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The Night Sky of October

Dr. Wayne Wooten
Professor of Astronomy

For October 2017, the moon is full, the Hunterís Moon, rises at sunset on October 5th. The last quarter moon is on October 12th. The waning crescent moon passes north of brilliant Venus and much fainter Mars on the morning of October 17th. The new moon on October 19th will not interfere with the peak for the Orionid Meteor Shower on the morning of October 20th. This is debris from Comet Halley, and about a meteor every 3-4 minutes seem to come out of Orionís head were the skies dark enough. The waxing crescent moon passes 3 degrees north of Saturn in twilight on October 24th. First quarter moon is October 27th, and Halloween this year will feature a waxing gibbous moon for amateur astronomers to treat the young visitors to.

Saturn, the only evening planet this month, is getting lower in the western sky daily after sunset, and will be lost in the Sunís glare by late November. The action is before sunrise, with brilliant Venus passing only .2 degrees north of fainter red Mars on the morning of October 5th. Jupiter is lost in the sunís glare all month, but will emerge into the dawn sky in November.

While the naked eye, dark adapted by several minutes away from any bright lights, is a wonderful instrument to stare up into deep space, far beyond our own Milky Way, binoculars are better for spotting specific deep sky objects. For a detailed map of northern hemisphere skies, about September 30th visit the www.skymaps.com website and download the map for October 2017; it will have a more extensive calendar, and list of best objects for the naked eyes, binoculars, and scopes on the back of the map. Also available as the next month begins is wonderful video exploring the October 2017 sky, available from the Hubble Space Telescope website at: http://hubblesite.org/explore_astronomy/tonights_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 monthís end. East of the Scorpionís tail is the teapot shape of Sagittarius, which marks the heart of our Milky Way galaxy. Saturn lies just west of the pour spout now. Looking like a cloud of steam coming out of the teapotís 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 Pegasusíí 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 feature photo is of this galaxy by Rick Johnston, and shows it with its two smaller companion galaxies, M-32 and M-110. This is about how the galaxies appear in large amateur scopes.

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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