What’s in the sky this month?

The innermost planets straddle nighttime, with Mercury in the evening and the greatest western elongation of Venus in the morning. Jupiter joins Mercury in early twilight for a few evenings, both setting quickly. Distant Mars lingers with Leo after dark, as our own planet hustles along its orbit well ahead of the Red Planet. Saturn is visible in the early hours, as Neptune hangs nearby and is in conjunction with the ringed planet on the 29th. Uranus reappears in the morning sky before dawn.

We’ll start in the evening soon after sunset on June 1. You can spot Jupiter hanging low in the western sky. It shines at magnitude –1.9 and becomes visible about 20 minutes after sunset, standing 8° high. Each day it becomes harder to see, but is joined June 6 to 9 by Mercury, which is slowly extending its elongation from the Sun.

Your first chance to spot Mercury is on June 6, when it shines at magnitude –1.5 and stands 3.7° west of Jupiter. The pair of bright planets sits about 3° above the western horizon 30 minutes after sunset. Your observing window is narrow because the planets set together within 25 minutes. Grab a pair of binoculars for the best view in bright twilight, which otherwise makes the two planets challenging to see. Make sure you pick a viewing site with no obstructions. The gap between the planets shrinks to 2.3° by June 7.

June 8 is their formal conjunction, when Mercury stands 2° due north of Jupiter. Jupiter is less than 3° above the horizon half an hour after sunset, while Mercury is 4° high. Mercury has dimmed slightly to magnitude –1.3.

Jupiter is lost from view soon after and heads toward its conjunction with the Sun on the 24th. It’ll reappear in the morning sky in late July. 

Meanwhile, Mercury continues to climb higher in the evening sky, though it dims as it goes. On the 13th, at magnitude –0.8, it stands 20′ from 3rd-magnitude Mebsuta (Epsilon [ε] Geminorum). Binoculars give a fine view of the star nestled next to the planet. Look 45 minutes after sunset, when the planet is 5° high in the west.

By June 24, Mercury has dipped to magnitude 0 and lies in line with Castor and Pollux, both 1st-magnitude stars. It sets about 90 minutes after sunset and stands 5° high at 9:30 p.m. local daylight time from latitudes similar to the U.S.

On the 26th, Mercury sits 3.5° to the left of the slender, two-day-old crescent Moon, and by the 30th it lies within 2.5° of M44, the Beehive star cluster. You’ll need binoculars — along with a clear western horizon and good air clarity — to spot the cluster.

It’s worth following Mercury with a telescope throughout June. Its disk is tiny, spanning a mere 5″ on the 6th, when it lies far beyond the Sun. As the month progresses, Mercury moves in its orbit, and by the end of June its disk has grown to 8″ across. During the same period, we see the phase change from a nearly full, 92-percent-lit disk on June 7 to 50 percent lit on the 28th. By June 30, it is a fat crescent, 46 percent lit.