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The Sky This Week: Observe the Moon

Against the backdrop of a Full Moon, two planets stand still and the Orionid meteor shower peaks from October 15 to 22.
Moon setting with trees
Setting satellite
The bright Moon sets in this photo taken October 1, 2012.
VinceFL (Flickr)

Friday, October 15
The Moon passes 4° south of Jupiter in Capricornus at 6 A.M. EDT. You can’t see them then — both are below the horizon — but they are visible in the sky tonight after sunset. By then, the Moon has shifted over into Aquarius and sits 8.2° east-southeast of Jupiter. The bright star Deneb Algedi (magnitude 2.9) sits between them, about one-third of the way on a line drawn from Jupiter (magnitude –2.6) to the Moon.

Look to the right (west) of Jupiter and you’ll find Saturn, glowing softly at magnitude 0.5 on the other side of Capricornus. It sits 6° southeast of Beta (β) Capricorni. The ringed planet looks stunning through a telescope, with its trademark rings stretching 40" and several small moons around it, including Enceladus, Rhea, Dione, and Tethys. Brighter Titan sits just over 2' away, currently west-southwest of the planet.

Sunrise: 7:11 A.M.
Sunset: 6:20 P.M.
Moonrise: 4:28 P.M.
Moonset: 1:46 A.M.
Moon Phase: Waxing gibbous (77%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.

Saturday, October 16
Venus passes 1.5° north of the red giant Antares in Scorpius this morning at 10 A.M. EDT. Like Jupiter and the Moon yesterday, however, the two aren’t visible at that time, so instead step outside after sunset to spot them, roughly the same distance apart and hanging low in the southwest, about 12° above the horizon 15 minutes or so after sunset. Venus is a bright magnitude –4.4, far outshining the 1st-magnitude star.

Tonight is also International Observe the Moon Night. Our satellite, which is a waxing gibbous whose face is between 50 percent and 100 percent lit, rises around 5 P.M. local time and is visible all evening in eastern Aquarius. NASA is hosting several activities in honor of the event, including a NASA TV broadcast you can tune in to from 7:30 P.M. to 8:30 P.M. EDT tonight.

Observing the Moon can be as simple as casting your gaze upward, or as complex as training a telescope on its rugged surface to make out fine details. Tonight, because our Moon is mostly illuminated, many of its features are on display, with only its western limb (east in our sky) still hidden in shadow. Look for features such as the Seas of Serenity, Tranquillity, and Showers; as well as large craters such as Tycho, Langrenus, and Copernicus.

Sunrise: 7:12 A.M.
Sunset: 6:18 P.M.
Moonrise: 4:57 P.M.
Moonset: 2:54 A.M.
Moon Phase: Waxing gibbous (85%)

Sunday, October 17
The Moon passes 4° south of Neptune at 10 A.M. EDT. By this evening, they’re 5.8° apart at sunset and rising higher as darkness falls. Once twilight is gone, try finding the solar system’s most distant planet with binoculars or a telescope. Its magnitude 7.7 glow sits 3.5° east-northeast of Phi (ϕ) Aquarii, which itself shines at magnitude 4.2.

Mercury is stationary at 9 P.M. EDT, but isn’t visible in the evening due to its position relative to the Sun. Instead, you’ll want to catch it in the morning, when it’s 7° high 30 minutes before sunrise. The small planet is magnitude 1.1 and just over 2° south-southwest of the star Porrima in Virgo. Its disk appears 9" wide in binoculars or a telescope and is a small crescent just 19 percent lit.

Mercury was previously moving northwest (retrograde) at a steady clip; now, it will swing around and begin moving southeast (prograde).

Sunrise: 7:13 A.M.
Sunset: 6:17 P.M.
Moonrise: 5:22 P.M.
Moonset: 4:00 A.M.
Moon Phase: Waxing gibbous (92%)

Monday, October 18
Next, it’s Jupiter turn to stand stationary against the background stars. It comes to a halt in Capricornus at 7 A.M. EDT. The gas giant, which had been moving southwest, will now swing around and begin sliding northeast, pulling away from Deneb Algedi.

Because the planet sets two hours after midnight, the best time to catch it is this evening after dark. And tonight, Ganymede is just about to slip onto Jupiter’s large disk at sunset in the Eastern time zone. The moon then takes just over 3½ hours to cross the planet’s face, moving from east to west.

If you stick around longer, Ganymede’s shadow slips onto the disk just after 11 P.M. EDT, followed by the small moon Io around 1 A.M. EDT on the 19th. Io’s shadow eventually follows, too, and observers with clear skies at 2:20 A.M. EDT on Tuesday morning (11:20 P.M. PDT on Monday night) will glimpse a three-for-one: Ganymede’s shadow about to slide off Jupiter’s western limb, with bright Io slightly more than midway across the disk and its own smaller shadow near the eastern limb.

