Sky This Week is brought to you in part by Celestron.
Friday, May 16
Spring is a great time to observe star clusters, so tonight our target is the globular M68 in Hydra.
Look south after sunset and you’ll find the eastern end of the Water Snake just below Virgo and Corvus. M68 is a relatively bright magnitude 7.8 cluster located just 3.5° southeast of magnitude 2.7 Beta (β) Corvi. The cluster is roughly 20° high around 10 P.M. local daylight time.
M68 spans about 11’ on the sky, making it moderately compact. This ancient grouping of suns is some 33,000 light-years away, which translates to a physical size spanning 106 light-years. M68 is a great small telescope target easily accessible to beginners, showing off numerous stars even at low magnification. Larger scopes and higher magnification will show not only the cluster’s slightly offset, out-of-round core, but a smattering of fainter background stars as well.
Sunrise: 5:44 A.M.
Sunset: 8:10 P.M.
Moonrise: —
Moonset: 8:15 A.M.
Moon Phase: Waning gibbous (85%)
*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 17
Uranus is in conjunction with the Sun at 8 P.M. EDT, meaning it lies on the opposite side of our star from Earth. It will return to our skies in June as a morning planet.
Still visible for some five hours after sunset is Mars, making its way through Cancer. Shining at 1st magnitude, this ruddy point of light is easy to find in the western sky during May evenings, standing directly above the bright star Procyon in Canis Minor as these constellations set.
Through a telescope, Mars’ disk spans just 6” — a reflection of its distance from Earth, now nearly 1.6 astronomical units (1 astronomical unit, or AU, is the average Earth-Sun distance of 93 million miles [150 million kilometers). Mars was last closest to Earth in January and has been trailing behind us in its larger orbit — and shrinking in our sky — ever since. Although surface features are now hard to make out for all but the most experienced imagers with the biggest scopes, anyone can enjoy the eponymous hue of the Red Planet in the sky, with or without optical aid.
With the Moon gone from the evening sky, you can also enjoy the Beehive Cluster (M44) in central Cancer, which Mars passed earlier in the month. Shining at magnitude 3.7 and spanning almost 100’, this large, bright open cluster is visible to the naked eye from a dark site and pops right out against the background when viewed with binoculars or any telescope.
Sunrise: 5:43 A.M.
Sunset: 8:11 P.M.
Moonrise: 12:19 A.M.
Moonset: 9:18 A.M.
Moon Phase: Waning gibbous (78%)
Sunday, May 18
The Moon passes 0.4° south of the dwarf planet Pluto at 8 A.M. EDT. Both are now in Capricornus, although the bright Moon will make viewing the dim, distant planet a challenge in the predawn sky.
In the evening sky, however, the bright beacon of Jupiter stands 2° due north of Zeta (ζ) Tauri. Look west and hour after sunset to find the magnitude –1.9 gas giant still 11° high. Zeta Tau, which shines at magnitude 3, lies to the planet’s lower left. Near this pairing is the location of M1, the Crab Nebula, but this supernova remnant is likely too challenging to view thanks to its faintness combined with the low altitude of this region at this time.
If you crave some deep-sky observing, opt instead for M35, an open cluster near the feet of Gemini, to Jupiter’s upper left. Located just 2.3° north-northwest of magnitude 3.3 Eta (η) Geminorum, M35 shines at magnitude 5.3 and spans roughly the same size on the sky as the Full Moon. Pull out binoculars or any small scope to enjoy this young grouping of several hundred stars, though you’ll want to catch them early, as the region sets less than three hours after the Sun.
Sunrise: 5:42 A.M.
Sunset: 8:12 P.M.
Moonrise: 12:58 A.M.
Moonset: 10:25 A.M.
Moon Phase: Waning gibbous (69%)
Monday, May 19
An hour after sunset, you’ll find the constellation Leo the Lion pointing head-down toward the horizon in the southwest. The brightest star in this constellation is Alpha (α) Leonis, also known as Regulus. And just over 5° west of this star is a sun called R Leonis, the first variable star identified in the Lion.
R Leonis shines with a noticeably red hue, thanks to its advanced age and thus cooler temperature. It is a Mira-type variable, a class of variable stars named after Mira in Cetus, the first such star of this type ever identified.
Discovered in 1782, astronomers estimate R Leo is less than 300 light-years away. This aging star undergoes huge brightness changes, swinging between magnitude 5 and 10.5 over the course of nearly a year (312 days). It has most recently been observed near the faint end of its range, roughly 9th magnitude, meaning you will need binoculars or a telescope to find it. One of the easiest ways to identify it is to look for a deep red star forming one point of a triangle with a pair of yellower stars.
R Leo is now approaching its faintest, which means in a few months it will begin brightening again. So, make note of its location and brightness now, to compare with your observations when Leo becomes a morning constellation rising in the east before the Sun in the fall.
Sunrise: 5:41 A.M.
Sunset: 8:12 P.M.
Moonrise: 1:31 A.M.
Moonset: 11:35 A.M.
