Cicadas aren’t the only scientific rarity expected this month. At the end of May three planets will be visible to the naked eye in one small area of the sky. The planets Mercury, Venus and Jupiter will form “the tightest gathering of three naked-eye planets that the world will see until 2026,” according to the venerable Sky & Telescope magazine.
“Add the Earth under your feet, and you're seeing half of the solar system's planets at once,” Sky & Telescope senior editor Alan MacRobert said in a prepared statement.
For viewers in the northern midlatitudes (including the U.S. and most of Europe), the best place to look for the trio is “in the western twilight about half an hour after sunset Saturday [see diagram above] and for a few days after,” according to StarDate, a magazine published by The University of Texas at Austin’s McDonald Observatory. The three planets will draw into closest alignment on the evenings of May 25 and 26 [see orbital diagram below]. Tiny Mercury, which orbits close to the sun, is usually much harder to spot than Venus and Jupiter, “but its proximity to them will make it stand out,” StarDate predicts.
The near-alignment of three planets is indeed unusual, but it is only a warmup for an even rarer celestial event in 2040. In September of that year, all five bright planets—Mercury, Venus, Mars, Jupiter and Saturn—will cluster in the evening sky.