The Sky This Week from May 17 to 24: The Moon visits Antares

The Moon occults two bright stars along the ecliptic as we also enjoy comets, asteroids, and star clusters in the sky this week.
By | Published: May 17, 2024

Friday, May 17
The Moon reaches apogee, the farthest point from Earth in its orbit, at 2:59 P.M. EDT. Luna will then sit some 251,432 miles (404,641 km) away.

By evening, the Moon is close to 4th-magnitude Zavijava (Beta [β] Virginis) in Virgo. How close? Many observers in the U.S. and Canada will see the Moon occult, or pass in front, of, this star overnight.

Note that the timing and duration of any occultation will depend on your location. Some will see the event late on the 17th, while for others it will take place in the early hours of the 18th. You can find a map of where the event is visible and the times it will occur in many major cities on the International Occultation Timing Association’s (IOTA) webpage. Note that times on this page are given in Universal Time.

While we’re focused on the Maiden, let’s also make a quick stop by a favorite double star: Gamma (γ) Vir, also called Porrima. The components of this beautiful binary system are now roughly 3″ apart, which is half the distance they’ll be at their greatest separation. They were last closest in 2005 and have a total orbital period of 169 years. Now easy to split, the stars have nearly identical magnitudes of 3.65 and 3.56 and, as Astronomy contributor Raymond Shubinski writes, “look like two tiny headlights in space.”

Sunrise: 5:43 A.M.
Sunset: 8:11 P.M.
Moonrise: 2:37 P.M.
Moonset: 2:58 A.M.
Moon Phase: Waxing gibbous (71%)
*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, May 18
Jupiter is in conjunction with the Sun at 3 P.M. EDT, rendering the gas giant invisible for now. It will reappear in our morning sky next month.

Comet 13P/Olbers is currently around 8th magnitude and sinking in the west within the boundaries of Auriga the Charioteer this evening after sunset. An hour after the Sun disappears, the comet is 15° high, about 4.5° due north of Beta (β) Tauri, a star that sits at the border of Taurus and Auriga.

Astrophotographers: Pull out your largest scope and favorite camera, and look about 1.2° northwest of Olbers. That will land you on the open cluster NGC 1893, which shines at magnitude 7.5 and stretches some 11′ across. This young gaggle of stars is embedded within the Tadpole Nebula (IC 410), also called the Tadpoles. IC 410 is so named for the two streamers of gas that look like tails in the northeastern region of the nebula. These tails stand out against the dust there, particularly in astrophotos. Tonight you can catch both a comet and this stunning nebular complex in a single shot!

Sunrise: 5:42 A.M.
Sunset: 8:12 P.M.
Moonrise: 3:37 P.M.
Moonset: 3:18 A.M.
Moon Phase: Waxing gibbous (79%)

Sunday, May 19
Asteroid 2 Pallas was the second world discovered in the main belt between Mars and Jupiter. It is the third-largest asteroid in the main belt. Pallas reaches opposition tonight at 11 A.M. EDT, shining at magnitude 9. You can find it amid the stars of Hercules, near that constellation’s Keystone asterism.

Let’s start with the Keystone, which stands 45° high in the east at 10 P.M. local daylight time tonight. It is made up of four stars: Pi (π), Epsilon (ϵ), Zeta (ζ), and Eta (η) Herculis. Tonight, Pallas lies some 6.3° southwest of magnitude 2.8 Zeta, the southwestern point of the Keystone. The main-belt world also lies just ¼° northwest of a slightly brighter 7th-magnitude field star.

Moving back to the Keystone, let’s use it to find a famous globular cluster: M13, also called the Hercules Globular Cluster or the great globular cluster in Hercules. It’s located about one-third of the way along a line drawn from Eta to Zeta Her, so about 2.5° south of Eta Her.

As its name suggests, M13 is both bright — magnitude 5.8 — and big, spanning 20′ (145 light-years in space at its distance from us). It also holds hundreds of thousands of stars and is a favorite target for many amateur astronomers. Visible to the naked eye when there is no Moon, you’ll likely need your binoculars or telescope to enjoy M13 tonight — either will do, as it looks fantastic even at lower magnification. And if you have a bigger scope, look carefully at the core for a faint, Y-shaped dearth of stars often called the propeller.

Sunrise: 5:41 A.M.
Sunset: 8:13 P.M.
Moonrise: 4:36 P.M.
Moonset: 3:37 A.M.
Moon Phase: Waxing gibbous (86%)

Monday, May 20
Let’s move on up from No. 2 to No. 1: Early risers this morning can catch the ruler of the main belt, dwarf planet 1 Ceres, floating off the handle of Sagittarius’ Teapot asterism in the south. Around 4 A.M. local daylight time, the region is some 25° high. Ceres is magnitude 8.2, a relatively easy catch with binoculars. It’s located just under 6.5° northeast of 3rd-magnitude Tau (τ) Sagittarii, which forms the point where the Teapot’s handle begins to curve inward and down toward the base. The largest main-belt world is also within 1° of a close pair of stars that are slightly brighter than Ceres at 5th to 6th magnitude. They lie to Ceres’ northeast.

Thanks to its location in the direction of the galactic bulge, Sagittarius is rich in deep-sky objects, including numerous globular clusters. One of these is M55, which shines at magnitude 6.3 and this morning lies just under 6° south-southeast of Ceres. A relatively “loose” globular, M55 spans some 19′ across — equivalent to 100 light-years in space. It contains roughly 100,000 members, which are some 12.5 billion years old. Try gradually stepping up the magnification on this one, from lower-powered eyepieces to higher ones, and watch how individual stars pop out in increasing numbers as you go.

