A gazelle leaps past the feet of the great bear. In ancient skylore, in fact, it made three leaps – each marked by a pair of stars.

The stars that mark the first jump are known as Alula Borealis and Alula Australis – the northern and southern first leaps. As night falls this evening, they’re high in the northwest. They’re far to the left of the Big Dipper, which has the most prominent stars of the great bear. The “alulas” are close together, so they resemble a pair of eyes.

Alula Australis holds an important distinction in the history of astronomy.

A telescope reveals it’s a “double” star – two stars that are close together. By measuring the motions of the stars, in the late 18th century, astronomer William Herschel showed that they’re bound to each other. That made the system the first confirmed binary – two stars that move through space together, tied by their mutual gravitational pull.

A few decades later, it became the first binary to have its orbit accurately measured. The stars orbit each other once every 60 years, at an average distance of more than 20 times the distance from Earth to the Sun.

In more modern times, astronomers found that both stars are binaries on their own – each has a small, faint companion in a tight orbit. So the first leap of the gazelle consists of at least four stars, leaping through the galaxy as a family.

We’ll talk about the second leap tomorrow.

Script by Damond Benningfield