The white glow of the Milky Way is made by billions of stars

November 24, 2012 12:48 am

When you look up at the sky on a clear night, you see thousands of tiny points of light. A couple of the brightest points might be planets in the solar system. The rest are all stars. If you look closely, you might see a thick glowing band of faint white light crossing the sky. To see it, you’ll need to be somewhere without many streetlights. Ancient Greeks named this band of light the .

The Sun is a star. It’s a lot closer to Earth than any other star, so it appears a lot brighter. The white glow of the Milky Way is made by billions of stars so far away that our eyes can’t see them as individual points of light.

WHAT IS THE MILKY WAY?

The Milky Way is a huge group of stars called a galaxy. There are billions of stars in the Milky Way. The Sun and all nearby stars are part of the Milky Way Galaxy. There are also huge clouds of gas and dust in between the stars. New stars form in the clouds of gas and dust.

The Milky Way Galaxy is shaped like a thick disk turning in outer . There is a big bulge at the center of the disk. Curved arms spiral into the central bulge. The whole thing looks like an enormous whirlpool or pinwheel. Our Sun and solar system are in one of the whirlpool’s arms out toward the edge of the disk. That’s why the Milky Way looks like a band of light in the night sky. We’re looking at the edge of the disk instead of the round face.

The Milky Way turns slowly. Everything in the Milky Way orbits (circles) the center of the galaxy. It takes about 250 million years for our solar system to go once around the center of the Milky Way.

Astronomers think there might be an enormous black hole at the center of the Milky Way. A black hole sucks in everything around it. A black hole is invisible. Not even light can escape from a black hole.

The Milky Way is not the only galaxy in the universe. With powerful telescopes, we can see billions of other galaxies. Many of them are shaped like our own Milky Way, but some look like giant balls or strands of trailing stars.

HOW BIG IS THE MILKY WAY?

The Milky Way is huge. The entire Milky Way is about 100,000 light-years across. Astronomers measure great distances in light-years. One light-year is how far light travels in one year. Light travels extremely fast. A flash of light goes almost 6 trillion miles (10 trillion kilometers) in one year. That’s a 6 with twelve zeroes after it: 6,000,000,000,000! Even at that blazing speed, it would take a flash of light 100,000 years to cross the Milky Way.

The bulge at the center of the Milky Way is about 10,000 light-years thick. Our solar system is about 25,000 light-years from the center of the galaxy.

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