For those who like to hunt for treasure, May offers nice views of the solar system’s most elusive naked-eye planet. Mercury appears as a pale-yellow dot low in the west-northwest during evening twilight starting at the end of May’s first week and continuing through the end of the month.
Although Mercury shines brightly, it can be hard to pick out against the twilight glow. Fortunately, the planet Jupiter serves as a guide. Jupiter shines brighter than any other point of light in the evening sky. Head outside about 30 minutes after sunset, and the brilliant planet will dazzle your eye from its perch high in the west.
Once you find Jupiter, look to the lower right in the direction where twilight appears brightest. Although Jupiter shines roughly five times brighter than Mercury, you should be able to spot the dimmer planet without much difficulty. According to Astronomy magazine Senior Editor Michael Bakich, “If you don’t see Mercury right away, try finding it with binoculars. Once you know where it is, Mercury will pop into view.”
Mercury reaches the peak of this evening appearance May 24 when it lies farthest from the Sun and climbs highest in the twilight sky. It then appears about 10° — the approximate angle covered by your closed fist held at arm’s length — above the horizon 45 minutes after the Sun sets. Mercury remains near this altitude from mid-May until the end of the month. Be sure to look the evening of the 30th when a thin crescent Moon hangs about 5° to the planet’s left.
Once you spot Mercury, you may wonder why it has a reputation for being elusive. It is, after all, one of the brightest objects in the sky. Unfortunately, this bright light never climbs high. Mercury orbits closer to the Sun than any other planet, so, from our perspective on Earth, it never strays far from our star’s glare. Even at its best, the innermost planet lies low in the west shortly after sunset or low in the east before sunrise. It never gets far enough from the Sun to appear high in a totally dark sky.
The great astronomer Nicolas Copernicus — the man who put the Sun in its proper place at the center of the solar system, with Earth circling it — reputedly never glimpsed Mercury. So take a few minutes one of these early March evenings to catch a sight few people ever have.
- Mercury orbits the Sun at an average distance of 36 million miles (58 million kilometers) but covers a broad range from 29 million miles to 44 million miles (46 million km to 70 million km).
- Mercury takes just 88 days to complete one orbit of the Sun.
- Mercury takes 59 days to rotate once on its axis.
- With a diameter of 3,032 miles (4,879 km, or 38 percent of Earth’s), Mercury is the smallest planet in the solar system.
- As you gaze at Mercury from afar, NASA’s MESSENGER spacecraft studies the planet from orbit. The probe has been circling Mercury since 2011, examining its surface, analyzing its interior, and measuring its magnetic field.