The Sky This Week: May 7 – May 15
A New Moon rises, Comet PANSTARRS makes an appearance, and Mercury crosses in front of the Sun.
Saturday, May 7
With an age of 4.5 billion years, “young” might not seem an appropriate word to describe our Moon. But tonight, you have an exceptional opportunity to see what astronomers call a “young Moon” — a slender crescent visible low in the west some 30 to 45 minutes after sunset. With New Moon having occurred yesterday afternoon, only 2 percent of our satellite’s disk appears illuminated this evening. You should notice an ashen light faintly illuminating the Moon’s dark side. This is “earthshine,” sunlight reflected by Earth that reaches the Moon and then reflects back to our waiting eyes. Use binoculars for the best view. The young Moon will be much easier to see tomorrow evening, when it appears significantly higher and some 7 percent illuminated.
Sunday, May 8
Although the Eta Aquariid meteor shower reached its peak last week (on May 5), it still should put on a show during the predawn hours for the next few nights. According to the International Meteor Organization, the shower’s broad maximum produces up to half the peak rate between May 3 and 10. Eta Aquariid meteors derive from debris ejected by Comet 1P/Halley during its many trips around the Sun. When Earth crosses this debris stream, our planet’s atmosphere incinerates the tiny dust particles and we see the streaks of light called meteors, or “shooting stars.” With the Moon now out of the sky, an observer at a dark site can expect to see 10 to 15 meteors per hour shortly before morning twilight begins. Those living close to the equator and in the Southern Hemisphere should have the best views.
Monday, May 9
Mercury passes directly between the Sun and Earth today for the first time since November 8, 2006. The innermost planet’s dark disk will transit the Sun’s face for 7.5 hours. Observers across most of the world (excluding Australia, New Zealand, eastern Asia, and the adjacent oceans) can view at least some of the transit. This is a morning event for most North Americans. Mercury first touches the solar disk at 7:12 a.m. EDT, lies closest to the Sun’s center at 10:57 a.m., and leaves our star’s limb at 2:39 p.m. You’ll need a telescope equipped with a safe, full-aperture solar filter to see this event. For complete observing details, see “How to view Mercury’s rare transit” in the May issue of Astronomy.
Tuesday, May 10
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.
Wednesday, May 11
Another comet in the growing throng of such objects discovered by the Pan-STARRS telescope in Hawaii makes its appearance it May’s morning sky. Comet PANSTARRS (C/2013 X1) currently glows between 7th and 8th magnitude in northeastern Aquarius. (This morning, it lies 2° northeast of 4th-magnitude Phi [f] Aquarii.) From most of the United States, you’ll need a clear, flat eastern horizon to spot the comet through a telescope just before dawn breaks.
Thursday, May 12
Brilliant Jupiter appears high in the south as darkness falls and remains on display until 3 a.m. local daylight time. The giant planet shines at magnitude –2.2 — brighter than any other point of light in the night sky — against the backdrop of southern Leo the Lion. Jupiter appears equally dazzling through a telescope, which reveals a wealth of atmospheric detail on a disk that spans 40″. Look carefully tonight and you should see a black dot crossing the cloud tops. This is the shadow of Ganymede, Jupiter’s (and the solar system’s) largest moon. This shadow transit takes place from 11:40 p.m. to 2:51 a.m. EDT.
Friday, May 13
First Quarter Moon occurs at 1:02 p.m. EDT. The half-lit orb rises just after noon local daylight time, appears highest in the south shortly before sunset, and sets around 2 a.m. The Moon spends this evening among the background stars of southwestern Leo the Lion, less than 5° from that constellation’s brightest star, Regulus.
Saturday, May 14
The Moon moves approximately 13° eastward relative to the starry background every 24 hours, and its motion carries it near Jupiter this evening. From North America, the two appear within 5° of each other all night. They will be in conjunction at 6 a.m. EDT tomorrow morning, when our satellite passes 2° due south of the planet.
Sunday, May 15
About 45 minutes after Mars rises, Saturn pokes above the southeastern horizon. Although the ringed planet pales in comparison to its neighbor, its yellow color contrasts nicely with the Red Planet’s hue. Throw in the ruddy glow of nearby Antares, the 1st-magnitude luminary of Scorpius, and you have a colorful trio of bright objects to follow throughout the late evening and morning hours. As you might guess, Saturn’s proximity to Mars means it also will reach opposition and peak visibility soon — in fact, it reaches this orbital highlight June 3. The view of Saturn through a telescope never fails to impress. This week, the world appears 18″ across and sports a beautiful ring system that spans 42″ and tilts 26° to our line of sight.
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