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

Springtime Sky Sights, Near and Far

by Geoff Chester, USNO Public Affairs
22 March 2022

NGC 2903, a barred spiral galaxy in Leo, imaged 2022 March 22 from Shoestring Observatory, Alexandria, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6,5 refractor, iOptron AZMP alt-azimuth mount,
and a ZWO Optical ASI183MC CMOS imager. This galaxy is an outlier of the Virgo Galaxy Cluster.
It is about 30 million light-years away.

The Moon spends the week drifting along the southern reaches of the ecliptic, keeping company with the rising stars of summer in the early morning skies.  Last Quarter occurs on the 25th at 1:37 am Eastern Daylight Time.  Luna may be found just north of the bright star Antares in Scorpius on the morning of the 23rd.  On the 25th she sits in the middle of the “Teapot” asterism in Sagittarius.  If you have to choose one morning to rise well before the Sun this week it should be the morning of the 28th.  At that time the Moon’s waning crescent will be grouped with the planets Venus, Mars, and Saturn in the southeastern part of the sky.  This will be one of the best such groupings to occur in 2022.

The absence of the Moon from the evening sky signifies that it’s time for the March campaign for the citizen-science program, Globe at Night.  This program aims to engage people to be more aware of the state of the night and the growing threat of light pollution.  Now entering its 13th year, the program solicits simple naked-eye observations of the sky from the public.  So far this year over 3500 observations have been logged on the Globe at Night website, and it is hoped that by the end of the year the number of reports will surpass the 25,000+ recorded in 2021.  This month’s featured constellation is Leo, the Lion, which may be found high in the eastern sky at the end of evening twilight.  Leo consists of two distinct asterisms, the first of which is anchored by the bright star Regulus.  To the north of this star you will see a semi-circle of second- and third-magnitude stars that make up a figure commonly called “The Sickle”.  Some 15 degrees to the east of the Sickle is a right triangle whose acute angle is marked by the second-magnitude star Denebola.  Once you have found Leo, compare your view to the charts on the Globe at Night web app to record your observation.

Leo leads a group of stars that mark the transition from winter’s bright constellations to those of summer.  This part of the sky has relatively few bright stars because we are looking away from the plane of the Milky Way, our home galaxy.  Instead of seeing the layered star clouds of the Milky Way, when we look in the direction of these springtime constellations our gaze takes us into deep intergalactic space.  The spring sky has relatively few star clusters and glowing nebulae, but it abounds in external galaxies, of which several hundred are visible with modest telescopes under dark skies.  The vast majority of these galaxies are part of a group known as the Virgo Galaxy Cluster, with our own Milky Way a far-flung outlying member.  The core of this supercluster is dominated by three enormous elliptical galaxies that harbor the equivalent mass of over one trillion (yes, with a “t”) Suns.  These systems are so massive that they have distorted many of their nearby companions through tidal forces.  Fortunately for us, they are about 55 million light-years away.  While the Milky Way does feel some of their gravitational muscle, we’re far enough away from them to not feel their more catastrophic effects.  

The Virgo Galaxy Cluster covers a large area of the sky, loosely bounded by Denebola in Leo, the bright stars Arcturus and Spica, and the stars that form the “handle” of the Big Dipper asterism.  If you point a six-inch or larger telescope anywhere within this area from a dark-sky site the odds are that you will notice several fuzzy swatches of light in the eyepiece.  In and of themselves they are not very spectacular, but when you realize that you are looking at the combined light of a few hundred billion stars shining across a gulf of space and time you may begin to realize just how vast the universe is.

As we mentioned earlier, the early morning sky is where you will find all of the brighter planets this week.  Dazzling Venus and nearby ruddy Mars will continue to march eastward against the stars, and by the end of the week Venus will approach the golden glow of Saturn.  Capping off the week is the arrival of the slender waning crescent Moon.  Weather permitting, I’ll be outside watching the show.
 
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