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The Night Sky of September

Dr. Wayne Wooten
Professor of Astronomy

For September 2017, the moon will be full on September 6th, this is the Harvest Moon. The moon is last quarter on September 13th, and the waning crescent Moon passes Venus in the dawn on September 17th. The new moon is September 20th, but no more solar eclipses for us locally until 2023! The Moon is first quarter on September 28th, close to Saturn in the evening sky.

To the west, Jupiter is briefly visible in evening twilight at month’s start, near the bright star Spica in Virgo. At dusk, Saturn lies north of the stinger tail of Scorpius, and its rings are tilted wide open for great telescopic views now. Venus is heading back toward the Sun in the dawn, and Mercury and Mars are also too close to the sun for easy viewing now.

The Big Dipper rides high in the NW at sunset, but falls lower each evening. Good scouts know to take its leading pointers north to Polaris, the famed Pole Star. For us, it sits 30 degrees (our latitude) high in the north, while the rotating earth beneath makes all the other celestial bodies spin around it from east to west. It is this time of year at an American Indian legend tells of the Bear and three hunters. The bowl is the bear, the three handle stars of the dipper the hunters. The first carries a bow, and has shot the bear in its flanks. The second optimistically carries a bowl on his shoulder for bear stew; look closely, and you can see the pot (Mizar, horse in Arabic, and Alcor its rider more traditionally). The last hunter carries firewood for the feast. The wound is minor, and the bear has not lost a step, but in the fall, as the bear goes into hiding along the NW horizon, the wound opens slightly, and blood oozes out to fall on the tree leaves and paint them red this time of year.

From the Dipper’s handle, we "arc" SE to bright orange Arcturus, the brightest star of Spring. Spike south to Spica, the hot blue star in Virgo. Jupiter is just NW of Spica, a little brighter and more yellow in color. Note that Spica is now low in the SW, and by September’s end, will be lost in the Sun’s glare due to our annual revolution of the Sun making it appear to move one degree per day eastward. To the Greeks, Spica and Virgo were associated with Persephone, the daughter of Ceres, goddess of the harvest. In their version of "Judge Judy", the beautiful young daughter falls for the gruff, dark god of the underworld, Pluto. He elopes with her, much to the disapproval of mother Ceres, and they marry in his underworld kingdom of Hades…a honeymoon in hell…really, he does love her as well, and the marriage itself works well. But it is the reaction of Ceres that creates alarm.

Very despondent over the loss of her young daughter to a fate as bad as death, Ceres abandons the crops, which wither. Soon famine sets in, and humanity appeals to Jupiter to save us all. Calling all together, Jupiter hears that Ceres wants the marriage annulled, Persephone loves them both, and Pluto wants his mother in law to stop meddling. Solomon style, Jupiter decides to split her up, not literally, but in terms of time. In the compromise (aren’t all marriages so?), when you can see Spica rising in the east in March, it means to plant your peas. For the next six months, she visits upstairs with as very happy mama, and the crops will prosper. But now, as Spica heads west (to the kingdom of death, in most ancient legends) for six months of conjugal bliss with Pluto, it is time to get your corn in the crib. This simple story, told in some form for as long as Noah’s flood, was one of the ways our ancestors 7,000 years ago knew the solar calendar and when to plant and harvest. As you watch Spica fade, thank this star for agriculture, and in a certain sense, even our own culture.

 

To the south, Antares marks the heart of Scorpius. It appears reddish (its Greek name means rival of Ares or Mars to the Romans) because it is half as hot as our yellow Sun; it is bright because it is a bloated red supergiant, big enough to swallow up our solar system all the way out to Saturn’s orbit! Saturn sits about 6 degrees north of Antares this fall. Near the tail of the Scorpion are two fine open clusters, faintly visible to the naked eye, and spectacular in binoculars. The clusters lie to the upper left of the bright double star that marks the stinger in the Scorpion’s tail. The brighter, M-7, is also known as Ptolemy’s Cluster, since he included it in his star catalog about 200 AD.

East of the Scorpion’s tail is the teapot shape of Sagittarius, which marks the heart of our Milky Way galaxy. Looking like a cloud of steam coming out of the teapot’s spout is the fine Lagoon Nebula, M-8, easily visible with the naked eye. Many other clusters and nebulae lie toward the galactic center, and are shown on the SkyMap chart and discussed on its binocular and telescope object listing on page 2.

The brightest star of the northern hemisphere, Vega dominates the NE sky. Binoculars reveal the small star just to the NE of Vega, epsilon Lyrae, as a nice double. Larger telescopes at 150X reveal each of this pair is another close double, hence its nickname, "The Double Double". This is fine sight under steady seeing conditions over 150X with scopes 4" or larger. Our featured object of the month lies at the other end of the parallelogram of Lyra, Between the two bottom stars; the Ring Nebula, marked "M-57" on the Skymap, is a smoke ring of gas and dust expelled by a dying red giant star while its core collapsed to a white dwarf. A similar fate is expected for our own sun in perhaps five billion more years.

To the northeast of Vega is Deneb, the brightest star of Cygnus the Swan. At the other end of the "northern Cross" that makes up the body of Cygnus is Alberio, the finest and most colorful double star in the sky. Its orange and blue members are well resolved at 20X by any small scope. To the south is Altair, the brightest star of Aquila the Eagle, the third member of the three bright stars that make the Summer Triangle so obvious in the NE these clear September evenings.

Read past issues of the Sky at Night