Few of the wonders of the universe inspire as much awe as a grand spiral galaxy. And one of the grandest of them all sails high overhead tonight, near the handle of the Big Dipper. It's visible through small telescopes.
The galaxy is M101. It takes its name from a catalog of celestial objects compiled in the eighteenth century by French comet hunter Charles Messier. As galaxies go, M101 is fairly near by, at a distance of just 24 million light-years.
M101 looks like a glowing celestial pinwheel. Its brightest stars, which shine blue and red, form delicate spiral arms. Clouds of hydrogen gas punctuate the arms, glowing pink from the energy of the hot young stars they gave birth to.
By good luck, we see this beautiful spiral galaxy nearly face-on, so we have a perfect bird's-eye view. In fact, we know what M101 looks like better than we do our own galaxy, the Milky Way. That's because we're inside the Milky Way's disk, so we can't see its entire expanse. It's like trying to map an entire forest when you're in the middle of it and can see only the trees around you.
In contrast, any astronomers in M101 view our galaxy almost face-on, so they know exactly what the Milky Way looks like. But they probably can't judge just how spectacular their own galaxy is.
Perhaps we can arrange a trade with them: They send us a nice picture of the Milky Way, and we'll send them a picture of their galaxy -- the incredible spiral known as M101.
Script by Ken Croswell, Copyright 2008
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