The Sky This Week from Aug. 22 to 29: A Black Moon

Sky This Week is brought to you in part by Celestron.

Friday, August 22
Reaching its highest point in the sky around 11 P.M. local daylight time tonight is the Swan Nebula (M17). This gorgeous deep-sky object is a fan favorite of amateur astronomers thanks to its brightness, which makes it easy to find and observe in any instrument. Located in northwestern Sagittarius, you can view this emission nebula through binoculars, although a telescope of any size will bring out more detail. It sits near the border of Sagittarius, Scutum, and Serpens Cauda — look 2.6° southwest of magnitude 4.7 Gamma (γ) Scuti to find it. 

Glowing at magnitude 6.0 and covering an area some 20′ by 15′, the Swan is so named because it looks like the eponymous bird as it glides along the still surface of a lake, long neck arched. Some observers also call it the Omega Nebula because it also looks a bit like the Greek letter Omega (Ω). As an emission nebula, its gas shines because it is excited by nearby stars; however, these stars are not visible, as they lie hidden within the gas and dust of the nebula. 

Sunrise: 6:18 A.M.
Sunset: 7:46 P.M.
Moonrise: 5:28 A.M.
Moonset: 7:43 P.M.
Moon Phase: New
*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 23
New Moon occurs at 2:07 A.M. EDT. This particular New Moon has been garnering headlines as a Black Moon — specifically, a seasonal Black Moon. This is a non-scientific name that can be attributed to the third of four New Moons to occur in an astronomical season — e.g., between the summer solstice and the autumnal equinox. 

Black Moons occur about once every 2.8 years, or roughly as often as Blue Moons. However, Black Moons cannot be seen, because the Moon is invisible to us at New Moon. This phase occurs when the Moon stands between Earth and the Sun, so the nearside is completely in shadow. So despite all the hype, there will be nothing Moon-related to see in the sky today! (Don’t worry, though — the young crescent Moon will soon put in an appearance.) 

However, the lack of a Moon opens up a treasure trove of other objects that are best seen when the sky is dark. Reaching an altitude of some 50° in the east by 10 P.M. local daylight time is NGC 7331, a galaxy in far northern Pegasus and the brightest member of the Deer Lick Group. Also known as Caldwell 30, NGC 7331 is a flocculent spiral, meaning its arms are patchy rather than showing off a smooth glow. Shining at magnitude 9.5, you can spot it in binoculars or any telescope (the bigger the better, if you’re after more detail) some 4.3° north-northwest of 3rd-magnitude Eta (η) Pegasi. It spans roughly 10’ and is much longer than it is wide, given the way it is tilted toward us and appears almost edge-on. Larger scopes may show a few other, smaller galaxies nearby. 

Sunrise: 6:19 A.M.
Sunset: 7:45 P.M.
Moonrise: 6:36 A.M.
Moonset: 8:06 P.M.
Moon Phase: New

Sunday, August 24
Mars is just less than 3° south of the gorgeous double star Porrima (Gamma Virginis) this evening. At magnitude 1.6, Mars is about a full magnitude brighter than Porrima (magnitude 2.7); the star will appear to the planet’s upper right in the western sky an hour after sunset, when they are roughly 7° high. To the pair’s upper left is Spica, Virgo’s 1st-magnitude alpha star. 

Through a telescope, Mars’ tiny, 5”-wide disk won’t show off any detail, though it will appear to glow orangey-red. Skim up to Porrima to view its two components, looking almost like a perfect pair of headlights in the dark sky. Both stars are nearly identical in brightness (magnitude 3.8 and 3.7) and color (blue-white); each is roughly 1.5 times the Sun’s mass and has a temperature of about 7,100 K (compared to the Sun’s temperature of nearly 5,800 K). The two stars orbit each other every 169 years and are now about 4” apart on the sky. 

Sunrise: 6:20 A.M.
Sunset: 7:44 P.M.
Moonrise: 7:42 A.M.
Moonset: 8:27 P.M.
Moon Phase: Waxing crescent (2%)

Monday, August 25
Observers who are quick to step outside after sunset can catch a delicate crescent Moon sinking in the west, now just 8 percent lit as sunrise begins to creep over the lunar nearside. 

