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The Night Sky of October

Dr. Wayne Wooten
Professor of Astronomy

For October 2013, the moon is 6 degrees south of Mars on October 1st in the morning sky, and new on October 5th. The waxing crescent moon makes a nice triangle with Mercury and Saturn on the evening of October 6th, if you have a clear western horizon about an hour after sunset. The waxing crescent moon passes just above brilliant Venus on October 8th. It is first quarter on October 11th. It is full and rises at sunset on October 18th; in American Indian tradition, this is the “Hunter’s Moon”. This also means the brightness of the full moon will overwhelm most of the peak of the Orionid Meteor Shower on the morning of October 21st. The waning gibbous moon and Jupiter are close together, rising about midnight on October 25th. The last quarter moon is on October 26th, and thus will be a waning crescent in the morning sky for Halloween this year. It is close to Mars again on the morning of October 29th.

Mercury puts on a nice show in the SW evening sky in October. On October 7 the Moon, Mercury, and Saturn all lie in the same binocular field of view, with Mercury below Saturn but brighter. On October 8th, Mercury passes 5 degrees below Saturn, and reaches greatest eastern elongation on the 9th. It will rapidly retrograde between earth and sun in the next weeks, and like Saturn, be lost in the sun’s glare by midmonth. Venus dominates the evening sky for the next several months. She is closing in on earth, getting bigger in our telescopes but less sunlit in phase. As the month begins, it is 62% sunlit and 19” across and shines at magnitude -4.2, bright enough to spot in broad daylight. By Halloween, she is exactly half lit, at greatest eastern elongation, but now up to 25” across, and even brighter, at magnitude -4.4, very close to her brightest appearance.

Mars is faint in the dawn sky, on the far side of his orbit. A year from now at opposition, he will be much closer and brighter. Jupiter dominates the later eastern sky and sits in the middle of Gemini, rising about 9:30 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, and should be visible at 100X in telescopes 3” or larger in aperture.

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. Just SE of the southern wing of Cygnus (epsilon Cygni) is the location of the very photogenic Veil Nebula, the remains of a supernova that exploded perhaps 8,000 years ago, probably lighting the earth’s skies brighter than Venus appears now. The “funeral wreath” for this star now stretches across 3 degrees of sky, and is visible with big binoculars. Our featured photo for October is taken with a 4” refractor by EAAA member Eric King, and shows the shattered star expanding outward . 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.

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 pair of giant stars the same temperature as our sun, but at least 100X more luminous and about 10X larger than our sun. It lies about 43 light years distant. A little farther south, below the Pleiades, orange Aldebaran rises. It is the eye of Taurus the bull, with the V shaped Hyades star cluster around it making the head of the bull. This colorful giant star is only 2/3 as hot as our yellow sun, but 44X times larger and at 65 light years distant, one of the closest of these monster stars.

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