The Moon passes through Gemini this week, hanging with several planets in the predawn sky. Credit: Stellarium/USGS/Celestia/Clementine
Sky This Week is brought to you in part by Celestron.
Friday, August 15
Dwarf planet 1 Ceres reaches its stationary point in Cetus the Whale at 9 P.M. EDT. Previously it was moving eastward relative to the background stars. Now it will begin to move westward, or retrograde.
Ceres is only visible in the morning sky, but 4 Vesta is sliding eastward through the evening sky in Libra, still some 25° high in the southwest an hour after sunset. It’s located between that constellation’s two brightest stars: magnitude 2.8 Zubenelgenubi (Alpha [α] Librae) and slightly brighter magnitude 2.6 Zubeneschamali (Beta [β] Lib). This evening, Vesta is just east of the midpoint of a line drawn between these two stars, some 4.3° northeast of Alpha Lib.
Shining at magnitude 7.4, Vesta is well within the reach of binoculars or any telescope, even from the suburbs. It’s currently some 2.0 astronomical units from Earth, or nearly 186 million miles (299 million kilometers) away. (One astronomical unit, or AU, is the average Earth-Sun distance.) Vesta is moving relatively slowly — the easiest way to make sure you’ve spotted it is to sketch or photograph the area in your eyepiece tonight, and then return over the next few nights to repeat the exercise. The dot you notice moving from night to night is Vesta.
The fourth asteroid ever discovered, Vesta is the second-most massive world in the main belt, after Ceres, and the third-largest, after Ceres and 2 Pallas.
Sunrise: 6:12 A.M.
Sunset: 7:56 P.M.
Moonrise: 11:15 P.M.
Moonset: 1:32 P.M.
Moon Phase: Waning gibbous (56%)
*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, August 16
Last Quarter Moon occurs at 1:12 A.M. EDT as sunset sweeps across the lunar nearside following the Full phase last week. Visible in the early-morning sky, the Moon lies just under 4° west of the Pleiades in Taurus some two hours before sunrise, rising in the east. (The Moon will continue to creep closer to the cluster over the course of the day, occulting several stars in the Pleiades in an event visible from Japan, Korea, and northeast Asia.)
Uranus also lies in this region, some 4.4° southeast (to the lower right) of the Pleiades. You can use two closely spaced stars, 13 and 14 Tauri, to help point your way. This pair of 6th-magnitude suns sits 4.5° south of the Pleiades. Separated by some 21’, they are situated in an east-west line, with slightly dimmer 14 Tau marking the easternmost point. This morning, Uranus is 2.7° east of 14 Tau. Shining at magnitude 5.7, Uranus spans 4”, showing off a tiny disk through a telescope. It may appear as a slightly blue-gray, “flat”-looking star.
After plowing through the Pleiades, the Moon passes 5° due north of Uranus later today, at 4 P.M. EDT
Sunrise: 6:13 A.M.
Sunset: 7:55 P.M.
Moonrise: 11:58 P.M.
Moonset: 2:48 P.M.
Moon Phase: Waning crescent (44%)
Sunday, August 17
Nights are slowly shortening, but even as summer begins to wind down, the Summer Triangle still flies high in the sky overnight. Formed by three bright stars, this large asterism is highest around local midnight, when its center — through which the plane of the Milky Way flows — is some 70° high above the southwestern horizon.
At that time, if you are facing southwest, the lowest star in the Triangle is magnitude 0.8 Altair in Aquila the Eagle. Some 34° to its northwest (upper right) is magnitude 0.0 Vega, the alpha star of Lyra the Lyre. And about 24° to Vega’s upper left (northeast) is the third point in the Triangle and its highest star at this time, magnitude 1.3 Deneb in Cygnus the Swan. Covering some 415 square degrees — that’s more than 2,000 Full Moons — the Summer Triangle contains within its bounds a rich region of the Milky Way with plenty to see.
