The next total eclipse of the Sun is almost two years away. But astronomers will watch many “total eclipses” between now and then. Known as occultations, they occur when one astronomical object passes in front of another, blocking the more distant one from view. The most frequent “blocker” is the Moon. And early tomorrow it’ll block out Spica, the brightest star of Virgo.

Spica is just two degrees from the ecliptic, which is the Sun’s path across the sky. The Moon moves five degrees to either side of the ecliptic, allowing it to cover the bright star. And they’re going through a series of occultations now. Tonight’s event is the last one visible from the United States this year.

Spica consists of two heavy stars that orbit each other once every four days. Occultations have helped astronomers decipher the system’s multiple personality, and learn some of its details.

The main star, Spica A, is more than 11 times the mass and seven times the diameter of the Sun. Because it’s so massive, within a few million years the star will blast itself to bits as a supernova. Spica B is no slouch, either. But it’s not quite heavy enough to become a supernova. Instead, it will cast its outer layers into space more gently, leaving behind a small, hot corpse.

Spica and the Moon climb into view just a couple of hours before dawn. The occultation will be visible across most of the country. The exact timing depends on your location.

Script by Damond Benningfield