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Don't Overlook the Moon!

by Geoff Chester, USNO Public Affairs | 27 September 2022

by Geoff Chester, USNO Public Affairs | 27 September 2022

The Moon, 2021 April 20, 01:31 UT, imaged from Alexandria, Virginia
with an explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor

The Moon returns to the evening sky this week, skirting the southern horizon as she waxes and glides eastward against the backdrop of summer’s constellations.  First Quarter occurs on October 2nd at 8:14 pm Eastern Daylight Time.  Look for Luna just over a degree from the bright star Antares in the constellation Scorpius on the evening of September 30th.  On the night of the 2nd you will find her in the middle of the “Teapot” asterism of Sagittarius.  By the week’s end she is drawing a bead on Saturn.

October 1st is International Observe the Moon Night, an evening to share views of our wonderful natural satellite and to appreciate the influence the Moon has on our planet, our lives, and our culture.  Sponsored by NASA, you are encouraged to show the Moon to your neighbors if you have a telescope or participate in activities sponsored by local astronomy clubs, planetariums, and science centers.  Here in the Washington, DC area there will be a free public viewing program at the Smithsonian’s Udvar-Hazy Center in Chantilly, Virginia.  The Northern Virginia Astronomy Club will provide telescopes, or you can bring your own to share lunar views.  I often say that the Moon is “looked over, then overlooked” by budding amateur astronomers, but as our closest neighbor in space it offers an amazing landscape of broad plains, towering mountains, and thousands of impact craters.  These battered features bear mute testimony to the violence that birthed the solar system, and with each passing night new features are slowly revealed as the terminator line dividing darkness from sunlight gradually progresses across Luna’s disc.  It takes many observing sessions to appreciate all of the Moon’s mysteries, and even after more than fifty years of looking at her, I still look forward to her return to grace the evening sky each month.  

In addition to the stark beauty of the Moon’s surface, her impact on daily life is often underappreciated.  Anyone who has lived near or visited ocean shores has experienced the daily cycle of the tides and the astonishing variety of life that exists in the intertidal zones.  Hundreds of animal species rely on the phases of the Moon to establish migration patterns and breeding cycles, and Moon lore is endemic to human agriculture and mythology.  Her cycles are embedded in our timekeeping as months and weeks in our calendars.  Feasts and fasts in the Islamic, Hebrew, and Christian calendars are regulated by her changing phases. Her very existence has made life possible on the Earth by constraining the variation in our planet’s axial tilt, allowing for a moderate climate ideally suited for life to thrive.  
In addition to the attraction of the waxing Moon, this is also a good time to enjoy the stars of the Summer Triangle, which are overhead as evening twilight ends.  The three bright stars, Vega, Altair, and Deneb anchor three of summer’s signature constellations, Lyra, Aquila, and Cygnus, respectively.  Each of these constellations host a variety of treats for the telescope, so enjoy them as the Moon sets.  By the late evening, another geometric figure climbs high in the eastern sky.  Four stars form a large square, delineating part of the constellation of Pegasus, the Winged Horse.

Saturn occupies the area marked by autumn’s dimmer constellations.  His golden glow is almost upstaged by the beacon that is Jupiter, but the ringed planet is still easy to find, even from urban skies.  The planet’s famed ring system is visible through just about any telescope, but telescopes of six inches or more in aperture will show their subtle structure.  Look near the outer edge of the rings for a thin black line that is known as Cassini’s Division.  This is a true gap in the rings that’s about half the Earth’s diameter across.

Jupiter is now the unparalleled king of the night sky.  He is closer to Earth than at any time since 1963, and this week he is as bright as he can possibly get.  It is a great time for owners of smaller telescopes since his apparent disc is just shy of 50 arcseconds across.  A three inch instrument will show his equatorial cloud belts, and each increase in aperture will show more detail in his turbulent atmosphere.  His most famous feature, the Great Red Spot, is well-placed for viewing on the evenings of the 28th and October 3rd.
You will find ruddy Mars drifting eastward among the stars of Taurus, the Bull.  You can see him just above the eastern horizon at local midnight, but your best time to view his rusty surface is still in the hours before dawn.


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

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