One such target is NGC 6910, a young open cluster shining at magnitude 7.5. It’s located about 0.5° from magnitude 2.2 Gamma (γ) Cygni, also called Sadr. This grouping looks best under higher magnification, showing up well in medium-sized telescopes, though it can be picked up in smaller scopes as well. With about 70 stars in total, this cluster is part of a much larger star-forming complex called the Cygnus OB9 Association, which lies some 5,600 light-years away. It is located within a cloud of hydrogen cataloged as IC 1318, which can be seen in deep-sky photographs of the region.
Sunrise: 6:14 A.M.
Sunset: 7:54 P.M.
Moonrise: —
Moonset: 4:01 P.M.
Moon Phase: Waning crescent (33%)
Monday, August 18
The second Titan shadow transit of the month occurs overnight tonight, so set your sights on Saturn late this evening. The ringed planet rises in the east around 9:30 P.M. local daylight time, gaining altitude hour by hour. Shining at magnitude 0.7, Saturn is easy to find as the brightest point of light in southwestern Pisces. Observers in the eastern half of the U.S. will have more time before the transit begins to center the ringed world in a telescope and enjoy the lovely view of the 43”-wide ring system surrounding the 19”-wide disk of the planet.
The shadow transit begins at 1:26 a.m. EDT, early on the 19th for half of the U.S. (still the 18th for those in the Mountain and Pacific time zones). The shadow appears at Saturn’s northeastern limb, moving from east to west. Note that mid-8th-magnitude Titan appears quite far from the planet, some 9” northeast of the limb where its shadow appears.
A few other moons should be visible as well: 10th-magnitude Dione, Tethys, and Rhea. Dione is east of Saturn, while Rhea is far west of the planet. Tethys is also west, but moving eastward as it heads for an occultation, first disappearing into the planet’s shadow just southwest of Saturn shortly after 3 A.M. EDT on the 19th.
Meanwhile, it takes about 2.5 hours for Titan’s shadow to travel halfway across the disk. The shadow then finally reaches the northwestern limb and the transit ends by 5:30 a.m. CDT on the 19th, after sunrise in the Eastern time zone.
This is the last time Titan’s shadow will transit with its moon too far from the planet to do the same. Next month, Titan will begin transiting Saturn as well.
Sunrise: 6:15 A.M.
Sunset: 7:52 P.M.
Moonrise: 12:50 A.M.
Moonset: 5:05 P.M.
Moon Phase: Waning crescent (23%)
Tuesday, August 19
Mercury reaches its greatest western elongation 19° from the Sun at 6 A.M. EDT. Now shining a bright magnitude 0, it stands 5° high in the east an hour before sunrise. The planet is now some 42 percent lit and 7” wide.
Mercury is located near central Cancer, just 2° south of M44, the Beehive Cluster, this morning. Although bright, the cluster will be difficult to spot in the encroaching twilight — if you observe from a relatively high elevation and have a clear eastern horizon, give them a try, using Mercury as a guide in binoculars or a telescope.
To Cancer’s upper right, Gemini the Twins is rising, dominated by bright Jupiter and Venus, now separated by 7° after their close conjunction last week. Jupiter shines at magnitude –2, while Venus shows off at magnitude –3.9. The two planets stand in line with the magnitude 3.5 star Delta (δ) Geminorum halfway between them this morning — check out the grouping 1.5 to 2 hours before sunrise, when the fainter star should still be visible before the sky begins to truly brighten.
Meanwhile, the crescent Moon appears 7° above Jupiter this morning; our satellite will pass 5° due north of the gas giant this afternoon at 5 P.M. EDT.
Sunrise: 6:16 A.M.
Sunset: 7:51 P.M.
Moonrise: 1:53 A.M.
Moonset: 5:59 P.M.
Moon Phase: Waning crescent (14%)
Wednesday, August 20
The Moon passes 5° north of Venus at 7 A.M. EDT; in the early-morning sky, Luna now floats to the upper left of the blazing planet, between that world and the magnitude 1.2 star Pollux in Gemini.
