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No Rest for the Weary?

by Geoff Chester, USNO Public Affairs | 23 May 2023

by Geoff Chester, USNO Public Affairs | 23 May 2023

The Smoky Moon (with Earthshine), 2023 May 23, 01:27 UT
Imaged from Alexandria, Virginia through smoke from Canadian wildfires
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel SL2 DSLR.

The Moon waxes in the evening sky this week, beginning with a fine grouping with the planets Venus and Mars, then turning southward to cruise through the spring constellations.  First Quarter occurs on the 27th at 11:22 am Eastern Daylight Time.  Look for the Moon to pass between the stars Regulus and Algieba in the “Sickle” asterism of Leo, the Lion on the evening of the 26th.  Luna ends the week just west of the bright star Spica in the constellation of Virgo.

It is now the time of year that many amateur astronomers hate.  From now until July 20 the duration of daylight at Washington’s latitude is over 14 hours 30 minutes.  When you factor un the times of astronomical twilight we have just six hours of complete darkness, and thanks to the observance of Daylight Time the sky isn’t completely dark until after 10:15 pm.  For many of us who enjoy a dark night sky, staying up until the wee hours is a necessary evil, and we learn to do our best to come to grips with sleep deprivation.  However, the twilight hours are some of the best times to look at our nearest neighbor in space, the Moon.  I often start my lunar observing sessions right after sunset.  The contrast with the darkening sky allows the eye to gradually adapt to the brightness of the Moon’s surface, and during the crescent phases the ghostly light of Earthshine becomes more apparent as the sky changes from deep blue to back.  As Luna’s phase increases, new landscapes gradually come into view.  This week the sunrise terminator moves over several of the Moon’s more prominent “seas”.  One of the smaller but more prominent ones is the Mare Crisium, the “Sea of Crises”, which is visible to the unaided eye.  It is the only lunar “sea” that is isolated from the rest of the Mare formations on the Moon’s near side, and was formed by the impact of an asteroid some 3.85 billion years ago.  Its surface is quite smooth, but several small craters are scattered along its western edge.  Many of these are named for 19th Century astronomers or the benefactors of classical observatories.  Another small “sea” will be well-placed on the evening of the 25th. Mare Nectaris, the “Sea of Nectar”, has two very prominent craters on its western edge.  Theophilus is the most striking with its central peak and the incursion of its rim over the equally large crater Cyrillus.  Both craters are about 100 kilometers (62 miles) in diameter, and although Theophilus looks quite “fresh”, it formed well over one billion years ago.

The end of evening astronomical twilight brings the spring constellations into view.  This is the best time of the year to look for the “Big Dipper” asterism of the constellation Ursa Major, the Great Bear.  You will find the Dipper high in the northern part of the sky, which gives it an upside-down appearance.  If you follow the curve of the Dipper’s “handle”, you will easily spot the bright glow of the bright star Arcturus.  An easy way to remember this is to “follow the arc to Arcturus”.  The brightest star in the northern half of the sky, Arcturus is part of the constellation Boötes, the Herdsman.  While the Dipper resembles its namesake, the Herdsman requires a good sky as well as a good stretch of imagination.  I can trace out something resembling a kite or an ice cream cone from a dark sky site, but urban dwellers will be hard-pressed to see more than a few scattered stars.  However, once you have followed the arc to Arcturus, continue southward to “speed on to Spica”, the brightest star in the sprawling constellation of Virgo.  This is another pattern that requires dark skies to trace out, and the figure reminds me of a bent martini glass.  For the urban stargazer, compare the colors of Arcturus and Spica.  The blue tint of Spica indicates that its surface is very hot while the rosy tint of Arcturus indicates that it is comparatively cooler.  Spica is actually a very close binary system with a period of just over four days that’s located some 250 light-years away.  To appear as bright as it does in our sky, the Spica system must shine about 25,000 times brighter than our Sun!

Early risers can welcome more bright stars that will be more prominent in the later summer skies.  The bright stars Vega, Altair, and Deneb, collectively known as the Summer Triangle, give us a hint of the bright constellations to come.

Venus continues to trek through the stars of Gemini, and by the week’s end she will pass the Twin Stars Castor and Pollux.  She gets a visit from the Moon on the evening of the 23rd, setting up a good photo opportunity  during the evening twilight hours.

Ruddy Mars spends the week among the dim stars of Cancer, the Crab.  He entertains the waxing Moon on the evening of the 24th, then spends the rest of the week closing in on the binocular star cluster known as The Beehive.  He will pass through the cluster on June 1st and 2nd.

Golden Saturn rises shortly after 2:00 am local time and is quite prominent in the southeast as morning twilight gathers.


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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