As the May nights begin to warm, the two inner planets share the limelight at dusk, the two Solar System giants hold hands, and a tiny red dot grows ever larger in the middle of the night.
The Shepherd’s Star and Mercury share the twilight sky
Since December, skywatchers have become accustomed to seeing a brilliant object blazing above the horizon in the western evening sky. The planet Venus, poetically but misleadingly christened the Shepherd’s Star, will continue to reign as the Evening Star for another month. Still near maximum brightness in early May, Venus gradually grows dimmer but mainly loses height above the west-northwestern horizon at dusk before disappearing in the Sun’s glare by late May. At the start of summer, Venus will serve as a guide to shepherds taking their sheep out to graze in the mornings.
Mercury, the other inner planet in our Solar System, will also grace the twilight sky this month, but spotting it will prove more challenging since it never rises more than a few degrees above the horizon. May 10 marks the start of a great “window of opportunity” for viewing Mercury as it heads toward greatest eastern elongation on June 4. Look for this tiny coppery-pink dot above the west-northwestern horizon 30 to 45 minutes after sunset. It shines more brightly at the beginning of the viewing window, with optimal conditions starting on May 15 when Mercury creeps upward over the horizon.
To help locate the planet, just scan the sky for the obvious guideposts. Low on the horizon on May 21 and 22, Venus brushes past Mercury, with about 1½ degrees of separation. Then on May 23 and 24, the close-knit inner planets are joined by a thin crescent Moon. Observing this conjunction on the 23rd will be a challenge as you’ll need a perfectly clear view of the horizon to spot the very thin crescent hanging 5 degrees beneath the planetary duo. The 24th will offer a better viewing experience with the Moon shining 5½ degrees to the left of Mercury and slightly higher above the horizon.
A pair of giants
After Venus and Mercury call it a night, there won’t be much planetary activity for the rest of the evening. But at around 2 a.m. in early May, and increasingly earlier until half past midnight by month’s end, an intriguing duo make an appearance in the southeast. Set against the starry background, these two points—one as a brilliant, steady and whitish light and the other as a more discreet, yellowish glow—are none other than the giant planets Jupiter and Saturn! The pair will grace our skies throughout the remainder of the night, culminating almost due south at the crack of dawn. On the morning of May 12, the waning gibbous Moon passes just 3 degrees south of Jupiter and completes a triangle that is clearly visible in the south-southeast at the end of the night and at dawn. On the morning of May 13, the Moon glides 7 degrees to the left of Saturn, again forming a nice conjunction.
The red wanderer
In the latter part of the night, a dot of orange light makes its appearance above the east-southeastern horizon. But at the beginning of the month, you’ll have to wait until 3 a.m. to see it, then increasingly earlier with each passing night. Although still fairly inconspicuous, the dot nonetheless pops out against the faint background stars. This celestial object, which wanders into Capricorn the first week of May before dashing through the stars of Aquarius, is the planet Mars. While it reaches opposition only on October 13, it can already be spotted. As the planet gradually approaches Earth this spring, it becomes increasingly radiant and brightens beyond zero magnitude on May 30. At the end of the night and at dawn on May 14, the last quarter Moon slips between Mars and the Saturn-Jupiter duo. The next morning, on May 15, the lunar crescent can be found a mere 4 degrees to the lower left of Mars. The best time to observe this encounter is around 4 a.m., when the pair is high enough above the southeastern horizon (about fifteen degrees) but before the modestly bright Red Planet gets washed out by dawn’s early light.