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The Night Sky of October

Dr. Wayne Wooten
Professor of Astronomy

For October 2018, the moon is last quarter on October 2nd, rising at midnight. The new moon is on October 8th. Right after sunset on October 9th, try to catch a neat string of the crescent moon, Mercury, and rapidly disappearing Venus along the SW horizon; binocs will help for Mercury. The waxing crescent passes north of Jupiter on October 11th, and then close to Saturn on October 14th. First quarter moon is October 16th, and the waxing gibbous moon passes north of Mars on October 18th. The full moon, the Hunter’s Moon, in October 24th, but Halloween this year will feature a waning gibbous moon rising about midnight, a little late to treat young stargazers to, alas.

We can see all five naked eye planets in the evening sky early in October, but look fast! Mercury starts appearing low in SW about October 10th, and is just 3.2 degrees south of much brighter Jupiter on October 28th. But the real show is the dramatic changes in Venus’s size and phase, as it rapidly passes six degrees south of the Sun into the morning sky on October 26th. As October begins, look for Venus is twilight in SW as a 16% lit crescent, the phase easily noted in hand held binoculars! As she retrogrades between us and the Sun, the planet grows larger, but becomes a thinner crescent daily. Our featured shot for this month is by EAAA member Gary Wiseman, which shows how the slender crescent will appear in a scope about October 10th in the daytime sky; catching it in the evening will get harder and harder daily, and by month’s end, it rises before the Sun in the dawn!

Jupiter in Libra is also getting lost in the sun’s glare in the SW twilight, but does have that neat conjunction with Mercury at month’s end. It will be lost in sun’s glare in November. Saturn is still out in Sagittarius in the SW, but also will be gone by Christmas. Even Mars is fading in the SE in Capricornus, but it will remain in the evening sky well into 2019.

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. Saturn lies above of the pour spout now. 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 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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