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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 Milky Way.
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 space. 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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