Magnitude 1.6 Mars sits 7° to the upper left (east) of the Moon, slowly becoming visible as the sky darkens. You can catch it a little earlier if you search with binoculars or a telescope, which will likely also show earthshine on the Moon, as sunlight bounces off Earth and illuminates the regions of the Moon still in our planet’s shadow.

Above the trio, the bright magnitude –0.1 star Arcturus will quickly pop out of the twilight. This aging red giant is some 25 times the width of our Sun and more than 100 times as bright as our star; however, Arcturus has a much lower surface temperature than the Sun, as stars cool as they age. 

Some 1.5 to 2 hours after sunset, the sky has grown dark enough to easily observe fainter deep-sky objects. Now, let’s look about 10° north of Arcturus to find the globular cluster NGC 5466, which glows at 9th magnitude in southwestern Boötes, near the constellation’s border with the smaller Canes Venatici.

NGC 5466 is a small but loosely packed cluster covering about 11’ on the sky. Just over 50,000 light-years from Earth, it contains stars some 12 billion to 13 billion years old. This faint cluster can be hard to spot, but the dark sky with no Moon should aid your search. If you can find the much brighter (and more famous) globular M3 in Canes Venatici, note NGC 5466 lies a little over 5° due west of this object. 

Sunrise: 6:21 A.M.
Sunset: 7:42 P.M.
Moonrise: 8:45 A.M.
Moonset: 8:47 P.M.
Moon Phase: Waxing crescent (6%)

Monday, August 25
Observers who are quick to step outside after sunset can catch a delicate crescent Moon sinking in the west, now just 8 percent lit as sunrise begins to creep over the lunar nearside. 

Magnitude 1.6 Mars sits 7° to the upper left (east) of the Moon, slowly becoming visible as the sky darkens. You can catch it a little earlier if you search with binoculars or a telescope, which will likely also show earthshine on the Moon, as sunlight bounces off Earth and illuminates the regions of the Moon still in our planet’s shadow.

Above the trio, the bright magnitude –0.1 star Arcturus will quickly pop out of the twilight. This aging red giant is some 25 times the width of our Sun and more than 100 times as bright as our star; however, Arcturus has a much lower surface temperature than the Sun, as stars cool as they age. 

Some 1.5 to 2 hours after sunset, the sky has grown dark enough to easily observe fainter deep-sky objects. Now, let’s look about 10° north of Arcturus to find the globular cluster NGC 5466, which glows at 9th magnitude in southwestern Boötes, near the constellation’s border with the smaller Canes Venatici.

NGC 5466 is a small but loosely packed cluster covering about 11’ on the sky. Just over 50,000 light-years from Earth, it contains stars some 12 billion to 13 billion years old. This faint cluster can be hard to spot, but the dark sky with no Moon should aid your search. If you can find the much brighter (and more famous) globular M3 in Canes Venatici, note NGC 5466 lies a little over 5° due west of this object. 

Sunrise: 6:21 A.M.
Sunset: 7:42 P.M.
Moonrise: 8:45 A.M.
Moonset: 8:47 P.M.
Moon Phase: Waxing crescent (6%)

Tuesday, August 26
Asteroid 6 Hebe reaches opposition this morning at 10 A.M. EDT. Shining at magnitude 7.5, Hebe is located in Aquarius and rises shortly after sunset, remaining visible all night. You should be able to spot in binoculars or any small telescope. The best time to observe it is late in the evening and overnight into the early-morning hours, as that’s when the asteroid is highest in the sky. Around local midnight, Hebe is 30° high in the south, about 13.5° to the upper right of the 1st-magnitude star Fomalhaut in Piscis Austrinus. Much closer is 3rd-magnitude Skat in Aquarius; Hebe stands just under 6° west-southwest of this star tonight. 

The Moon passes 3° south of Mars at 1 P.M. EDT. If you prefer to observe earlier in the evening, you can catch the pairing low in the west an hour after sunset, when they are still about 5° above the horizon. If you recall Porrima’s location from earlier in the week, this star now lines up with Mars and the Moon to form a line in the sky, with Mars in the middle. The 3.8-day-old Moon is now some 14 percent lit. Bright Spica sits 7° to the Moon’s upper left; our satellite will pass due south of this star tomorrow morning. 

