The two gas giants of the solar system, Jupiter and Saturn, are both accessible during late-evening hours during the latter half of the month. First comes Jupiter low in the east-southeast; Saturn will follow about two hours later. They will be drawing closer to each other between now and the end of next year, eventually leading to a historically close conjunction in December 2020.
Meanwhile, Mars is no longer a dazzling object, rather it's now a 2nd magnitude light scooting through the stars of Taurus and Gemini and along the way it will pass close to the beautiful star cluster M35 during the third week of May. Venus languishes all by its self in the dawn twilight, low near the eastern horizon less than hour before sunup. Finally, Mercury is pretty much out of the viewing loop for much of the month, although toward month's end you can glimpse it in the bright twilight sky with binoculars very low near the west-northwest horizon about 45 minutes after sundown.
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.
Planet Viewing Guide
Mercury – is wheeling around the far side of the sun, passing superior conjunction on May 21st, after having passed its ascending node on the 19th. Since it will also be at perihelion on the 24th, this speedy little planet will quickly enter the evening sky. By May 26th, Mercury sets about ¾ hour after sunset, and can be viewed with binoculars at magnitude -1.6 just above the west-northwest horizon. Look for it far to the lower left of the bright star Capella.
Venus – shining at magnitude –3.9, is the brightest planet as always, but in May it rises only one hour before the sun. You must look for it very low in the east about 45 to 30 minutes before sunup, but it is obvious to the unaided eye all month despite its modest altitude. Early on the morning of May 2nd, the very thin waning crescent moon, just 2½ days before new, sits about 5 degrees to the lower right of Venus. Binoculars will greatly assist you in making this sighting, especially considering how low to the eastern horizon our natural satellite will be and how bright the background twilight sky is.
Mars – having faded to magnitude +1.7, is now ranked among stars of second magnitude. It still shines with an orange-red hue, but that's about the only distinctive thing about it. It is hard to believe that this is the same object that last July and August blazed with such tremendous fiery brilliance that it was at one point the third brightest object in the night sky behind the moon and Venus. It starts the month setting nearly 3½ hours after sunset, but 2½ hours by month's end. It starts May between the horns of Taurus, and crosses over into Gemini on the 16th. On the evening of May 7th you'll see it 4 degrees to the upper right of the moon. And if you train binoculars on it centered for a few days around May 19th, you'll also see it passing near the big open star cluster M35 in Gemini. The 19th century British astronomer, William Lassell wrote: "It is a marvelously striking object. No one can see it for the first time without an exclamation."
Jupiter – blazing brilliantly at magnitude -2.6, in southern Ophiuchus rises around 11:30 p.m. daylight-saving time on May 1st but around a half-hour after sunset by month's end. Jupiter will reach opposition to the sun on June 10th, so it's already visible for most of the night and is essentially as large as it will appear this year. Jupiter is very far south, though, so even at its highest in the hours between midnight and dawn, its image may be less than crisp to northern telescope users. To Jupiter's southwest sparkles red Antares; the gap between them closes from 15 degrees to 12 degrees during May. Late on the night of May 19th, the moon forms a broad isosceles triangle with Jupiter and Antares with Jupiter situated about 8 degrees to the moon's lower left and Antares a similar distance to the moon's lower right.
Saturn – in Sagittarius finally becomes visible during evening hours this month. In early May the ringed planet rises a little after 1 a.m. local daylight time, but by the 31st it comes up about a half hour after the last glow of twilight fades out. Once up, however, Saturn gains altitude very slowly due to its southern declination. You'll have to wait another 2½ hours for it to climb just 20 degrees above the horizon if you live near 40 degrees north latitude. Saturn rises a little faster if you live south of there, slower if you are north. By the time it is 20 degrees up it has shifted to the southeast. Early on the morning of May 23rd, you'll find Saturn about 4 degrees to the upper right of the waning gibbous 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, and he is also an on-camera meteorologist for Verizon FiOS1 News in New York's lower Hudson Valley. Follow us on Twitter @Spacedotcom and on Facebook.