October provides sky watchers the moon in conjunction with the two brightest planets, Venus and Jupiter; good chances to spot those planets with the unaided eye in the daytime just after sunrise; and a major solar eclipse on Saturday, Oct. 14, when the moon is in transition from morning skies to the evening.
Look daily one hour before sunrise, and watch the moon wane from full, low in the west on Sept. 29, to a thin crescent, low in the east, on Oct. 13. In Aries in the western sky on Sunday morning, Oct. 1, the waning gibbous 94 percent moon is nearly halfway from horizon to overhead, with bright Jupiter 9° to its upper left. Venus, even brighter, is behind you in Leo, and nearly 30° up in the east. Note the 1.4-magnitude star Regulus, heart of Leo, 7° to Venus’ lower left.
On Oct. 1, keep track of the moon and Jupiter until sunrise to notch a daytime sighting of Jupiter. Binoculars will make it easier, and you’ll notice that Jupiter shows a perceptible disk. The next morning offers another chance, with Jupiter within 7° to the lower left of the 87 percent moon.
In October, Venus gleams at magnitude -4.7 to -4.4, slightly faded from its peak in mid-September. This month, Venus changes in phase and apparent size, from 37% full and 32” (arcseconds) across on the 1st, fattened to 54% but shrunk to 22” across on the 31st. This month, Venus climbs to its greatest altitude in the morning twilight sky. It is four to six times as bright as Jupiter, which shines at magnitude -2.8 to -2.9. Our solar system’s largest planet shows a full disk, growing from nearly 48” on Oct. 1 to 49.5” at closest approach in early November.
On October mornings an hour before sunrise, the positions of stars in the sky—but not those of the moon and the planets—are the same as they’ll be on March evenings about an hour after sunset. Find Sirius, the brightest star, but not as bright as Venus or Jupiter, flashing vigorously in the southern sky, on a line formed by extending the belt of Orion toward the southeast. Find Aldebaran and the Pleiades by extending Orion’s belt in the opposite direction.
In the morning sky, you can also view Mercury in brightening twilight to the lower left of Venus, by 30° on Oct. 1, increasing 1° per day to 37° on Oct. 8. Mercury passes superior conjunction on the far side of the sun on Oct. 19-20.
Continuing its eastward journey through the zodiac constellations at a rate averaging 13° per day, the moon on Oct. 3 is 79% full in Taurus, within 4° to the upper left of the Pleiades cluster, and 11° right of Aldebaran, eye of the Bull.
On the morning of Oct. 5, the 60% moon resides in the northernmost section of the zodiac, near the foot of Castor in Gemini, passing just 6° south of overhead 1.2 hours before sunrise.
On Oct. 6, nearing last quarter phase (90° or a quarter-circle west of the sun), the 51% moon is 9-11° west of the “Twin” stars, Castor and Pollux. On Oct. 7, the moon is now a crescent at 41%, 2-7° below the Twins.
On Sunday, Oct. 8, look a little earlier, 1 1/2 hours before sunrise, and use binoculars to see the Beehive star cluster in Cancer, within 4° to the lower right of the 32% crescent moon. An hour before sunrise on Oct. 9, Regulus and Venus appear closest together this morning, 2.3° apart, and are within 13° to the lower right of the 23% moon.
On Tuesday Oct. 10, it’s just four days until the solar eclipse! This morning, an hour before sunrise, see the 16% crescent moon in the east with its darker side illuminated by earthshine. Venus, within 6° to the moon’s lower right, itself shows a crescent, 43% illuminated and nearly 29” across. Regulus is 2.4° to the upper left of Venus. Keep Venus in view as sunrise approaches, and you may be able to snag a daytime sighting.
On Thursday, Oct. 12, one hour before sunup, the moon is 11° up in the east, with Venus 22° to its upper right. The sun is below the horizon, 24° to the moon’s lower left.
On Friday the 13th, one hour before sunrise, the moon isn’t in view yet, so we’ll wait until about 40 minutes before sunup to catch the 1 percent crescent just 3-4° above the horizon and 4° south of east, and 34° to the lower left of Venus. The sun is below the horizon, within 13° to the moon’s lower left.
Saturday, Oct. 14—it’s solar eclipse day!
From Reno, the solar eclipse begins at 8:05 a.m., as the moon’s disk begins to encroach upon the sun’s, near the very top of the sun’s disk. The sun is then in the east-southeast, 10° up. The moon gradually covers more of the sun’s disk until 9:21 a.m., when the moon will cover 90 percent of the sun’s diameter (the magnitude of the eclipse) and 85 percent of the area of the solar disk (called the obscuration). The sun will then be 37° east of south, and 35° above the horizon. The eclipse will conclude at 10:45 a.m., when the moon’s disk will depart from the lower left edge of the sun’s disk, near the 7 o’clock position if you imagine the solar disk to be a clock face.
If you intend to observe the eclipse, it is very important to do so safely. Viewing the sun improperly can cause permanent damage to eyesight. The American Astronomical Society has compiled a list of vendors of solar filters which would provide a safe means to observe. During all stages of this eclipse, just as before and after when the sun is fully visible, it is important to look at the sun only with suitable eye protection.
After the Oct. 14 solar eclipse, the moon sets too soon after sunset on Oct. 15 to be seen easily. Your first good chance to see the waxing crescent moon after new, if you have an unobstructed view, will come on Monday, Oct. 16. About 40 minutes after sunset, look for the 6% young crescent 4° up in the west-southwest.
On Oct. 17 and 18, look for the red supergiant star Antares, heart of Scorpius, near the moon: 7° to the moon’s upper left on the 17th, and 6° to the moon’s lower right on the 18th.
On Oct. 19, one hour after sunset, the southernmost moon, 28% full, is in the southwest to south-southeast, just to the west of the Teapot asterism in Sagittarius, the Archer. Mercury is at superior conjunction on the far side of the sun, and will emerge into the evening sky in December. On the next evening, the 38% moon is near the handle of the Teapot.
On Oct. 21, the moon is nearing first quarter phase, 90 degrees or one quarter-circle east of the setting sun. Note the moon’s shape is half full.
On Monday, Oct. 23, one hour after sunset, the 72% moon is in the south-southeast, with Saturn nearly 6° to its upper left. In late October and early November, the rings are tipped 10.5° from edge-on, the best view of the rings we’ll get until 2027. On Oct. 24, Saturn appears 10-11° to upper right of the 82% moon.
On the 27th, the 99% moon is in the east, with Jupiter 17° to the lower left.
On Oct. 28, the full moon is low, north of east an hour after sunset, with bright Jupiter within 3° to its lower left. Closest approach of Jupiter and the moon tonight occurs at 9:55 p.m. in Reno. On Sunday morning, Oct. 29, find the moon and Jupiter low in the west, with Jupiter 4° to the lower left of the moon.
The moon will rise later each evening, farther north each time until Nov. 1. By Oct. 31, the moon will rise after twilight ends. Each evening thereafter allows a longer interval of dark skies for evening deep-sky viewing.
For illustrations of many of these events consider subscribing to the Abrams Planetarium Sky Calendar, at abramsplanetarium.org/skycalendar. For $12 per year, subscribers will receive quarterly mailings of three monthly issues, each with an illustrated calendar of events with an evening star map on the reverse side.
Robert Victor originated the Abrams Planetarium monthly Sky Calendar in October 1968 and still helps produce an occasional issue. He enjoys being outdoors sharing the beauty of the night sky and other wonders of nature.