Sunrise: 7:14 A.M.
Sunset: 6:15 P.M.
Moonrise: 5:46 P.M.
Moonset: 5:04 A.M.
Moon Phase: Waxing gibbous (96%)

Tuesday, October 19
Hidden within Hercules the Strongman is a spectacular ball of ancient stars often called the Hercules Globular Cluster. Cataloged as M13 in Messier’s not-a-comet list, this ancient cluster was discovered by Edmond Halley (for whom the famous comet is named) in 1714.

You’ll find M13 2.5° south of Eta (η) Herculis, which shines at magnitude 3.5. The cluster itself glows at magnitude 5.8 and spans about 20' — nearly the size of the Full Moon. Because the Moon is also up in the sky tonight, you’ll likely need binoculars or a small scope to tease out this cosmic fuzzball from the background. But note its position and come back when there is no Moon out, and you may see it without any optical aid at all. M13 contains more than 100,000 stars and is so dense that in some cases, stars within the cluster collide, creating younger-looking stars called blue stragglers.

Sunrise: 7:15 A.M.
Sunset: 6:14 P.M.
Moonrise: 6:08 P.M.
Moonset: 6:06 A.M.
Moon Phase: Waxing gibbous (99%)
Aristoteles crater

Wednesday, October 20
Full Moon occurs at 10:57 A.M. EDT. October’s Full Moon is often called the Hunter’s Moon. And it’s the perfect time to return to the crater Aristoteles in the lunar north, which we visited last week.

Observing the Full Moon with a telescope can be a bit eye-watering, but pop in a filter or bump up your magnification to cut down on the amount of light traveling through your scope and into your eye. Do note that even then, your night vision will suffer, so if you plan to do any other observing, you might want to get it in before you swing your gaze to the Moon.

Once you’ve got Aristoteles and its neighbor Exodus in your sights, compare them to the image above, taken at a different Sun angle, to see how a few days can completely change the look of the lunar surface. Now, the Sun is high overhead, and Aristoteles looks like an oval of light-colored material near circular Exodus. Any small secondary craters visible around Aristoteles last week are now gone, washed out of view until the Sun starts to set from the opposite direction.

Sunrise: 7:16 A.M.
Sunset: 6:13 P.M.
Moonrise: 6:31 P.M.
Moonset: 7:08 A.M.
Moon Phase: Full
Orionid meteor shower peak October 2021
Orionid meteor shower
The Orionids’ radiant in northeastern Orion rises after 10:30 P.M. local time.
Astronomy: Roen Kelly

Thursday, October 21
The Orionid meteor shower peaks today, but the fainter meteors will have a hard time contending with the still-bright Moon. Our satellite will unfortunately bump down the number of shooting stars you’ll see from the shower’s maximum expected rate of 20 meteors per hour at peak.

Still, if you want to try your luck, the shower’s radiant, which sits 10° north of Betelgeuse in Orion the Hunter, rises around 10:30 P.M. local time this month. But your best bet is to step outside early this morning, when the radiant is 65° high two hours before sunrise and the Moon is several constellations away in Aries. The shower will remain active for another week and a half, but rates will drop dramatically after today’s peak passes.

Speaking of the Moon, our satellite passes 1.3° south of Uranus at 6 P.M. EDT. The pair rise around 7 P.M. local time, now just over 2° apart in eastern Aries the Ram. Uranus, which is often visible to the naked eye under clear, dark skies, will definitely need some optical aid to spot tonight. Its magnitude 5.7 glow will be lost in the glare of the Moon’s bright light, but you may pick it up with binoculars or a telescope, sitting northeast of the Moon and 11.7° southeast of Aries’ alpha star, Hamal.

Sunrise: 7:17 A.M.
Sunset: 6:11 P.M.
Moonrise: 6:56 P.M.
Moonset: 8:09 A.M.
Moon Phase: Waning gibbous (99%)

Friday, October 22
There’s a dark window tonight between sunset and moonrise when you might be able to catch sight of some of the sky’s fainter objects. Let’s seek out the Owl Cluster (NGC 457), an open cluster in Cassiopeia the Queen that bears a resemblance to the bird for which it is named. (Of course, amateur astronomers are quite creative and this cluster has several other names as well, including the E.T. Cluster and the Kachina Doll Cluster.)

Located 2° southwest of Ruchbah (Delta [δ] Cassiopeiae), the Owl Cluster’s two brightest stars, Phi Cassiopeiae and HD 7902, serve as the bird’s eyes. Neither is actually part of the cluster, however, and instead sit in front of its member stars. With its wings spread, the owl’s body stretches to the northwest. Binoculars or a small scope should show many of the roughly 80 stars that make up this young grouping of stars. They formed some 21 million years ago — a cosmic eyeblink, in terms of the universe’s age.

Sunrise: 7:19 A.M.
Sunset: 6:10 P.M.
Moonrise: 7:24 P.M.
Moonset: 9:10 A.M.
Moon Phase: Waning gibbous (96%)


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