A long time ago, in a Galaxy far, far away...
Have you every looked up at the sky at night and seen the stars? Have you ever wondered just what might be out there, beyond where your eyes can see? Beyond where our space ships can take us, beyond where our telescopes and satellites can see?
Astronomers have been looking for answers to those types of questions for centuries, and while we may not have answers to all of them, we know a lot more now than we did 100 or even 10 years ago. Our biggest and best telescopes and the people that operate them are constantly finding new and interesting celestial objects to study. For now though, let's focus on the big ideas.
Astronomers have been looking for answers to those types of questions for centuries, and while we may not have answers to all of them, we know a lot more now than we did 100 or even 10 years ago. Our biggest and best telescopes and the people that operate them are constantly finding new and interesting celestial objects to study. For now though, let's focus on the big ideas.
What's in a Universe?
To answer the above question simply, everything. All matter, energy and time exists in our universe. The universe contains billions and billions of clusters of galaxies. Inside each galaxy, there are billions and billions of stars. Some of those stars have planets, making solar systems much like ours. Also contained within solar systems are comets, meteor, moons, asteroids and other celestial objects. That's a lot of stuff!
As best that astronomers and scientists can tell, the Universe began almost 14 billion years ago. They theorize that the Universe began as a single, very dense point where all matter and energy was contained. This point was so dense that it became unstable and eventually "exploded" outwards, throwing material to the far reaches of what is now the Universe. Scientists named this idea the Big Bang Theory (no, not the hit TV series). As proof of their theory, scientists can prove that the universe is expanding even now. They claim that the universe wouldn't just have started expanding on its own, it had to start somewhere a long time ago. Even now, galaxies are moving away from each other, but all around a central point.
As best that astronomers and scientists can tell, the Universe began almost 14 billion years ago. They theorize that the Universe began as a single, very dense point where all matter and energy was contained. This point was so dense that it became unstable and eventually "exploded" outwards, throwing material to the far reaches of what is now the Universe. Scientists named this idea the Big Bang Theory (no, not the hit TV series). As proof of their theory, scientists can prove that the universe is expanding even now. They claim that the universe wouldn't just have started expanding on its own, it had to start somewhere a long time ago. Even now, galaxies are moving away from each other, but all around a central point.
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Think of each galaxy like a dot on a balloon. As you inflate the balloon, the galaxies are moving farther and farther apart as the space between them gets inflated. This is similar to what is happening throughout the universe.
Galaxies Galore
There are billions and billions of galaxies throughout the Universe and they come in many different shapes and sizes. A long time ago, scientists decided that, like everything else in science, galaxies needed to be classified so we could tell one galaxy from another. A galaxy is basically a big collection of stars, dust and gas that usually surrounds a black hole. The gravity of the black hole at the center is what holds the galaxy together and helps keep it in place. (Most of these black holes are not active though, otherwise they might eventually suck the contents of their galaxy in and destroy it.)
Galaxies are most often sorted by shape. There are three main categories for galaxies: Elliptical, Spiral, and Irregular.
Galaxies are most often sorted by shape. There are three main categories for galaxies: Elliptical, Spiral, and Irregular.
Spiral galaxies have a center bulge, almost like a globe. The stars inside this globe like structure are packed in very tightly so the center of a spiral galaxy tends to be much brighter than the outer sections. These outer sections are called arms, and they curve in wide arcs around the outer edge of the spiral galaxy as it spins. Our galaxy, the Milky Way, is a spiral galaxy and our solar system sits on the edge of one the galaxy's long arms.
Elliptical galaxies are dense clusters of stars shaped roughly into an sphere or sometimes an oval. We usually see an oval like shape from Earth. These galaxies are most dense at the center and therefore brightest at the center. The brightness decreases as you move farther from the center because stars are not as closely packed.
Irregular galaxies are just that: irregular. They don't have a definite shape or structure but are largely filled with dust, meaning that individual stars are hard to see clearly.
Elliptical galaxies are dense clusters of stars shaped roughly into an sphere or sometimes an oval. We usually see an oval like shape from Earth. These galaxies are most dense at the center and therefore brightest at the center. The brightness decreases as you move farther from the center because stars are not as closely packed.
Irregular galaxies are just that: irregular. They don't have a definite shape or structure but are largely filled with dust, meaning that individual stars are hard to see clearly.