All five of the planets that are easily visible to the unaided eye put in good appearances this month. Venus reigns as the brilliant Morning Star, while slightly fainter Jupiter sparkles from late evening until dawn. Mars inches farther from the Sun in the morning sky, as does golden Saturn. Mercury does double duty: It is low in the southwestern evening sky as the month begins, then climbs low into the southeast at dawn by month’s end.
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In the Sky This Month
April 30: Alphecca
Corona Borealis, the northern crown, is a pretty semicircle of stars that’s about a third of the way up the eastern sky at nightfall. Its brightest star, Alphecca, is at the center of the semicircle.
May 1: Beltane
In the calendars of ancient Ireland and Scotland, May 1 was Beltane, a day dedicated to celebrating the end of winter and the start of summer. Beltane is a “cross-quarter” day, which comes roughly half-way between a solstice and an equinox.
May 2: Disappearing Sirius
Sirius, the brightest star in the night sky, is disappearing in the evening twilight. Look for the star blazing low in the southwest beginning in early twilight. It sets a couple of hours after sunset.
May 3: Evening Mars
Mars is pushing into the pre-midnight sky, getting brighter as it does so. Tonight, look for the orange planet quite low in the southeast by 11 or 11:30 p.m. The star Antares is close below Mars, with the planet Saturn farther to the lower left of Mars.
May 4: Mu Herculis
Like its constellation, Hercules, the star Mu Herculis is faint and difficult to find. Yet the star is of particular interest because in some ways it seems to be an older version of the Sun, so it’s had plenty of time to give rise to life.
May 5: Head Cases
The star Rasalhague represents the head of Ophiuchus, the serpent bearer, while Rasalgethi is the head of Hercules. Rasalhague climbs into good view in the east by 10:30 p.m., with fainter Rasalgethi above it. They are separated by about the width of three fingers held at arm’s length.
May 6: Mercury Transit
A tiny black dot will cross the face of the Sun early Monday: Mercury, the Sun’s closest planet. The entire event, known as a transit, will be visible across the eastern half of the United States, with the rest of the country seeing most of it.