Sky This Week is brought to you in part by Celestron.
Friday, May 9
Asteroid 9 Metis reaches at opposition at 2 A.M. EDT in the constellation Libra. The 10th-magnitude main-belt world is visible with binoculars or a telescope all night from sunset to sunrise. It stands highest around local midnight when it appears in the south, just 4.4° east-northeast of Zubenelgenubi, Libra’s alpha star.
Earlier in the evening, mighty Hercules dominates the eastern sky, reaching some 30° high around 10 P.M. local daylight time. Hercules hosts a well-known four-star asterism called the Keystone, which sometimes is drawn to depict the Strongman’s torso on the sky. It lies about halfway between the bright stars Vega in Lyra and Arcturus in Boötes, which you can connect with an imaginary diagonal line on the sky as you look east this evening. Halfway along that line is the Keystone.
At the Keystone’s southwestern corner is the brightest of its stars, Zeta (ζ) Herculis, which shines at magnitude 2.8. From this point, move about 7° north (to the upper left) to find magnitude 3.5 Eta (η) Her. Now slide 6.5° east (to the lower left) and locate magnitude 3.2 Pi (π) Her, then close out the Keystone by moving 6.5° southwest of Pi to land on magnitude 3.9 Epsilon (ε) Her.
Sunrise: 5:51 A.M.
Sunset: 8:03 P.M.
Moonrise: 5:30 P.M.
Moonset: 4:13 A.M.
Moon Phase: Waxing gibbous (92%)
*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 10
The Moon passes 0.4° south of Spica at 4 A.M. EDT. The best time for observing this pairing is in the few hours between midnight and 3 A.M. local daylight time, when they are still comfortably high above the horizon.
At that time, turn west to see the nearly Full Moon (now 95 percent lit) hanging just below Spica. The pair lies in southern Virgo the Maiden, the sky’s second-largest constellation after Hydra. Spica is a magnitude 1 star that helps to mark Virgo in the sky, as this constellation has few other bright suns to draw the eye. Some 250 light-years from Earth, Spica’s brilliance indicates it must be nearly 2,000 times as bright as our Sun for us to see it as a 1st-magnitude star.
Only the Moon’s far western limb remains in darkness as lunar day unfolds across ever more of the nearside. With a telescope, look along the terminator separating light from dark for a small but prominent circular crater in the lunar northwest, with its western interior wall brightly lit by sunlight. This is Aristarchus, which stretches about 25 miles (40 kilometers) wide and hosts a bright apron of ejecta around its rim.
The Moon reaches apogee at 8:47 P.M. EDT, when it sits at the farthest point from Earth in its roughly month-long orbit. At this time, our satellite will be 252,428 miles (406,243 km) away.
Sunrise: 5:50 A.M.
Sunset: 8:04 P.M.
Moonrise: 6:30 P.M.
Moonset: 4:33 A.M.
Moon Phase: Waxing gibbous (96%)
Sunday, May 11
The gas giant Jupiter still dominates the constellation Taurus as it sets in the west after sunset. Jupiter now stands just to the right of Alheka (Zeta Tauri), one of the tips of the Bull’s two horns. The magnitude –1.9 planet remains the brightest point of light in the constellation, making it easy to center in your telescope tonight.
While three of Jupiter’s four Galilean moons frequently pass in front of or behind Jupiter, the larger orbit of Callisto and the tilt of the gas giant’s equator relative to Earth mean that this moon often “misses” the planet from our point of view, passing far north or south of its poles.
Tonight, though, Callisto just grazes Jupiter’s northern limb from about 9 P.M. to 9:30 P.M. CDT as it passes from west to east. The moon is most directly north of the planet’s pole at about 9:20 P.M. CDT. Note that this event is best seen in the Central time zone of the U.S. — Jupiter is setting for East Coast observers at this time, while the sky is still quite light in the Mountain time zone, as it’s shortly after sunset in this region.
