According to NASA, multi-planet lineups are visible "every few years," but a seven-planet alignment is particularly uncommon, as each planet's orbit varies, with some moving more quickly and Mercury, in particular, being visible during its 88-day orbit for only "a couple of weeks at a time" each year.

Venus, Mars, Jupiter, Saturn, Uranus, and Neptune were already visible in the night sky after dusk this month, but Mercury joined them on Feb. 28. While it's common to see a few planets line up in the night sky, four or more is a treat, according to NASA.