The Sky This Week for May 16 to 21
The Summer Triangle, the Big Dipper, and other cool things to look for in the sky this week.
By Richard Talcott
Tuesday, May 16
Venus appears brilliant in the eastern sky from the time it rises around 4 a.m. local daylight time until close to sunrise nearly two hours later. It stands 10° above the horizon an hour before the Sun comes up. Shining at magnitude –4.6, it easily ranks as the night sky’s brightest light after the Moon. When viewed through a telescope this morning, Venus spans 30″ and appears about 40 percent lit.
Wednesday, May 17
Mercury reaches greatest elongation today, when it lies 26° west of the Sun and appears 4° above the eastern horizon 30 minutes before sunrise. To locate the innermost planet, scan the area to the lower left of Venus with binoculars. Mercury shines at magnitude 0.5 and should stand out with this optical aid, though you may have a hard time spying it against the twilight glow with your naked eye. Because the planet grows brighter during the next two weeks and doesn’t lose any altitude, you can follow it through the end of May.
Thursday, May 18
Last Quarter Moon occurs at 8:33 p.m. EDT. When it rises around 2 a.m. local daylight time tomorrow morning, it will appear a bit less than half-lit. Earth’s only natural satellite appears against the backdrop of Aquarius the Water-bearer.
Saturn starts today among the background stars of western Sagittarius but crosses the invisible border into Ophiuchus by day’s end. It will remain among the Serpent-bearer’s stars until November, when it moves back into Sagittarius.
Friday, May 19
The Big Dipper’s familiar shape lies nearly overhead on May evenings. The spring sky’s finest binocular double star marks the bend of the Dipper’s handle. Mizar shines at 2nd magnitude, some six times brighter than its 4th-magnitude companion, Alcor. Even though these two are not physically related, they make a fine sight through binoculars. (People with good eyesight often can split the pair without optical aid.) A small telescope reveals Mizar itself as double — and these components do orbit each other.
Saturday, May 20
Mars’ days as a prominent evening object are dwindling to a precious few. The Red Planet appears 10° high in the west-northwest 45 minutes after sunset and dips below the horizon shortly before 10 p.m. local daylight time. The magnitude 1.7 planet lies among the background stars of Taurus the Bull. Unfortunately, a telescope shows no detail on the ruddy world’s 4″-diameter disk.
Sunday, May 21
The sky’s brightest asteroid should be relatively easy to find through binoculars or a telescope this evening. Eighth-magnitude Vesta resides in the constellation Cancer the Crab just 3° north of the spectacular Beehive star cluster (M44). To confirm a sighting, sketch four or five stars in the field of view and then return to the same field a night or two later. Vesta will be the “star” that moved. And while you’re in the area, be sure to enjoy a view of the Beehive. You should be able to spot the cluster as a faint and fuzzy cloud with your naked eye. But M44 explodes into dozens of stars through binoculars or a small telescope at low power.