Download Arrangement of the Universe

We still have much to learn about the universe. Within the last few
hundred years, however, new tools and scientific theories have greatly
increased our knowledge. In this chapter you will learn about the
arrangement of planets and stars. You will also learn about the ways
in which astronomers explore and study space.
Arrangement of the Universe
If you look up at the sky on a clear night, you will see only a tiny
fraction of the planets and stars that exist. The number of objects in
the universe and the distances between them are greater than most
people can imagine. Yet these objects are not spread around randomly.
Gravity causes objects in space to be grouped together in different ways.
The images on page 587 show some basic structures in the universe. Like a camera lens zooming out, the images provide views of
space at different levels of size.
Our planet’s diameter is about 13,000 kilometers (8000 mi).
This is almost four times the diameter of the Moon, which orbits
Earth. An orbit is the path of an object in space as it moves
around another object because of gravity.
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Earth
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Solar System
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Our solar system and the stars you can see with
your bare eyes are part of a galaxy called the Milky Way. A galaxy
is a group of millions or billions of stars held together by their own
gravity. If the solar system were the size of a penny, the Milky Way
would stretch from Chicago to Dallas. Most stars in the Milky Way
are so far away that our galaxy appears to us as a hazy band of light.
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The universe is everything—space and all the matter and energy in it. The Milky Way is just one of many billions of
galaxies in the universe. These galaxies extend in all directions.
The word orbit can be
a noun or a verb.
Earth and other planets orbit the Sun. The Sun,
the planets, and various smaller bodies make up the solar system.
The Sun is about 100 times greater in diameter than Earth. You
could fit more than 4000 bodies the size of the Sun between
the Sun and the solar system’s outermost planet at its average
distance from the Sun. The Sun is one of countless stars in
space. Astronomers have detected planets orbiting some of these
other stars.
The Milky Way
The Universe
Astronomers study space at each of these different levels. Some
focus on planets in the solar system. Other astronomers study distant
galaxies. To learn how the universe formed, astronomers even study
the smallest particles that make up all matter.
What is the relationship between the solar system and the
Milky Way?
586 Unit 5: Space Science