Moon and Spica

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Moon and Spica

The full Moon has a follower tonight: Spica, the leading light of Virgo. It’s below the Moon as it climbs into good view by 9 or 10 p.m., and closer to the lower left of the Moon at first light tomorrow.

Spica is an amazing system. It consists of two stars, not one. But they’re only a few million miles apart — much, much closer than Earth is to the Sun. In fact, they’re so close together that not even the biggest telescopes can see them as individual stars — they form a single pinpoint of light.

At such a tight separation, the gravity of each star distorts the shape of the other. So instead of balls, both stars are shaped like eggs, with the skinny end of each one pointed toward its companion.

The stars bombard each other with radiation and with winds of charged particles. Where the winds ram into each other, they create X-rays. All of that makes the companion-facing side of each star a good bit hotter and brighter than the rest of the star.

Things will get even brighter before too long. The bigger star is at the end of its normal lifetime. It’s so massive that it’s puffing up to become a supergiant. And at the end of that phase of life, it’s likely to explode as a supernova. It will leave behind a small, ultra-dense core: a neutron star. And the blast should send the smaller companion star careening through the galaxy — the runaway survivor of an amazing star system.

Tomorrow: obsolete constellations.

Script by Damond Benningfield

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