Sunrise: 5:40 A.M.
Sunset: 8:13 P.M.
Moonrise: 5:38 P.M.
Moonset: 3:57 A.M.
Moon Phase: Waxing gibbous (92%)

Tuesday, May 21
The ringed planet Saturn is climbing in the east in the few hours before dawn, floating among the stars of Aquarius the Water-bearer. Saturn looms large in a telescope, stretching some 17″ across. Its rings are nearly edge-on, with just a bit of their northern side visible. That angle will continue to shrink a little by next month, then slightly grow again later this year before slimming once more as we approach the next ring-plane crossing in 2025.

If you’re able to catch the ringed world around 4:30 A.M. EDT (depending on your location and whether the planet has risen), you’ll notice that its largest moon, Titan, lies just northwest of the disk. Follow Saturn as the sky lightens (or as it rises, for time zones farther west) to see the moon closing in on the disk. Titan disappears behind Saturn in an occultation just after 5 A.M. CDT — note the disappearance is not visible in the Eastern time zone, where the Sun has already risen. The moon won’t reappear from behind the planet’s northeastern limb until just before 7 A.M. PDT, long after sunrise on the West Coast as well.

By tomorrow morning, Titan will have moved far beyond the planet, sitting roughly 1′ to its east. The moon will continue east until the 25th, when it will sit some 3′ from Saturn; after that, its orbit will begin carrying it back toward the ringed world.

Sunrise: 5:40 A.M.
Sunset: 8:14 P.M.
Moonrise: 6:42 P.M.
Moonset: 4:19 A.M.
Moon Phase: Waxing gibbous (96%)

Wednesday, May 22
Because we have a 2D view of the 3D sky, not all objects are as they seem. Take the double star 15 and 17 Canum Venaticorum, high overhead in the southwest a few hours after sunset tonight.

You’ll find this 6th-magnitude pair of stars some 2.8° due east of similarly bright 6th-magnitude Alpha (α) CVn. The two are just under 5′ apart and pretty close in magnitude (6.3 and 5.9 for 15 and 17, respectively). You may notice they look much like a wider version of Porrima in Virgo, which we observed earlier this week.

But you may be waiting for the catch, and here it is: These two stars are not in a binary system. In fact, they’re not close to each other at all! While 17 CVn is relatively close to Earth, at a distance of about 200 light-years, 15 CVn lies far beyond it, some 1,100 light-years away! The “pair” we see is merely a projection on the sky, as is the case with many stellar pairs visible in our skies.

Sunrise: 5:39 A.M.
Sunset: 8:15 P.M.
Moonrise: 7:49 P.M.
Moonset: 4:45 A.M.
Moon Phase: Waxing gibbous (99%)

Thursday, May 23
Full Moon occurs this morning 9:53 A.M. EDT. May’s Full Moon is also called the Flower Moon, and you’ll want to catch it later this evening when our satellite passes just 0.4° north of the brilliant red giant Antares at 11 P.M. EDT. The event is readily visible in the eastern half of the U.S., though those farther west may have to wait an hour or two for the pair to rise high enough in the sky for viewing.

If the Moon is above your horizon by 11 P.M. EDT, look southwest to spot it just below Antares, Scorpius’ 1st-magnitude alpha star. Plus, there’s a bonus — a second occultation for portions of the U.S. this week. Observers in the southeastern region of the country will now see the Moon occult Antares, passing in front of the star between about 9 P.M. and 10 P.M. EDT — again, check IOTA’s webpage for the event to see if your location falls within the viewing area and find out when you will see the star disappear and reappear.

Antares is a red giant in the later stages of its life — although it has swelled in size, its temperature has dropped, which is what gives the star its reddish hue. It’s so bright and so red that it is often mistaken for our own Red Planet, Mars. If you want to compare the two, you’ll need to wait several hours, until about 4:15 A.M. local daylight time tomorrow morning — that’s when Mars will rise more than 5° above the eastern horizon and you can see whether you think its brightness and hue match that of Antares, now in the southwest and well clear of the Moon!

Sunrise: 5:38 A.M.
Sunset: 8:16 P.M.
Moonrise: 8:57 P.M.
Moonset: 5:18 A.M.
Moon Phase: Full

Friday, May 24
Last night we viewed Antares, a red giant star in Scorpius. Tonight, let’s look at another particularly red star: Mu (μ) Cephei, also known as Herschel’s Garnet Star or simply the Garnet Star.

This 4th-magnitude sun is some 20° above the northern horizon shortly after 10 P.M. local daylight time tonight. Located in Cepheus the King, it lies south (to the lower right) of the more familiar house-shaped constellation outline, just below the halfway point on a line drawn between Zeta and Alpha Cep. You’ll immediately notice its ruby-red color. That color is a combination of the star’s cool temperature and what astronomers call reddening, as its light travels to us through interstellar dust within the Milky Way. Dust tends to preferentially scatter bluer light away, so we receive only the redder wavelengths of this star’s light, which already trends toward the red end of the spectrum due to its aging nature.

The Garnet star is one of the largest and most luminous stars in the sky. It sits more than 2,000 light-years from Earth. It is also a variable star with a period of some 800 to 1,000 days. Over this timeframe, its brightness can dip and rise again by about a magnitude — certainly noticeable to most observers!

Because it is such a massive star, Mu Cep will someday explode as a brilliant supernova.

Sunrise: 5:37 A.M.
Sunset: 8:17 P.M.
Moonrise: 10:03 P.M.
Moonset: 5:58 A.M.
Moon Phase: Waning gibbous (98%)

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