The Night Sky of October

Dr. Wayne Wooten
Professor of Astronomy

For October 2011, the moon is first quarter on October 4th. The moon will be full on October 12th; this full moon is the Hunter’s Moon. The waning gibbous moon, just past full, passes five degrees north of Jupiter on October 13th. The last quarter moon rises at midnight on October 20th. The waning crescent moon passes six degrees below Mars on the morning of September 21st, the same morning as the peak for the Orionid Meteor Shower. New Moon is on October 26th, and the slender crescent moon lies just east of Mercury and Venus in the SW twilight on October 28th. Halloween will see a slender crescent moon in the SW evening twilight, while Jupiter at its brightest dominates the eastern sky for trick or treaters, rising in the east at sunset.

Venus returns to the evening sky at the end of this month, having past behind the sun in the last few weeks. It is briefly joined by Mercury for a few days in late October and early November. While Mercury quickly passes between us and the Sun in mid November, Venus will be pulling away from the Sun, appearing higher and brighter in the evening sky for the next six months. But Venus reaches the edge of her orbit as seen from Earth next May, and then quickly retrogrades between us and the Sun, to transit the sun as a black dot in front of our star. This will next happen on the late evening of June 5, 2012, which is what got all the Mayan 2012 hype started as their Venus based calendar resets, very similar and just as ominous as our own Y2K a decade ago.

Jupiter dominates the eastern sky just below the triangle of Aries and south of Andromeda. 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 cloudmark.

Mars lies in Gemini in the morning sky, far from the earth and quite faint. Saturn is totally invisible, passing behind the Sun on October 13th, but returning to the morning dawn sky in November.

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, and are plotted on the sky map for the month.

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. Our fine image this month is of the closest galaxy comparable to our own Milky Way. Note its two smaller companions, M-32 and M-110.

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.

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