34 Outside the Solar System-Mid

Outside the Solar System Written by Patricia Walsh and Ron Fridell

Introducing Deep Space Look up on a dark, clear night away from city lights. Do you see the points of light overhead? Most of the points of light you see are stars. Some points of light are really double stars that orbit, or go around, each other. Some points of light are groups of stars called galaxies. What you see and what you cannot see is all part of deep space. Deep space is everything beyond our Solar System. It is space that is beyond our star— the Sun— and the planets, asteroids, and comets that orbit the Sun.

Exploring Space For thousands of years, people used the stars to navigate their way across Earth's land and seas. About 500 years ago, people developed the first telescopes. Telescopes let them get a closer look at the objects in the night sky. Over time, telescopes have been improved in many ways. Today, huge telescopes sit on top of mountains. Space telescopes orbit Earth. Scientists also use another kind of telescope. The radio telescope detects radio waves given off by objects in space, which allows us to detect things that cannot be seen with optical telescopes.

Humans have gone into space. We have even landed on the Moon. But no one from Earth has ever traveled farther than our Moon. No one has traveled outside our Solar System into deep space. Pack your imagination. You're about to journey among the billions and billions of stars, planets, and galaxies in the universe. Word Wise The word telescope comes from the Greek word teleskopos. The word part tele- means "far" and -skopos means "seeing." Our modern-day telescopes let us see far into space.

Out of This World You already know your space neighbors— the Moon, the other planets, and our Sun. These are in our Solar System. But it is only a very tiny part of a gigantic universe. Outside the Solar System is vast space and billions and billions of other objects. It's time to leave Earth, and head toward deep space. Take a moment to look back over your shoulder as you zip past the outer planets of Uranus and Neptune. Earth looked like a blue dot for a while, but now it has disappeared. You are leaving our Solar System. Did you feel a bump? It was caused by solar wind where the Solar System ends and deep space begins. The bump should not have surprised you. Voyager 2, an unmanned spacecraft launched in 1977, let scientists know about the bumpy solar winds. You're traveling much faster than Voyager 2, so you might pass it as you cross into interstellar space.

Among the Stars You've traveled a very long distance now. You have come 4.2 light-years from Earth. You're arriving at Earth's nearest star neighbor. It's the dim and cool Proxima Centauri. Next you'll see Alpha Centauri. It is much brighter than dim Proxima. Up close, you can see that Alpha Centauri has two stars that are very much like our Sun. Standing on Earth, you saw constellations made of stars arranged in interesting shapes, like a lion and a centaur. But now you'll notice that these constellations aren't groups of dots on a flat surface. They're actually stars that are very far from one another. Math Moment The distance between stars is vast. Scientists use a measurement called a light-year to measure it. A light-year is the distance that light travels in one year. One light-year is about 9.5 trillion kilometers (5.9 trillion mi.). About how many kilometers (or mi.) from Earth is our closest star neighbor?