Moon Phase: Waning gibbous (59%)
Tuesday, May 20
Last Quarter Moon occurs at 7:59 A.M. EDT. This phase of the Moon offers observers a chance to focus on our satellite’s western limb, including the huge, dark Ocean of Storms that stretches more than 1,600 miles (2,500 km) and is prominent in the lunar southwest.
A much smaller but nonetheless noticeable dark feature southwest of the Ocean of Storms and near the western limb is the crater Grimaldi. Stretching nearly 140 miles (122 km) across, Grimaldi’s smooth, flat floor lies above a so-called mascon, or concentration of mass beneath the lunar surface, of the sort often found beneath its larger, lava-covered maria. Use a telescope to scan the crater’s floor and look for subtle features such as mounds and ridges, which can be a fun challenge to pick out through the eyepiece.
Not far south of Grimaldi is a crater that appears its opposite: the bright, rayed crater Byrgius. A much smaller 54 miles (87 km) across, Byrgius’ floor is pocked with numerous small craters. The bright ray system actually emanates from Byrgius A, a smaller crater overlapping the larger main Byrgius’ rim, indicating the former came much later in cosmic time.
Sunrise: 5:40 A.M.
Sunset: 8:13 P.M.
Moonrise: 1:59 A.M.
Moonset: 12:45 P.M.
Moon Phase: Waning crescent (48%)
Wednesday, May 21
Virgo the Maiden is draped across the southern sky late this evening, offering excellent views of a famous galaxy within its bounds: M104, also known as the Sombrero Galaxy.
Glowing at magnitude 8, this edge-on spiral is some 30 million light-years from Earth. It boasts a thin, dark dust lane that blocks light across its center, which has earned it the name Sombrero. This structure is best seen with a telescope, although the galaxy is bright enough to pick up as an oval-shaped glow even in binoculars. M104 is roughly twice as wide as it is thick, spanning 9’ by 4’.
The Sombrero lies near the border of Virgo and Corvus, a smaller constellation nestled just south of the Maiden. To locate the Sombrero, start at 1st-magnitude Spica, Virgo’s alpha star. Move about 11° due west and you’ll land right on this celestial hat. Alternatively, you’ll also find the Sombrero by moving 5.5° northeast of closer but fainter 3rd-magnitude Delta (δ) Corvi.
Sunrise: 5:40 A.M.
Sunset: 8:14 P.M.
Moonrise: 2:24 A.M.
Moonset: 1:56 P.M.
Moon Phase: Waning crescent (37%)
Thursday, May 22
The Moon hangs near Saturn and Neptune in the early-morning sky, and it’s best to catch them earlier rather than later. Try looking east 90 minutes before sunrise, where you’ll easily spot the crescent Moon in southwestern Pisces, below the Circlet asterism.
Just to the lower left of the Moon is 1st-magnitude Saturn, which stands out well in a region with few bright stars. Through a telescope, Saturn’s disk stretches 17”, while its rings — with their southern face now just visible, tilted less than 3° — span 37”. Titan, the ringed planet’s largest and brightest moon, lies about 1.3’ due west of Saturn this morning and should also be visible in your eyepiece.
Now, scan 2° northeast of Saturn — directly to the left on the sky — to find distant Neptune. The ice giant shines at 8th magnitude and spans just 2”, so it will look like a “flat,” dim star that may have a grayish or bluish cast.
Far to the trio’s lower left and still close to the horizon an hour and a half before sunrise is blazing Venus, shining at magnitude –4.5. We’ll check out this planet tomorrow morning, when the Moon has drawn closer for another lovely pairing.
The Moon will pass 3° north of Saturn at 2 P.M. EDT, then passes 2° north of Neptune at 5 P.M. EDT.
Sunrise: 5:39 A.M.
Sunset: 8:15 P.M.
Moonrise: 2:48 A.M.
Moonset: 3:09 P.M.
Moon Phase: Waning crescent (26%)
Friday, May 23
Let’s return to the morning sky, where the Moon is now situated between magnitude 1.1 Saturn and magnitude –4.5 Venus in the east an hour before dawn.
If you were outside yesterday morning, you’ll note that the Moon is now a thinner crescent as it wanes toward New. Only its western limb is directly sunlit. But look for earthshine lighting up its shadowed face, as sunlight bounces off Earth to illuminate regions of the Moon already experiencing night.
Although Venus is unmissable even with the naked eye, use a telescope to observe it in more detail. The planet’s disk also appears as a crescent, now some 45 percent lit. That disk spans an impressive 26” in the sky, thanks to Venus’ proximity to Earth: It is currently just less than 5.9 million miles (9.4 billion km) from our planet, as our two worlds lie close to each other in their orbits around the Sun at this time.
The Moon will pass 4° north of Venus at 8 P.M. EDT tonight.
Sunrise: 5:38 A.M.
Sunset: 8:16 P.M.
Moonrise: 3:12 A.M.
Moonset: 4:23 P.M.
Moon Phase: Waning crescent (17%)
