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29 Sep 2017

October Astronomy: The Timing of the Moon's Cycle Means Great Viewing of a Meteor Shower That Comes From Halley's Comet

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Rise early on these dark mornings, and you will be rewarded by a close planet pair, lots of bright stars, a star popping out from behind the moon, a meteor shower from Halley’s Comet, and a dust cloud in our solar system.

Evenings give us Saturn with rings now open to the max, and the Milky Way.

Our morning twilight all-sky chart for October 2017 at CVIndependent.com shows the changes in positions of naked-eye planets and stars of first magnitude or brighter at mid-twilight, when the sun is 9 degrees below the eastern horizon, some 40 minutes before sunrise. A bonus in October, while we’re still on daylight saving time: You don’t need to get up extra early by the clock to enjoy dark morning skies!

As the month progresses, stars will appear to drift from east to west along the tracks shown, owing to the revolution of Earth around the sun. Venus, of magnitude -4, still dominates the predawn sky. The chart shows Venus getting a little lower in the east each morning, because this swift inner planet is moving farther ahead of Earth and heading toward the far side of the sun, where it will arrive in January 2018, before emerging into the western evening sky.

Mars on Oct. 1 is only 2.5 degrees below Venus. The red planet now glows dimly at magnitude +1.8, as faint as it ever gets. But it plies its orbit more slowly than Earth, so we’ll gain on it, and it will appear higher each morning, passing only 0.2 degrees from Venus on Oct. 5, and climbing 16 degrees to Venus’ upper right by month’s end. Eventually, in late July 2018, Mars will appear low in the southwest at dawn (and in the southeast at dusk). The planet will then be at its closest to Earth since 2003, and up nearly all night, shining at magnitude -2.8.

Annually in October, the huge Winter Hexagon—in clockwise order from its brightest member, Sirius, Procyon, Pollux and Castor, Capella, Aldebaran and Rigel, with Betelgeuse inside—is well placed high in the sky before dawn. The flashing blue-white Dog Star Sirius is its most prominent and southernmost member. Sirius is the brightest star in Earth’s night skies, but it is much less bright than Venus. Capella, north or northwest of overhead, is the Hexagon’s second-brightest and northernmost member. Orion’s three-star belt (not shown) points to the lower left toward Sirius, and to the upper right toward Aldebaran, eye of Taurus, the Bull. Earlier, in darker skies, continue 14 degrees beyond Aldebaran to the striking Pleiades star cluster, beautiful in binoculars!

Far below the Hexagon is the second-brightest star in the heavens, Canopus. It reaches its high point just 4 degrees above the horizon due south at 5:30 a.m. on Oct. 16, near the start of morning twilight. But Canopus may not appear very bright, because much of its luster is lost during the last few miles of its beam of starlight coming in at a low angle through our atmosphere. Pick a very clear morning, and a place where mountains don’t block your view. I have seen this star from Palm Springs, looking through Palm Canyon in the Santa Rosa Mountains to my south. This far southern star reaches its high point 4 minutes earlier each day, 21 minutes before Sirius does, and 36 degrees lower.

Late in October, begin looking for bright, golden Arcturus rising in the east-northeast, and in the last couple of mornings, using binoculars, try for Spica in the same field as Venus. On Nov. 2, Spica will appear just 3.5 degrees to the lower right of Venus.

Morning moon wanderings: If you observe daily one hour before sunrise, then you’ll first spot the moon on Oct. 5, full and low in the west. Climbing steeply upward through the zodiac constellations day by day, the moon will appear 3-4 degrees to the lower right of Aldebaranon Oct. 9. Look through binoculars, and you may see several stars of the Hyades cluster, marking the face of Taurus, the Bull. On the next morning, find the moon 11 degrees to the upper left of Aldebaran.

The moon appears 11 degrees from Betelgeuse, Orion’s shoulder, on Oct. 10 and 11. On Oct. 12, the last quarter moon—half full and 90 degrees, or one-quarter circle, away from the sun—appears 10 degrees from Pollux, the brighter of the Gemini Twins, and 14 degrees from Procyon, the Lesser Dog Star. Look for Castor, the fainter Twin (not shown on the map), just 4.5 degrees north of Pollux.

Go outside shortly after 3 a.m. on Sunday morning, Oct. 15. When the 19 percent crescent moon rises at about 2:44 a.m., the star Regulus, heart of Leo, the Lion, will be hidden behind it! As the moon rises higher, the star will remain hidden for another half hour, until at 3:13 a.m., telescopes will show the star suddenly emerging at the dimly Earth-lit upper edge of the moon, then only 5 degrees above the horizon, and 11 degrees north of due east. By 5:30 a.m., the moon’s dim edge will be more than two-moon-widths from the star!

