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Moon and Antares

July 18, 2013

Giant clouds of gas and dust in the depths of space make for pretty pictures in astronomy books. But the nearest cloud is close to home. In fact, we’re right in the middle of it — it surrounds our solar system.

The Local Cloud is no match for the giant interstellar clouds like the Orion Nebula, though. Its gas is so thinly spread that it reveals its presence only by absorbing traces of light from nearby stars.

Astronomers can deduce the cloud’s origin by measuring its motion through space. It’s moving away from the vicinity of the bright orange star Antares, which stands close below the Moon tonight.

Antares, which is the brightest star of Scorpius, is one of many big, heavy stars in that part of the galaxy. These stars will end their lives in titanic explosions known as supernovae. Astronomers suspect that a massive star like Antares exploded a few million years ago and hurled debris toward the solar system — the gas and dust that make up the Local Cloud.

We may find out more about the Local Cloud when the Voyager 1 spacecraft exits the Sun’s magnetic domain and plunges into the space beyond. Without the Sun’s interference, Voyager will be able to probe the Local Cloud directly.

Although you can’t see the Local Cloud, you can see where it came from. Just look southward shortly after sunset for beautiful Scorpius, which curls below the Moon. It’s ground zero for a supernova explosion that hurled an interstellar cloud our way.


Script by Ken Croswell, Copyright 2013

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