During October, only three planets can be easily spotted with the unaided eye.
Saturn is visible all night on Oct. 3 and 4, as Earth passes between the sun and the ringed planet—so it then appears in the night sky at opposition, nearly 180° from the sun. At dusk, find Saturn gradually ascending from the east into the east-southeast, while fading slightly from magnitude +0.3 to +0.5. At dawn, find Saturn descending in the west, reaching the horizon by mid-month. You can still view Saturn in the morning by looking at least 2 1/2 hours before sunup at month’s end.
The two other planets are bright Jupiter, near magnitude -2.0, and Mars, near magnitude +1.0. During morning twilight, find them well up in the east to southeast, nearly 18° apart on Oct. 1, shrinking to within 6° at month’s end. Mars now is shifting eastward against the stars by 0.6° to 0.5° per day. It’ll be very interesting to follow with binoculars for a few days before and after Oct. 11, when the red planet passes through the Beehive, a cluster of stars of magnitude 6 and fainter. The star Regulus, heart of Leo, the Lion, is not far east of the pair of planets. Watch Jupiter creep slowly toward Regulus this month, closing the distance from 10.5° to less than 6°.
There’ll be many striking gatherings involving Mars, Jupiter and Regulus in the coming months, to be illustrated in the Abrams Planetarium Sky Calendar (available by subscription for $12 per year, from abramsplanetarium.natsci.msu.edu/sky-calendar) and described in future editions of this column.
The moon opens October in the morning sky in gibbous phase, about 10° from Aldebaran, eye of Taurus. On Oct. 3, it’s in Gemini, at last-quarter phase, half full, and 90°, or a quarter-circle, west of the sun. The next morning, Oct. 4, the moon stands as a fat crescent, 5° to 7° from the “Twin” stars, Pollux and Castor. On Oct. 5, the waning crescent stands to the lower left of Mars and very close to the Beehive cluster. Using binoculars, can you see any of its stars in the glare of the moon? On the morning of Tuesday, Oct. 6, as seen from western U.S., the crescent moon stands with its earth-lit upper edge close to the lower left of Jupiter. Farther east in the U.S., the moon occults, or covers, Jupiter, but here, even as they rise some four hours before sunrise, the event is already over. If you rise that early, watch the moon gradually pull away from Jupiter until dawn. Using binoculars, can you still spot Jupiter at sunrise?
At dawn on Oct. 7, the moon appears below Regulus. The crescent is visible for two additional mornings, but you’ll need to look in brighter twilight to see the thin, old 1 percent crescent on Oct. 9, within 27 hours before the new moon.
Venus shines at magnitude -4 or brighter, but is still difficult to see, as it appears not far from the sun. The best chances to catch it in the evening sky occur near the start of the month. During Oct. 1-7, Venus sets 38 to 21 minutes after sunset in Reno. You’ll need an unobstructed view to the left of the sunset direction and very clear skies—plus binoculars would help! Binoculars will reveal the crescent phase of Venus, which thins from 14 percent to 9 percent during the first week. Can you spot Mercury 5° to the upper right of Venus on Oct. 6? The moon’s pairing with Venus on Oct. 11 will set so soon after sunset that it is not likely to be seen.
The pairing of the crescent moon with Antares low in the southwest at dusk on Oct. 14 will be very pleasing for binoculars. Watch the gibbous moon skip above Saturn on the evenings of Oct. 23 and 24. The full moon occurs on Sunday night, Oct. 25. After nightfall on Oct. 27, watch the waning gibbous moon rise just to the lower left of the Pleiades cluster and pull away for the rest of the night.
On Saturday morning, Oct. 31, there’s a list of wonders worth getting up before dawn to see. Blue-white Sirius, the brightest star, reaches its high point, 40° up. The star is outshone by steady, bright, yellowish Jupiter, high in the eastern sky. This morning, Jupiter stands midway between two companion objects: red Mars, to its upper right, and blue-white Regulus, to Jupiter’s lower left. The three bodies stand in a slightly bent line at intervals of just less than 6°.
As twilight just gets under way on Oct. 31, the waning gibbous moon, two-thirds full, reaches its high point just south of overhead. Pollux and Castor stand 5°-7° to its north. In the southwest stands Orion, the Hunter, immediately recognizable by his three-starred belt with red Betelgeuse above and blue-white Rigel below. Extend the belt to the left to Sirius, the Dog Star, and to the right to reddish Aldebaran, the eye of Taurus, the Bull. A huge oval or hexagon of stars, comprising six stars of first-magnitude or brighter (and a seventh within), has just entirely crossed into the western half of the sky as twilight brightens at the end of October. In clockwise order from Sirius, the remaining stars of the Hexagon are Procyon, Pollux (closely accompanied by Castor, of magnitude 1.6), Capella (the “Mother Goat” star in the northwest), Aldebaran, Rigel and back to Sirius. Betelgeuse lies inside the Winter Hexagon.
As twilight brightens, watch for the rising of the stars Arcturus, the bear-watcher, in the east-northeast, followed by Spica, the spike of grain, in the east-southeast. If you first locate the Big Dipper standing on its handle in the northeast, extend its curved handle to “follow the arc to Arcturus, and drive a spike to Spica.” As twilight brightens further, watch for the rising of brilliant Venus, just 3.7° to the lower right of Spica. By the time Venus appears, you’ll probably need binoculars to see Spica, but Venus will remain in view until nearly sunrise. A telescope and even a pair of binoculars will reveal Venus as a thin crescent, just 2 percent full and a full arcminute (1/60 of a degree) in diameter. Venus passed inferior conjunction, nearly between Earth and the sun, on Oct. 24, and has just begun what will become a spectacular appearance as a morning “star.” Watch Venus make a tight loop around the star Spica in November as both rise higher into a dark predawn sky.
Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys promoting sky watching to folks of all ages in and around Palm Springs and East Lansing, Mich. Robert Miller, who provided the twilight charts, 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.
