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Pursuing the Hunter's Moon

Oct. 4, 2022 | By Geoff Chester, USNO Public Affairs

Collinder 399, the "Coathanger" cluster, imaged 2016 August 18 at Great Meadow, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel T2I DSLR.
The distant galactic cluster NGC 6802 lies just to the east (left).

The Moon brightens the crisp autumn evenings as she skirts the southern horizon this week.  Full Moon occurs on the 9th at 4:55 pm Eastern Daylight Time.  October’s Full Moon is popularly known as the Hunter’s Moon.  Other names include the Falling Leaves Moon and Freezing Moon.  Look for Luna five degrees southeast of Saturn on the evening of the 5th.  She lies just three degrees from bright Jupiter on the evening of the 8th.

The circumstances that gave us the Harvest Moon in September largely repeat themselves this month, yielding relatively short intervals in successive moonrises around the time of Full Moon.  Here in the Washington area the Moon rises just 25 minutes later on these nights.  In northern European traditions, this gave hunters a bit of extra light at the end of the day, allowing them to have some extra time to pursue game across the stubble of the previous month’s harvested fields.  This tradition, like many others in popular skylore, are quite “boreocentric”, derived from cultures that thrived in the Northern Hemisphere.  Our Southern Hemisphere friends see a mirror image of our seasons, so their versions of the Harvest and Hunter’s Moons occur in March and April.

The bright Moon washes out the fainter constellations of the autumn sky, but we still have a number of bright targets that we can enjoy at night.  The stars of the Summer Triangle asterism may be found overhead at the end of evening twilight, and each of their respective constellations have objects that defy the Moon’s silvery glow.  If you use binoculars, look at the area near the Triangle’s brightest star Vega.  Just to the northeast of the star you will see a close pair of fainter stars known as Epsilon Lyrae.  Point a small telescope toward this pair and you will discover that each of the components of the wide pair are also double stars with very close separations.  Resolving these two pairs is considered to be a good test of the capabilities of a three-inch aperture telescope.  The four stars share a common motion through space and are located about 160 light-years away, suggesting that Epsilon Lyrae is a true quadruple star system.  

A much easier and more colorful double star is located almost in the center of the Summer Triangle.  Your unaided eye will show a single third magnitude star that easily splits in a small telescope.  This star, known as Albireo, splits into yellow and blue components that show a beautiful color contrast.  There is some debate as to whether they represent a true binary pair or are an “optical double” that happen to lie along the same line of sight.  The brighter yellow component has been shown to be a very close binary system.

Our final bright sky target is easily located in binoculars just west of a line between Albireo and the bright star Altair, southernmost star in the Summer Triangle.  You should see a short, straight line of stars with a small “loop” hanging midway along the line.  It resembles an upside down coathanger, which gives it its popular name of the “Coathanger Cluster”.  First described by the 10th Century Persian astronomer Al Sufi, it can be detected by keen-eyed people under dark skies.  It has been “discovered” by generations of neophyte amateur astronomers and forms a striking asterism for those who stumble upon it for the first time.

Saturn crosses the meridian at around 9:30 local time.  This is when the ringed planet reaches his highest elevation for northern hemisphere observers.  Here in Washington this places Saturn just under 35 degrees above the horizon.  The hour before and after the planet’s meridian transit offer the best time to view him through the least amount of Earth’s atmosphere.  For most of us that’s “prime time”.

Jupiter beams down from a perch high in the southeastern sky.  Old Jove appears shortly after sunset and dominates the night sky until the beginning of morning twilight.  He is still at his peak brightness for the current opposition, and his generous apparent disc means that owners of smaller telescopes should get a good view of his complex, turbulent atmosphere.

Ruddy Mars is steadily brightening as he drifts along the northern reaches of the ecliptic.  He crosses the meridian at around 5:30 am local time and outshines his nearby stellar rivals Aldebaran and Betelgeuse.  His eastward motion is slowing as he prepares to put on a fine evening show in December.  Modest-aperture telescopes should be able to reveal some of his dusky surface features.
 
Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529