the North Star.  Extending the same line to the south will guide you to Regulus, the brightest star in Leo, the Lion.  I always look forward to seeing these two constellations since they offer a variety of targets for small telescopes.  

Late in the evening another springtime feature rises in the northeast.  If you follow the “arc” of the “handle” of the Big Dipper you will find the solitary bright star Arcturus, whose rosy tint has always been a sure sign of warmer evenings for me.  Arcturus is the brightest star in the northern hemisphere sky and fourth-brightest in the entire heavens.  It is the brightest luminary in the constellation of Bo├Âtes, the Herdsman.  Most of the constellation is made up of fainter stars, but from a dark site it reminds me of an ice cream cone, a sure harbinger of warmer weather to come.

Early risers have a good reason to get up before the Sun as the bright planets are gathering in the southeast as morning twilight begins to brighten the horizon.  You should have no trouble spotting Venus, which blazes away in the star-poor regions of Capricornus.  Just southwest of Venus is ruddy Mars, which should be an easy target for binoculars in the brightening sky.  Both Venus and Mars are drawing a bead on Saturn, whose yellow hue should be brighter than Mars.  The trio will continue to converge over the next couple of weeks and will be joined by the waning crescent Moon before dawn on the 28th.
 
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