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

Celebrate and Explore the Dark Sky!

by Geoff Chester, USNO Public Affairs
19 April 2022

Messier 101, the "Pinwheel Galaxy" in Ursa Major, imaged 2022 March 26 from Mollusk, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a ZWO ASI183MC CMOS imager. North is to the left.
M101 is located about 21 million light years from Earth.

The Moon wends her way through the southern reaches Globe aof the ecliptic this week, skirting the horizon as she passes through the rising summer constellations.  Last Quarter occurs on the 23rd at 8:56 am Eastern Daylight Time.  You will find Luna in the pre-dawn sky above the stars that form the “spout” of the “Teapot” asterism in Sagittarius on the 21st.  By the week’s end she sidles up to the string of planets that announce the coming of dawn. 

The April observing campaign for the citizen-science Globe at Night program begins on the 22nd.  This is also the start of International Dark Sky Week (IDSW), a worldwide effort sponsored by the International Dark Sky Association to raise awareness of the threat that artificial nighttime lighting poses, not only to our view of the stars, but to our physical health and the health of the planet itself.  “Light pollution” not only robs us of the experience of the spectacle of the night sky, it also contributes to changes in global climate and ecosystems.  The unwanted light that we put into the sky costs us over $7 billion a year and pumps over 20 million tons of carbon dioxide into the atmosphere annually.  The goal of IDSW is to make more people aware of the issue of light pollution and to promote strategies that will lower the output of wasted light with reasonable and achievable actions. 

To participate in the Globe at Night program, go to their website and follow their directions to locate the constellation of Leo, the Lion.  Compare your view of Leo with the charts on the site’s web app reporting form and record your findings.  For IDSW, contact your local amateur astronomy club to participate in their events for the week.  Here in the Washington, DC area free stargazing events will be held on the 22nd and 30th at Sky Meadows State Park near Paris, Virginia and on the 23rd at the Smithsonian’s Udvar-Hazy Center in Chantilly, Virginia and at Great Meadow near The Plains, Virginia.

Some of the sights you are able to see at these IDSW events range from relatively nearby targets to galaxies that lie millions of light years away.  The spring sky offers only a few bright stars, but among these are a couple of distinctive constellations.  High in the north you will find the asterism known as the “Big Dipper” formed by the seven brightest stars in the constellation of Ursa Major, the Great Bear.  High in the south is the distinctive outline of Leo, the target constellation for the Globe at Night campaign.  Rising in the east is Arcturus, the lead star in the constellation of Bo├Âtes, the Herdsman.  Each of these constellations host beautiful double stars.  Mizar is located at the “bend” in the “handle” of the Big Dipper and is easy to split in small telescopes.  In Leo, the second-magnitude star Algieba lies just north of Regulus, Leo’s brightest star.  It resolves into a pair of golden suns.  Izar is a close pair of yellow and blue stars that lie 10 degrees northeast of Arcturus.  Behind these constellations lies the “Realm of the Nebulae”, where modest aperture telescopes will reveal dozens of faint smudges of light, each representing distant external galaxies that are part of a huge cluster that includes our own Milky Way.  While the distances to the double stars range out to two hundred light years, the distances to the galaxies are far greater.  When their wispy glimmers waft through the telescope eyepiece, you are looking across a gulf of space and time spanning tens of millions of light years!

The bright planets are now stretched out in a line in the pre-dawn sky.  From west to east you will find Saturn, Mars, Venus, and Jupiter.  The highlight for this week is the closing pair of dazzling Venus and bright Jupiter, which should be easy to spot low in the southeast about 45 minutes before sunrise.  By the week’s end Venus will be just three degrees west of Old Jove.  By the end of the month they will be less than half a degree apart.  On the morning of the 27th the waning crescent Moon joins the bright planets in the gathering twilight.
 
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