Stargazers of Arizona, keep your eyes skyward on early Saturday evening for a cosmic spectacle. A rare six-planet alignment will occur on Feb. 28 as Mercury, Venus, Saturn, Jupiter, Uranus and Neptune gather in a loose formation overhead. Astronomers call it a “planet parade,” and it’s one of the more striking celestial sights of the year.

A rare alignment of two exoplanets with their star, marking one of the few known exosyzygies, an astronomical event involving celestial bodies outside our solar system, is expected to occur. Despite its rarity, the phenomenon may pass entirely unobserved ...