The most important thing to know about a star is its mass – how heavy it is. Among other things, the mass reveals how long the star will live and how it will die. Measuring the mass of a single star is tough. It’s a lot easier to get the masses of stars in binary systems – two stars that orbit each other.

An example is Menkalinan, the second-brightest star of Auriga. It’s a third of the way up the northeastern sky at nightfall, below the charioteer’s brightest star, Capella.

Menkalinan’s two stars are so close together that we can’t see them as individual points. But breaking the system’s light apart reveals the presence of both stars.

The stars orbit each other every four days, at about one-tenth of the distance from Earth to the Sun. Combined, those numbers reveal the system’s total mass.

A couple of other numbers complete the picture. One is the angle at which we’re seeing the system. In the case of Menkalinan, that’s easy – the stars pass in front of each other, so we see the system edge-on. The other is the orbital motions of the stars. Plugging those numbers into the formula provides a precise mass for the individual stars.

The stars of Menkalinan are almost identical. Each is more than twice the mass of the Sun. Each is also bigger and brighter than the Sun. So even though Menkalinan is more than 80 light-years away, it’s easy to see – the combined glow of two big, well-understood stars.

Script by Damond Benningfield