Sunrise: 6:22 A.M.
Sunset: 7:41 P.M.
Moonrise: 9:47 A.M.
Moonset: 9:08 P.M.
Moon Phase: Waxing crescent (12%)

Wednesday, August 27
The Moon moves 1.2° south of Spica during the daylight hours, sitting due south of Virgo’s luminary at 11 A.M. EDT. By this evening, a new line has formed in the sky, with Spica now between Mars and the Moon, which sits to the star’s left. An hour after sunset, Spica is still some 7° high in the west, so take some time to enjoy the view before the region sets.

While your eyes are on this part of the sky, look to the Moon’s upper left, where you’ll encounter the constellation Libra. Its two brightest stars — Alpha (α) and Beta (β) Librae — are roughly the same magnitude, although Beta is a tad brighter at magnitude 2.6 (Alpha is magnitude 2.8). But Alpha is the one that deserves your attention tonight. 

Also called Zubenelgenubi, this is a double star that is within the ability of the naked eye to separate! Its components are 4’ apart, with the brighter of the two shining at magnitude 2.8 and the fainter companion to the northwest, shining at magnitude 5.2. That fainter star is cataloged as Alpha¹ Lib, while Zubenelgenubi itself is Alpha². Even if you have trouble seeing them with your eyes, binoculars or any telescope will readily separate them. With magnification, they form a lovely contrasting pair, as the brighter star shines blue-white and the fainter star orangey-yellow.

Sunrise: 6:23 A.M.
Sunset: 7:39 P.M.
Moonrise: 10:48 A.M.
Moonset: 9:30 P.M.
Moon Phase: Waxing crescent (19%)

Thursday, August 28
Comet C/2024 E1 (Wierzchoś) is passing less than 0.5° from magnitude 5.4 Lambda (λ) Coronae Borealis in the western sky this evening. The comet is quite faint at 15th magnitude, so you’ll want a dark observing site and a large scope to net it. Fortunately, you have the luxury of waiting until the sky is fully dark — even by 10 P.M. local daylight time, Wierzchoś is still 50° high. 

At that time, look for Corona Borealis, whose curved figure sits above Boötes the Herdsman, who is anchored by the bright star Arcturus. Wierzchoś is located in a relatively sparse region of sky in northern Corona Borealis, just west of the star Eta Herculis in the Keystone of Hercules. 

Tonight, Wierzchoś is some 18’ northwest of Lambda, so once you find this star, you’ll have the comet within your field of view and can bump up the magnification until you spot it. You can return tomorrow to see that Wierzchoś has moved southwest of the same star, still roughly the same distance away. 

Sunrise: 6:24 A.M.
Sunset: 7:37 P.M.
Moonrise: 11:50 A.M.
Moonset: 9:54 P.M.
Moon Phase: Waxing crescent (27%)

Friday, August 29
Let’s check in with the moons of mighty Saturn this evening, as Titan stands east of the planet and Iapetus is far to the west, the latter approaching its greatest western elongation tomorrow. You can find the ringed planet already 15° high in the east at 10 P.M. local daylight time, continuing to rise until around 2:30 A.M., when it reaches the highest point in its path through our sky. 

The magnitude 0.7 planet is the brightest point of light in southwestern Pisces, hanging below the Circlet asterism as it rises. Through a telescope, you’ll readily spot the magnificent rings, which stretch some 43.5” from end to end and are tilted by a mere 2°. 

Titan is just over 3’ east of Saturn, shining brightest of all the planet’s moons at mid-8th magnitude. Moving inward toward the planet from the east, at 10 P.M. CDT you’ll find first Rhea and then Dione, both shining at 10th magnitude. On the western side of the world at that time is Tethys, also 10th magnitude, and then finally Iapetus, nearly 9.5’ west of the planet. Iapetus is at its brightest, its icy hemisphere turned toward Earth so that it reflects enough sunlight to also reach 10th magnitude. 

Sunrise: 6:25 A.M.
Sunset: 7:36 P.M.
Moonrise: 12:53 P.M.
Moonset: 10:23 P.M.
Moon Phase: Waxing crescent (36%)