The Night Sky of October

Dr. Wayne Wooten
Professor of Astronomy

For October 2012, the moon was full on September 30th. The waning gibbous moon, just past full, passes one degrees south of Jupiter on October 5th. The last quarter moon rises at midnight on October 8th. The waning crescent moon passes six degrees below Venus on the morning of October 12st. The New Moon is on October 15th, and the slender crescent moon lies just east of Mercury in the SW twilight on October 17th. The waxing crescent moon passes 2 degrees above red Mars on October 18th. The first quarter moon is on October 22, and will not be a problem for observing the peak of the Orionid Meteor Shower on the morning of October 21st. The Full Moon, the Hunter’s Moon, is on October 29th. Halloween will see a waning gibbous moon rising in the SE in evening twilight, a big orange pumpkin moon rising locally about 7:30 PM, and bright Jupiter rising just below it at 8 PM. Get out the telescope and give the youngsters in the neighborhood a cosmic treat.

Mercury puts on a nice show in the SW evening sky in October. On October 1st, it lies 1.6 degrees north of Spica in the SW, then on the 5th, it passes 3 degrees below Saturn. This is our last view of Saturn for several weeks, as it will lie behind the Sun for the rest of October, returning to the morning sky in late November. Mercury’s greatest elongation is on October 26th, so it lies low in the evening sky for the whole month, with the crescent moon just below it on October 17th. Mars races the sun eastward in October, moving through Scorpius, and making a neat pair with similarly red Antares on October 21st . Jupiter dominates the eastern sky and sits in the horns of Taurus the Bull, rising about 7 PM by month’s end.

Any small scope will reveal what Galileo marveled at 400 years ago; four large moons, all bigger or similar to ours in size, orbit it in a line along Jupiter’s equator. So get out the old scope, and focus on Jupiter for a constantly changing dance of the moons around the giant world. Bigger scopes real much detail in its clouds, which have now returned to their familiar two racing stripes. For over a year, the south equatorial belt faded, but has now returned to its normal prominence. Its famed Great Red Spot is still its most distinctive cloud mark. Astronomers got a neat surprise in early September when an asteroid hit Jupiter’s cloud tops, with a bright flash captured by two amateur astronomers. Unlike the Comet SL-9 impacts in July 1994, this smaller impact left no dark smoke marks in Jupiter’s atmosphere, however. Venus dominates the dawn, but is moving behind the Sun so appears smaller and fainter and closer to the sun each morning. At the beginning of October, it is rising about 3:30 AM, but by month’s end, an hour later and much lower in sky.

The Big Dipper falls lower each evening. By the end of October, it will be only the three stars in the handle of Dipper still visible in the northwestern twilight. By contrast, the Little Dipper, while much fainter, is always above our northern horizon here along the Gulf Coast.

To the southwest, Antares and Scorpius also set soon after twilight, and will be gone by month’s end. 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. This stellar nursery is ablaze with new stars and steamers of gas and dust blown about in their energetic births. In the same binocular field just north of the Lagoon is M-20, the Trifid Nebula. Many other clusters visible in binoculars as you sweep northward along the Milky Way.

The brightest star of the northern hemisphere, Vega dominates the sky overhead. To the northeast of Vega is Deneb, the brightest star of Cygnus the Swan. 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 autumn evenings. To the east of Altair lies tiny Delphinus, a rare case of a constellation that does look like its namesake. In the sky myths, our dolphin saves the Greek poet Arion of Lesbos. He was a court musician at the palace of Periander, ruler of Corinth. Arion had become famous and rich during his travels to Sicily and Italy. On his way home his wealth caused the crew of his ship to conspire against him. Threatened with death, Arion asked to sing a dirge. As he sang, he threw himself overboard. He was rescued by a dolphin which had been charmed by Arion's music. The dolphin carried Arion to the coast of Greece and left, to be celebrated by Arion and others in the sky. Many maritime people loved the dolphins, particularly the Minoans, who have leaping dolphins on many walls of the Knossos palace. Can you see him overhead under clear, dark skies in October?

To the east, the square of Pegasus is a beacon of fall. South of it lies the only bright star of Fall, Fomalhaut. If the southern skies of Fall look sparse, it is because we are looking away from our Galaxy into the depths of intergalactic space. The constellation Cassiopeia makes a striking W, rising in the NE as the Big Dipper sets in the NW. Polaris lies about midway between them. She contains many nice star clusters for binocular users in her outer arm of our Milky Way, extending to the NE now.

Her daughter, Andromeda, starts with the NE corner star of Pegasus’’ Square, and goes NE with two more bright stars in a row. It is from the middle star, beta Andromeda, that we proceed about a quarter the way to the top star in the W of Cassiopeia, and look for a faint blur with the naked eye. M-31, the Andromeda Galaxy, is the most distant object visible with the naked eye, lying about 2.5 million light years distant. It is a bigger version of our own Galaxy, which it may collide with about three billion years from now.

Below Andromeda is her hero, Perseus. In his hand is a star most appropriate for Halloween, Algol. This star "winks" at us for six out of every 70 hours, which Arabic astronomers centuries ago found spooky, hence naming it "the ghoul" . We know today it is an eclipsing binary system, with the larger, cooler orange star covering 80% of its smaller, hotter neighbor during the "wink". At the foot of Perseus, the hero of "Clash of the Titans" is the fine Pleiades star cluster, the "seven sisters" that reveal hundreds of cluster members in large binoculars. This might be the best object in the sky for binocular users.

Winter will be coming soon, and in the NE we see yellow Capella rising. It is the brightest star of Auriga the Charioteer, and a giant star the same temperature as our sun, but at least 100X more luminous. A little farther south, below the Pleiades, orange Aldeberan rises. It is the eye of Taurus the bull, with the V shaped Hyades star cluster around it making the head of the bull. Jupiter lies just east of Aldeberan, in the middle of the Bull’s horns this month, but retrogrades back westward toward Aldeberan by the end of the month.

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