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The Night Sky of October

Dr. Wayne Wooten
Professor of Astronomy

For October 2010, last quarter moon is October 1st . New Moon is on October 7th. The waxing crescent moon passes 3.4 degrees north of brilliant Venus in SW twilight on October 9th. The moon is first quarter on October 14th, and the waxing gibbous moon passes 6 degrees north of bright Jupiter in the SE on October 20th. As Jupiter is very close and bright now, try finding both of them just before sunset with the naked eye. It is challenging, but Jupiter may be bright enough to spot, using the moon as your guide. The moon will be full on October 23rd, which means the peak for the Orionid Meteor shower will be lost in its glare on the morning of October 21st. Halloween finds the moon at last quarter on the 30th, not rising until midnight, a little late for trick or treaters.

Venus dominates the evening sky as October begins, but rapidly retrogrades between us and the Sun this month. It is at inferior conjunction on October 29th, and by Halloween rises just before the Sun in the morning sky. On October 1, Venus is near greatest brilliancy, mag. -4.56, with a slender crescent 18% sunlit and a disk 45" of arc across, easily seen in hand held binoculars. By the 15th, Venus has moved closer to the Sun, is lower in the western twilight, and faded to mag. -4.4, with a even closer and larger disk now 55" of arc wide, but very slender crescent, only 6% still sunlit.

While Venus passes below the Sun’s disk this October 29th, it does occasionally transit the Sun’s face, appearing as a black dot in front of our star. This will next happen on June 5, 2012, which is what got all the Mayan 2012 hype started as their Venus based calendar resets, very similar as just as ominous as our own Y2K a decade ago. Not to worry…

Jupiter dominates the eastern sky just above the Circlet of Pisces. 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 changed dramatically this part April, when its familiar South Equatorial Belt vanished, leaving Jupiter with only one "racing stripe", the NEB. Its famed Great Red Spot is even more apparent, since the SEB has faded and it is surrounded by a bright white zone now.

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.

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, 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.

Read past issues of the Sky at Night