Double Duty

StarDate

On modern maps of the universe, every star belongs to a single constellation. But in ages past, some stars were known as connecting stars – they belonged to two constellations. And one of those stars is close to the Moon early tomorrow.

The star is Elnath. Its name means “the butting one” – a reference to its position at the tip of one of the horns of Taurus, the bull. In fact, a second name for the star is Beta Tauri – an indication that it’s the second-brightest star in the constellation.

But until almost a century ago, Elnath was also known as Gamma Aurigae. That name indicated that it was one of the brighter stars of Auriga the charioteer. And in many older star atlases, it’s depicted as part of the charioteer’s outline.

Until the early 20th century, there were no rules about where a star might belong – it could be a member of more than one constellation with no problem. In the 1920s, though, the International Astronomical Union tidied up the geography of the heavens. It designated 88 official constellations. And it defined precise boundaries for each one. So every star was given its own home in the cosmos – including Elnath, the horn of the bull.

Elnath stands close to the Moon at dawn. Three other bright lights form a triangle to the upper right of the Moon: Mars, at the top of the triangle; brilliant Jupiter, at the lower left; and Aldebaran, the bull’s eye, at the lower right.

Script by Damond Benningfield