As was the case in April, four of the five brightest planets are visible solely in the morning sky. Venus and Jupiter, coming off of a tight conjunction with each other on the final day of April, now begin to part ways in May. Still spectacularly close to each other at the start of the month, these two dazzlers will be nearly 30 degrees apart by the month's end.
Jupiter will climb higher each morning, reaching much fainter Mars by the 29th. Meanwhile, Mars provides an opportunity to make a sighting (with good binoculars and telescopes) of the most distant planet — Neptune — on the 18th, with Mars passing just to the south of this bluish gas giant. Saturn is also a morning object, positioned far to the west of Venus, Jupiter and Mars.
In the evening sky, there is only Mercury, shining low in the west-northwest sky right after sundown and keeping company with the nearby Pleiades star cluster, first-magnitude Aldebaran and, on the 2nd, a very thin crescent moon. Look quick, however, because Mercury will rapidly fade during the first week of May, then vanish. When you see it again next month, it will have joined the other four planets in the early morning sky.
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In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm's length measures roughly 10-degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Mercury
Mercury starts off the month setting in the west-northwest in a dark sky just a few minutes after the end of evening twilight. On May 1st, it shines at magnitude +0.7, just a bit brighter than orange Aldebaran and is easily found a dozen degrees to the lower right of that star. Additionally, binoculars or a wide-field telescope will reveal the pretty sight of the Pleiades centered only about 2 degrees to the right of this speedy planet.
On the following evening, the slender sliver of the two-day-old moon (4% illuminated) will join the array, sitting 4 degrees to Mercury's upper left. Telescopically, the planet appears about one-fourth illuminated and in the days that follow, as its crescent phase thins, Mercury rapidly fades to magnitude +1.6 by the 6th; a couple of nights later the planet can no longer be seen.
Mercury passes through inferior conjunction between the sun and Earth on the 22nd and enters the morning sky.
Venus and Jupiter
Venus and Jupiter pick up where they left off at the end of April, continuing to call attention to themselves as May opens, mimicking a dazzling "double planet" low in the eastern dawn sky. The two planets rise around the beginning of dawn (for skywatchers at mid-northern latitudes) and will be about 12 degrees high in the east roughly a half-hour before sunrise. In the mornings that follow, Jupiter will pull away from Venus, ascending toward the west, and by month's end the big planet will be coming up at about 2:30 a.m. daylight-saving time. Venus, meanwhile, will continue to rise as dawn breaks, all the way through August.
On the 25th, the moon will sit about 5 degrees to the lower left of Jupiter, and Jupiter in turn will be 2.5 degrees to the left (east) of Mars. On the 27th, the crescent moon will be 3.5 degrees to the lower left of Venus. Finally, on the morning of the 29th, Mars and Jupiter are in conjunction with Mars passing only 0.6 degrees below Jupiter.
Mars
Mars rises about 30 minutes before the first light of dawn in May, as it has done every morning since the beginning of the year. Mars has doubled in brightness since then, however, and has traveled eastward from Ophiuchus through Sagittarius and Capricornus into Aquarius. But the red planet still isn't much to look at through a telescope. It's a gibbous ball that even in moderately large telescopes appears as nothing more than an orange speck.
But also on May 18th, the red planet will be passing 0.5 degrees south of Neptune, providing a good opportunity to identify this most distant planet. With large binoculars or a telescope, Neptune will appear as a tiny bluish "star" only about 1/700 as bright as Mars. As noted above, Mars will have a close rendezvous with Jupiter in the predawn hours of the 29th.
Saturn
Saturn through this month glows in the southeast in eastern Capricornus as dawn starts. On May 22nd, during the wee hours of the morning, you'll see Saturn shining like a bright yellow-white "star" hovering 5 degrees above the last quarter moon.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.
