35 Outside the Solar System-High

Outside the Solar System Written by Patricia Walsh and Ron Fridell

Introducing Deep Space On a dark, clear night away from city lights, look up. Look way up. Do you see points of light dotting the black canopy of sky overhead? Most of the points of light you see are stars. Some of the points of light you see are double stars that orbit each other. And some of the points of light are really massive collections of stars called galaxies. What you can see, and even what you cannot see, is all part of deep space. Deep space is the area of space that is beyond our own Solar System. It is space beyond our star— the Sun— and the planets, asteroids, and comets that orbit our Sun.

Exploring Space For thousands of years, people looked up and used the stars to navigate their way across Earth's land and seas. Then, about 500 years ago, people developed the first telescopes to get a closer look at the objects in the heavens overhead. People immediately began improving the telescopes. They made them bigger and more powerful. The images of the stars they could see got clearer and brighter. Today, huge telescopes sit on top of mountains and even orbit in space above Earth. Scientists also developed another kind of telescope. The radio telescope, which detects radio waves given off by objects in space, allows us to detect things that cannot be seen with optical telescopes.

In 1961, the Soviet Union put the first man into space. Now people have even landed on the Moon. But no one has ever traveled into deep space. So how do we know what exists way, way out in space? How do we know what makes up the universe? The answer lies in the information we gather from telescopes and spacecraft. Like so many space explorers before you, plant your feet firmly on Earth. Then sharpen your science skills and pack your imagination. You are about to journey among the 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 are already familiar with your own space neighborhood— Planet Earth, our Moon, the other planets, and our Sun. These are all in our Solar System. But it is only a very tiny part of a gigantic, bustling universe filled with vast space and billions and billions of other objects. It's time to leave Earth and head toward the outer edge of our Solar System. 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'll feel a bump as you leave the Solar System. The bump is caused by the solar wind at the boundary between our Solar System and deep space. You knew the bump was coming because Voyager 2, an unmanned spacecraft launched in 1977, gave us advance warning. You're traveling much faster than Voyager 2, so you'll be overtaking 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've reached our nearest neighboring star, dim and cool Proxima Centauri. Proxima Centauri and Alpha Centauri are part of a multiple-star system. Alpha Centauri's two stars are 4.3 light-years away and are almost identical to our Sun. Standing on Earth, you saw constellations made of stars arranged in interesting patterns— a lion, a swan, a centaur. But as you travel among the stars, you'll notice that these constellations are not dots on a flat surface— they're actually stars that are very far from each other. Math Moment The distance between stars is so great that scientists use a measurement called a light-year to measure it. One light-year is the distance that light travels in one Earth 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?