Mizar

The bend of the Big Dipper's handle — with a faint partner, Alcor.

Good eyes can see a faint star, Alcor, right next to Mizar. Being able to split them was an old eyesight test.

Understand it

A star's colour tells its temperature: blue stars are hottest, red ones coolest.

The distance light travels in a year: about 9.5 trillion km.