On Tuesday, Oct. 17, face east an hour before sunup to find a 5 percent crescent moon, with Venus 5-6 degrees below, and Mars 2 degrees to the upper right. On the next, final morning, Oct. 18, find the 2 percent, old crescent moon, 30 hours before new, 6-7 degrees to the lower left of Venus. The new moon, invisible in conjunction with the sun, occurs on Oct. 19 at 12:12 p.m. The morning sky thus becomes moonless, ideal for viewing the Orionid meteor shower at its best, in the dark predawn hours of Oct. 20-22. Orionids are dust particles originating from Halley’s Comet and might light up anywhere in the sky. Confirm a suspect meteor’s identity by extending its path backward past the start of its light-streak to a common origin, called the radiant. The true Orionids will appear to race away from the radiant in Orion’s club, north of Betelgeuse.

Another phenomenon excellent from very dark locations this time of year is the Zodiacal Light, reflected from comet and asteroid dust in the inner solar system. The best dates in the remainder of 2017 are Oct. 1, 2, Oct. 18-Nov. 1, and Nov. 17-30, about 90 minutes before sunrise. Look for a huge diffuse cone of light, broad near its base with its main axis near the ecliptic (marked by Regulus, the Beehive Cluster, Mars and Spica, after that star begins rising before morning twilight in November). Anza Borrego Desert State Park and Borrego Springs are fine places to observe the Zodiacal Light before dawn and the Milky Way after nightfall. This year, Oct. 19-22 would be an especially good time to visit; check out nightfallstarparty.com.

Our all-sky evening twilight chart for October shows the Summer Triangle of Vega, Altair and Deneb overhead, with Arcturus sinking low in the west to west-northwest, and Saturn with Antares 14-16 degrees to its lower right, in the southwest. Lonely Fomalhaut is in the southeast, in a rather barren area of the sky. Note the seasonal westward motions of the stars. The slow-moving outermost easy naked-eye planet Saturn, taking nearly 30 years to make one trip around the zodiac, gets dragged along with the stars’ seasonal motions. This month, telescopes show Saturn’s rings 27 degrees from edge-on, the maximum possible.

Arcturus is 33 degrees above the midday sun on Oct. 29, and is up nearly three hours longer than the sun, so for several days in late October and early November, you can catch Arcturus at two separate times: low in the east-northeast at dawn, and low in the west-northwest at dusk.

The first moon of the new cycle occurs on Friday, Oct. 20. Begin looking for the 2 percent crescent 6 degrees up in the west-southwest at civil twilight, when the sun is 6 degrees down, some 25 minutes after sunset, or 6:31 p.m. in Palm Springs and the western Coachella Valley. Mid-twilight (when the sun is 9 degrees down) occurs at 6:46 p.m., with the moon only 3 degrees up. To catch the 30-31 hour crescent, you’ll need to go to a place such as Desert Hot Springs or the far eastern Coachella Valley, where high mountains won’t block your view.

Within an hour after sunset on Sunday, Oct. 22, can you spot Antares 9 degrees to the lower left of the 10 percent crescent moon? On Monday, Oct. 23, the moon is in the southwest and 17 percent full, with Antares 12 degrees to its lower right and Saturn 6 degrees to the left. On Oct. 24, Saturn is 7 degrees to the moon’s lower right. The crescent is then nearly one-quarter full, but we must wait until the afternoon and evening of Oct. 27 to catch the first quarter moon, half full and 90 degrees east of the sun.

The website of the Astronomical Society of the Desert has a listing of our star parties. The primary location is at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument (on Highway 74, within four miles south of Highway 111 in Palm Desert). Sessions are scheduled there on Oct. 28 from 7 to 10 p.m., and on Nov. 25 and Dec. 23, from 5 to 8 p.m. Sawmill Trailhead, our high-altitude site (elevation 4,000 feet—wear warm clothes), will have star parties starting at dusk on Sat. Oct. 14, Nov. 11, and Dec. 9. Also, check out the Sky’s the Limit Observatory and Nature Center in Twentynine Palms, at skysthelimit29.org.

Wishing you clear skies!

Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing sky watching opportunities for school children in and around Palm Springs. Robert D. Miller did graduate work in Planetarium Science and later astronomy and computer science at Michigan State University, and remains active in research and public outreach in astronomy.

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