|We call the science of outer space, planets, and starts astronomy. That word comes from the Greek word astron, which means star.
On a clear night look up in the sky. What can you see? The moon shining? The stars twinkling? When a person on the earth looks into the vastness of the space, the space seems to go on forever. For every star that can be seen there are billions that cannot be seen. On and on the universe goes, stretching out in all directions, farther and bigger than anyone can imagine.
The stars in the universe are grouped into huge galaxies. Some galaxies are spiral shaped, like pinwheels. Others look like big oozing blobs of light.
Our sun is only a single star among billions of stars that make up the galaxy we live in, which is called the Milky Way. On a dark night, one can sometimes see a fuzzy, milky white stripe running across the sky. That white stripe is made up of the billions of stars in the Milky Way.
Beyond the Milky Way there are billions more stars in our neighboring galaxy called Andromeda Galaxy. Even though Andromeda is closer to us than most other galaxies, it is almost two million light years away. That means the light traveling from Andromeda to earth takes nearly 2 million years to arrive.
Beyond Andromeda, there are still billions more galaxies. All these billions of galaxies seem to be flying out away from each other. The universe is growing bigger.
When astronomers observed how galaxies seem to be flying away from each other, they came up with a theory based on the evidence for how the universe began. Their idea is called the Big Bang theory. Many scientists think that about 15 billion years ago all the matter in the universe was packed into a super dense ball. No one knows exactly what it was or why it happened, but something caused this ball to explode with a big bang. The explosion set chunks of matter flying into space. Eventually, this matter became stars, planets, and everything else in our universe.
Astronomers learn about distant planets, stars and galaxies by looking through powerful telescopes, made of lenses and mirrors that let the human eye focus on objects far, far away.
Today’s astronomers use another kind of telescope called a radio telescope. Radio telescopes use sound, not sight, to learn about the universe. They collect faint signals from outer space. They gather information that might not be seen through telescope lenses.
Directions: Answer the following questions.