However, even those farther west will still get a bit of a show, as Io begins a transit from east to west across the disk of Jupiter at 9:07 P.M. MDT. Just a few minutes later, have your gaze locked on the region just off Jupiter’s northeastern limb, as Ganymede will suddenly pop into view, having crossed from west to east through Jupiter’s long, dark shadow.
The planet’s fourth Galilean moon, Europa, lies far west of the planet all night tonight.
Sunrise: 5:48 A.M.
Sunset: 8:05 P.M.
Moonrise: 7:32 P.M.
Moonset: 4:56 A.M.
Moon Phase: Waxing gibbous (99%)
Monday, May 12
Full Moon occurs at 12:56 P.M. EDT this afternoon. May’s Full Moon is also called the Flower Moon and because our satellite is still near apogee, it will appear some 29’ across, slightly smaller than the Full Moon’s average size (about 31’) in the sky.
The Full Moon rises roughly opposite the Sun, so Luna will emerge above the southwestern horizon shortly after sunset this evening. Our satellite is now in the constellation Libra, shining brightly just west (to the upper right as they rise) of the prominent claw of Scorpius the Scorpion. The Moon will pass close to the Scorpion’s heart, Antares, in just two days’ time.
Observing deep-sky objects during the Full Moon is challenging, but bright objects on the opposite side of the sky may still be reachable. Over in the west, Mars is still in central Cancer, so take a look at the Red Planet tonight, now nearly 4° east of the Beehive Cluster (M44), which it passed close by earlier this month. Mars shines at 1st magnitude, making it the brightest light in Cancer. M44, which can be visible to the naked eye under dark conditions, will likely be washed out by the light of the Moon and require binoculars or a telescope to enjoy this evening.
Other bright stars nearby that should be visible to the naked eye include magnitude 0.4 Procyon, below Cancer as this region sets, and Castor (magnitude 1.6) and Pollux (magnitude 1.2) in Gemini, to Mars’ lower right. To the far fight of Castor and Pollux is magnitude 0.1 Capella, the luminary of the large constellation Auriga.
Sunrise: 5:48 A.M.
Sunset: 8:06 P.M.
Moonrise: 8:35 P.M.
Moonset: 5:22 A.M.
Moon Phase: Full
Tuesday, May 13
Mercury is quickly dropping out of sight, so catch this early-morning planet while you still can. Today you’ll find the solar system’s smallest world just 3° high in the east 20 minutes before sunrise. Shining at magnitude –0.6, Mercury is readily visible, though not as eye-catchingly bright as blazing Venus (magnitude –4.6) some 26.5° to its upper right. First-magnitude Saturn, about 9.6° to Venus’ upper right, will likely be invisible in the brightening sky so soon before sunrise.
Through a telescope, Mercury’s disk appears nearly 80 percent lit, but it is also just 6” across. That’s because the tiny planet is approaching superior conjunction, when it sits on the opposite side of the Sun from Earth and our two planets are far apart. Mercury is now nearly 1.2 astronomical units from Earth, or 111.5 million miles (179.4 million km). One astronomical unit, or AU, is the average Earth-Sun distance of 93 million miles (150 million km).
As Mercury’s orbit carries it toward superior conjunction, the planet will appear to drop lower and lower in the sky, rising later and later (i.e., closer and closer to the Sun) each morning. It will soon be unobservable for a time, so get in your last looks now.
By contrast, Earth and Venus are currently quite close to each other in their orbits, so Venus’ disk appears large but less of it is illuminated. Your telescope will show that Venus is only a 38-percent-lit crescent, but its apparent angular size is now 30”.
Make sure to put away your telescope well before sunrise occurs from your observing location, which may differ from the time given below.
Sunrise: 5:47 A.M.
Sunset: 8:07 P.M.
Moonrise: 9:38 P.M.
Moonset: 5:54 A.M.
