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Moon and Regulus

November 25, 2021

Regulus, the star at the heart of the lion, has a small, faint companion. Astronomers have known about it for a while, but they’ve never seen it. In fact, they’ve had a hard time figuring out its details.

That’s because the two stars are quite close together, and because Regulus itself is far brighter than the companion. So trying to see the other star is like trying to pick out a flashlight right next to a searchlight.

Astronomers discovered the companion by breaking the light from Regulus into its individual wavelengths or colors. Patterns in that rainbow of colors reveal details about Regulus. Detailed observations reveal a second pattern mingling with the first — the imprint of the companion.

A study last year got the best look yet at that second imprint, allowing astronomers to nail down some of the companion’s details. It’s about a third the mass of the Sun, compared to almost four times the Sun’s mass for Regulus. Its surface is thousands of degrees hotter than the Sun’s. And it’s about six percent the Sun’s diameter.

The star is becoming a white dwarf — the final stage of life for a Sun-like star. Eventually, the star will get even smaller, and a bit cooler. That’ll make it even harder to see through the glare of brilliant Regulus.

Look for Regulus near the Moon the next couple of nights. It rises below the Moon late tonight, and stands to the lower left of the Moon at first light. It’ll be even closer to the Moon tomorrow night.

Script by Damond Benningfield

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