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 Solar System

Outer Space

Have you ever wondered what is really in outer space? What exactly is the universe? The word universe is used to refer to all of outer space. Astronomers have studied space for many years, but still have more questions than answers.

No one knows just how large our universe really is. We do know that the universe is immense and the distances between objects are tremendous. But how far is “far away”? Let's give a try. Imagine that the distance between the Sun and the Earth is equal to the size of one grain of sand. Using this size as a comparison, then the planet we call Pluto would be 30 feet away. The closest star beyond the Sun, called Alpha Centauri, would be 50 miles away. This makes it easier to understand just how far away things in outer space really are.

However, astronomers prefer to use term “light-years” to measure distances from Earth. A light-year describes how far light can travel in one year. Astronomers chose light as a reference point because it travels faster than anything else does. In fact, if you shined a beam of light all the way around the world, it could go around 7 ½ times in one second. Now that is speedy traveling! Scientists guess that the universe is at least 10 billion light-years across, and it seems to be getting larger.

The universe is made up of a lot of empty space. Huge swirling masses of stars, called galaxies, are scattered through the universe. Each galaxy is made of billions of stars. Our solar system can be found within a galaxy, called the Milky Way. The Milky Way has a shape similar to a fried egg with a nice big yellow in the center.   It is a spiral galaxy.  There are two other types of galaxies.   One is an elliptical galaxy, which is round and the other is an irregular galaxy which doesn't have any real shape.  Our solar system would be located about half-way between the yoke and the edge of the egg white.

There are many different kinds of stars, some old and some new. Some stars are brighter than others. Stars that are hottest appear white through a telescope. Stars that are not quite as hot appear yellow, like our Sun. Those stars that are even cooler will appear red in color. Stars are born, grow older, and then die. They are constantly repeating this life cycle, even though they are not really alive. Have you ever looked for the Big Dipper or the Little Dipper in the sky at night. If you have, then you have looked for constellation. Constellations are patterns of stars that form a specific shape in the sky.

In between the stars, there are cloud-like shapes of gases and dust called nebulae. A single nebula can have almost any shape. Some nebulae do not give off any light. We can see some of them because they reflect light of nearby stars. A star is born when the gases in these clouds condense enough for nuclear reactions to begin. A star is like a nuclear bomb inside a very strong box. Instead of exploding all at once, imagine the box opening and closing, releasing the bomb's energy a little bit at a time, over a long period of time. That is what a star does. A star will continue to burn up its gases and give off heat and light for millions of years. It may end its life quietly by becoming a black dwarf (a very small star that emits no visible light) when it can no longer shine. Or, it may end in a supernova explosion (a very big, bright explosion).

In addition to planets and moons in our solar system, there are bodies known as comets, asteroids, and meteors. Comets are like dirty snowballs made of frozen gases, dust, and rock particles. They travel in oblong orbits around the Sun. As they get closer to the Sun they become warmer and begin to melt. Sometimes a gas “tail” is formed from the melted gases. If you looked at a comet through a telescope, it would look like a fuzzy head with a long tail. You may have heard of Halley's Comet. This comet was named after Edmund Halley, who predicted it would return. Maybe some day you could have a comet named after you.

Asteroids and meteors are also found in space. These are really just pieces of space “junk”. They are made of bits of rock and metal. Asteroids are quite large and meteors are smaller. A meteor that enters the Earth's atmosphere at a high speed usually burns up. This kind of meteor is called a shooting star even though it is not really a star. It is called a meteorite if it lands on the ground.

Now you know the universe is enormous. It includes billions of galaxies, planets, moons, stars, meteors, comets, and so much more that is yet to be discovered. Astronomers will understand more about how stars are formed and how huge our universe really is one day. For now, we can all observe some of the amazing characteristics of outer space each night and leave the rest up to our imaginations and the scientists!