Moon Phase: Waning gibbous (99%)
Wednesday, May 14
The Moon passes 0.3° south of Antares in the constellation Scorpius at 1 A.M. EDT. The pair is high in the southern sky at this time, particularly for observers in the eastern half of the U.S., offering an excellent view. (Observers farther west will want to wait an additional hour or two for the region to rise higher in the sky as Earth rotates.) The two are so close they will just fit together in a wide-field telescope’s field, and appear comfortably within the same field of view of binoculars.
You’ll spot the Moon easily, still appearing nearly Full with 98 percent of its surface illuminated. Antares, shining at magnitude 1.1, is just above and slightly to the right of our satellite in the sky this morning. The bright red heart of the Scorpion is a well-known red supergiant star that weighs in at some 15 to 18 times the mass of our own Sun. Now in the later stages of its life, Antares has cooled but swelled up — if dropped into the center of our solar system, its surface would reach more than halfway out to the orbit of Jupiter. The star shows off a lovely orange-red hue through binoculars or a telescope, similar in color to the planet Mars.
Asteroid 3 Juno reaches opposition at 2 P.M. EDT in the constellation Serpens Caput. We’ll check out this main-belt world in tomorrow’s entry.
Sunrise: 5:46 A.M.
Sunset: 8:08 P.M.
Moonrise: 10:37 P.M.
Moonset: 6:32 A.M.
Moon Phase: Waning gibbous (96%)
Thursday, May 15
The main-belt asteroid 3 Juno is now at opposition, meaning it lies directly opposite the Sun in our sky, rising at sunset and setting at sunrise.
Two hours after sunset tonight, Juno is 30° high in the southeast. Glowing at magnitude 10, it’s within reach of binoculars or a small telescope. You can find Juno some 2.3° northwest of magnitude 3.5 Mu (μ) Serpentis, which lies at the far southern border of Serpens Caput near northeastern Libra. The third asteroid ever discovered, Juno is about 155 miles (250 km) across, making it the third-largest body in the main belt.
While you’ve got your optics out, slide your gaze a little over 7° northwest of Juno, or roughly 8.5° west-southwest of magnitude 3.7 Epsilon (ε) Ser. There you’ll land on globular cluster M5, which shines at magnitude 5.6 and covers roughly 23’ on the sky. This bright, dense globular has a tightly packed center but its outer regions resolve into several tens of stars under magnification. Astronomers believe it is one of the Milky Way’s oldest globular clusters, with an age of some 13 billion years.
Sunrise: 5:45 A.M.
Sunset: 8:09 P.M.
Moonrise: 11:32 P.M.
Moonset: 7:19 A.M.
Moon Phase: Waning gibbous (92%)
Friday, May 16
High in the southern sky around 10 P.M. local daylight time is the constellation Coma Berenices. Look for it to the upper right of the bright star Arcturus in Boötes and to the left of Denebola, the sun marking Leo the Lion’s tail.
Coma Berenices might be a relatively unobtrusive constellation, but it houses a spectacular cluster of distant galaxies, the Coma Cluster. In a 4° area of sky, you’ll find more than 1,000 galaxies, although Astronomy Associate Editor Michael Bakich suggests concentrating on the cluster’s inner 0.5°, where many stunning galaxies are packed in.
To locate the Coma Cluster, scan about 2.7° west of magnitude 4.2 Beta (β) Comae Berenices. The cluster’s brightest galaxy is magnitude 11.5 NGC 4884 (which is also cataloged as NGC 4889). Similarly bright magnitude 11.7 NGC 4874 lies just 7’ west of this galaxy; there are several smaller, fainter galaxies clustered around each of these larger galaxies. Also notably bright is magnitude 11.6 NGC 4793, which lies about 1.5° northwest of this pair.
Sunrise: 5:44 A.M.
Sunset: 8:10 P.M.
Moonrise: —
Moonset: 8:15 A.M.
Moon Phase: Waning gibbous (85%)
