Most of the stars aren’t alone. But it can be tough to tell which stars have companions. The stars can be so close together that their light blurs into a single point. Or they can be so far apart that it’s hard to confirm that they’re actually bound to each other.

Examples of both can be found in a single star system.

Capella is one of the brightest stars in the night sky. Tonight, it climbs into view in the northeast in mid-evening, far to the left of the Moon.

Capella consists of two pairs of stars that are a trillion miles apart. One pair is quite bright — it forms the pinpoint we see with our eyes alone. The other is too faint to see without a telescope.

The stars that make up the bright pair are separated by about the gap between the Sun and Venus, the second planet out. From our distance of 42 light-years, it takes special telescopes to see the individual stars.

Astronomers discovered their binary nature by breaking their light into its individual wavelengths. That revealed two patterns of light — one for each star. Both stars are bigger, brighter, and heavier than the Sun.

The other pair consists of two faint stellar embers. They’re as far apart as Pluto is from the Sun, so it takes hundreds of years for them to orbit each other. As a result, it took decades to confirm that the stars form a binary. Today, we still haven’t seen them complete even a single orbit. So there’s a bit of uncertainty in the numbers about this faint pair of stars.

Script by Damond Benningfield

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