Although cataloged as the Twins’ beta star, Pollux is actually a tad brighter than Alpha Geminorum, also called Castor. This star sits above Pollux in the sky as the constellation is rising in the east this morning, and shines at magnitude 1.6.
Looking at Venus through a telescope, you’ll note the planet’s gibbous phase. It is 81 percent lit and spans 13” on the sky. To its upper right is Jupiter, which stretches 34” across — a testament to its standing as the largest planet in the solar system by far. Many observers this morning will see only three of Jupiter’s four Galilean moons: Io alone to the east, and Europa and Callisto to the west. Europa is slightly closer to Jupiter than Callisto.
Ganymede passes into the planet’s long, dark shadow some 30” from Jupiter’s western limb around 4:20 A.M. EDT this morning, shortly after the planet rises for those in the eastern half of the U.S. The moon moves through the shadow and then finally behind the giant planet later this morning, keeping it invisible as the planet rises out of the horizon haze farther west.
Sunrise: 6:17 A.M.
Sunset: 7:49 P.M.
Moonrise: 3:03 A.M.
Moonset: 6:41 P.M.
Moon Phase: Waning crescent (8%)
Thursday, August 21
The early-morning sky is still where all the activity is at today, as Venus passes 7° south of Pollux at 5 A.M. EDT and the crescent Moon is now close to Mercury, preparing to pass 4° north of the solar system’s smallest planet at noon EDT.
Let’s start in Gemini, which rises first and sits higher in the eastern sky before sunrise. An hour before the Sun crests the horizon, Venus is readily visible in eastern Gemini as the brightest point of light in this part of the sky. It lies to the lower right of Pollux, the brightest star in the Twins, with 4th-magnitude Kappa (κ) Gem about halfway between them. Jupiter is still in central Gemini, the second-brightest light in the sky and located to Venus’ upper right.
To the lower left of this scene is Cancer, now hosting the delicate crescent Moon above Mercury. At magnitude –0.3, Mercury is now easy to spot — the faintest of the three planets but still brighter than any star in this region of the sky. The Moon is now just 4 percent lit, quickly approaching New. If you look through a telescope, you’ll see Mercury has gained a bit of ground from earlier in the week and is now exactly half-lit. M44 — still challenging in twilight — sits about 3° above Mercury this morning, and will make a great target with binoculars or a telescope, especially earlier, before the sky grows too bright.
Sunrise: 6:17 A.M.
Sunset: 7:48 P.M.
Moonrise: 4:16 A.M.
Moonset: 7:16 P.M.
Moon Phase: Waning crescent (3%)
Friday, August 22
With no Moon in the evening sky, it’s time to check in with Comet C/2024 E1 (Wierzchoś), now in Hercules and visible for several hours after sunset.
By 9:30 P.M. local daylight time, Wierzchoś is still 60° high in the west. You’ll find it about 9.5° west of magnitude 3.5 Eta (η) Herculis, one of the four stars that make up the Keystone asterism. A closer signpost is magnitude 4.6 Chi (χ) Her, which tonight stands just less than 2° north of Wierzchoś.
This comet is currently still a target for larger scopes (8 to 10 inches or more), glowing faintly around 14th magnitude, though it is slowly brightening as it draws closer to the Sun, due to reach perihelion early next year.
There’s plenty else to observe in this region while you search for the comet, including NGC 6058, a planetary nebula some 7.5° west of Eta Her, along the path you’ll trace from this star to the comet. Alternatively, it’s just a short 2.8° jump southeast of Chi Her. NGC 6058 is a small nebula about 40” across that glows at magnitude 13, slightly brighter than the comet’s current brightness. The largest scopes (14 inches or more) will reveal a halo-like structure surrounding the nebula’s 14th-magnitude central star; smaller scopes will show it more as an evenly illuminated glow, though perhaps with a slightly brighter center.
Sunrise: 6:18 A.M.
Sunset: 7:46 P.M.
Moonrise: 5:28 A.M.
Moonset: 7:43 P.M.
Moon Phase: New
