Heart of the Galaxy

StarDate: July 5, 2009

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The Moon passes across the heart of the Milky Way galaxy tonight. The Moon lines up above the "spout" of the teapot-shaped constellation Sagittarius. The core of the Milky Way is in that same direction -- 27,000 light-years away.

The Moon is so bright that it overpowers the light of the stars and other objects around it. Even when the Moon isn't in the sky, though, we can't see the core of the Milky Way because it's hidden behind a veil of dust -- vast clouds of it that lie between the core and Earth. Just as clouds blot out the Sun, the clouds of dust absorb the light from the stars behind them.

So studying the core is a bit tricky.

Some visible light does get through -- the light of the most powerful stars. Other forms of energy shine right through the clouds, but they're blocked by Earth's atmosphere. To see them, astronomers must lift their telescopes above the atmosphere.

These telescopes reveal massive star clusters and the remnants of exploded stars. They show clouds of gas that are sculpted by intricate magnetic fields. And they show evidence of a black hole that's several million times as massive as the Sun. Bright, heavy stars whip around the black hole in a hurry, accelerated by its powerful gravity.

So the center of the galaxy is a bright, crowded, busy place -- but one that's tough to see and study. But we can at least see where it is -- tonight, beyond the bright glare of the gibbous Moon.

Script by Damond Benningfield, Copyright 2009

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