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Twice in a Month, or Once in a Blue Moon?

by Geoff Chester, USNO Public Affairs | 23 August 2023

by Geoff Chester, USNO Public Affairs | 23 August 2023

The Full (Worm) Moon, imaged 2023 March 7, 01:59 UT from Alexandria, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor, iOptron AZ Mount Pro
and a ZWO ASI183MC color CMOS imager

We’ll be taking a short late summer vacation until after Labor Day.  Weekly updates will resume at that time.

The Moon waxes in the evening sky, culminating in August’s second Full Moon, which will occur on the 30th at 9:36 pm Eastern Standard Time.  Between now and then, First Quarter falls on the 24th at 5:57 am EDT.  This second Full Moon is one of two types of “Blue Moon”.  

The term applies to either the second full Moon in a calendar month (as we have this year) or the third Full Moon to occur in an astronomical season (i.e. between equinoxes and solstices) that has four Full Moons. This second type of Blue Moon will occur on August 24th next year.  Both of this month’s full Moons also happen to occur close to the times of the Moon’s closest perigees for the year, which some people like to refer to as “Super Moons”.

Look for the Moon close to the bright star Antares on the evening of the 24th.  Here in Washington, Luna will occult the star beginning at 10:54 pm EDT, but she will only be nine degrees above the horizon.  Hope for haze-free skies to observe this event.  Most of the rest of the country west of Washington will see the entire event.  Look for Saturn near the Full Moon on the evening of the 30th.  Late night skywatchers can see the waning gibbous Moon rising near bright Jupiter on the late evenings of the 3rd and 4th.

The waxing Moon will gradually wash out the finer details of the sky as she progresses to her full phase.  For most urban and suburban dwellers, the sky is already affected by artificial lighting, but folks in darker locations will lose sight of the Milky Way and many of the fainter stars that delineate summer’s distinctive constellations.  Fortunately, we have the Moon herself to peruse with binoculars or telescopes as the terminator line slowly advances across her barren, pock-marked face.  I often tell people at star parties that our natural satellite is “looked over, then overlooked” by neophyte telescope owners.  While her features are frozen in time, each lunation brings subtle changes in lighting that highlight her many plains, mountain ranges, and craters that have kept me coming back to explore her for decades.  No other celestial object offers so much variety of detail for owners of small telescopes.

Besides the Moon, there are bright stars that can guide you to other interesting objects to look at.  Overhead at around 10:00 pm you will see the bright stars that form the Summer Triangle asterism.  In the middle of the triangle look for the star Albireo, which marks the “head” of Cygnus, the Swan.  Here you will find one of the easiest double stars to see in a small telescope.  Its components offer a striking color contrast of blue and gold that is best seen with smaller aperture instruments.  It was one of the first double stars that I observed with my first telescope, and I still enjoy viewing it and sharing the sight with others.

If you look at Vega, the brightest star in the Triangle, binoculars will show a close pair of stars just northeast of the bright star.  If you look at the pair with a good 3-inch or larger telescope, you will see that each of the components of the binocular pair is itself a close double star.  Known to amateur astronomers as the “Double-double”, the close pairs are good tests for the quality of small instruments.

Saturn reaches opposition from the Sun on the 27th, when it rises at sunset and sets at sunrise.  For a few weeks, when Jupiter begins to encroach on the early evening hours, Saturn has the limelight for planetary observers.  Saturn lies between two dim constellations, Capricornus and Aquarius, so there isn’t much competition in this part of the sky.  Saturn’s yellow tint makes him an easy target for the telescope, and one’s first view of the planet will often elicit feelings of disbelief.  The rings, however, are very real and offer s sight unique to Saturn among his planetary relatives.

Jupiter rises just before 11:00 pm as the week opens, and by Labor Day comes up shortly after 10:00 pm.  He dominates the eastern sky during the late night and early morning hours and heralds the arrival of the winter constellations.  The best time to view him in the telescope is still just before the onset of morning twilight, when he stands high in the south.


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

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