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Perhaps the most important number that astronomers need to know about a star is its distance. That allows them to calculate the star’s true brightness, which helps them calculate the star’s mass, its stage in life, and much more.

An example is Arneb, the brightest star of Lepus, the rabbit. At nightfall, the constellation stands to the lower right of Orion, below Rigel, the star that marks the hunter’s foot.

Estimates of Arneb’s distance vary by quite a bit — from as close as about 1300 light-years, to as far as about 2200. Astronomers compare the star’s distance to how bright it appears in our sky to determine its true brightness. At the lesser distance, the star would be more than three times fainter than at the greater distance. And that factors into the understanding of the star’s mass, its life cycle, and its fate.

Probably the best measurement of the distance comes from Gaia, a space telescope. It’s measured the distances to roughly 1.7 billion stars. Above Earth’s atmosphere, it has a sharp view of the heavens, helping it to make more precise measurements.

Gaia says that Arneb is a little more than 1900 light-years away. That means the star is roughly 10,000 times brighter than the Sun. It’s a supergiant — it’s many times the size and mass of the Sun. And it’s nearing the end of its life. In the next million years or so, it’s expected to explode as a supernova — giving Orion a real hotfoot.

Script by Damond Benningfield

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