Download Getting to Know: Structure of the Universe

Getting to Know: Structure of the Universe
Humans have always been curious about what lies beyond our planet. In ancient times, people studied the skies and found images that helped them tell their stories. In more modern times, we imagine traveling to far-off galaxies and perhaps discovering other forms of life. However, it is not likely that this will happen anytime soon because of the huge distances required to reach the other bodies that share our universe. A galaxy is a collection of stars, gases, dust, planets, and other astronomical bodies. There are billions of galaxies in the universe, each of which contains billions of stars. If you look at a distant galaxy, the stars appear The Sombrero galaxy is approximately
very close together, but this appearance is 28
million light years away. This galaxy may
deceiving. In fact, the stars in a galaxy are have
a black hole at its center. (Image from
extremely far apart. Our own galaxy, the NASA.)
Milky Way galaxy, is a good example. The next nearest star to Earth, besides the Sun, is Proxima Centauri. Light travels 9,460,000,000,000 km in one year or 300,000 km per second. Even if you traveled at the speed of light, it would still take you 4.3 years to reach Proxima Centauri.
Another galaxy, the Sombrero galaxy, which got its name because it looks like a traditional
Mexican sombrero, is at least 28 million light years away. Even if spaceships could travel at the
speed of light, it would still take 28 million years to reach the Sombrero galaxy.
How big are galaxies?
Galaxies are huge. Our own Milky Way galaxy is just 100,000 light years across and contains some 200 billion stars. The Sombrero galaxy is 50 million light years across, and it has approximately 10 times the number of stars contained in our galaxy. Several galaxies can be seen from Earth, but they tend to look like stars in the night sky.
The billions of stars in each galaxy are so far away that their light shines as one. One example
is the Andromeda galaxy. It is one of the Milky Way’s closest neighbors at 2.5 million light years
away. This means that the light you see when you look at Andromeda left the galaxy 2.5 million
years ago. When you look at this galaxy, you are
peering into the past. You are seeing what the
galaxy looked like 2.5 million years ago.
Do all galaxies look the same?
Galaxies have a variety of shapes. Most scientists classify galaxies as elliptical, spiral, or irregular. Elliptical galaxies have a circular or oval shape. Spiral galaxies have two or more spiraled arms of stars coming from the central region. Barred spiral galaxies are similar to spiral galaxies but with an elongated middle. Some galaxies do not fit into any classification scheme and are called irregular galaxies.
Concept: Structure of the Universe
Getting to Know
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Galaxies are classified by their shape.
(Image from NASA.)
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Misconception 1: I saw a picture of the Milky Way galaxy on the Internet. Is the
picture a real image of the Milky Way galaxy?
The Milky Way galaxy is very big, and no cameras have yet been able to travel outside
of the Milky Way to take its picture. Several galaxies look similar to the Milky Way, so
pictures of those galaxies are sometimes used online as representative images.
How is a solar system different from a galaxy?
A solar system is a star and the objects that
orbit that star. Scientists have found several
solar systems in our galaxy, many of which have
planets surrounding them. If the Milky Way
galaxy were the size of a quarter, the Sun would
be the size of a single speck of dust on that
quarter. The Sun and our solar system are just
one tiny part of the entire Milky Way galaxy.
If the Milky Way were the size of a quarter,
our Sun would be the size of a speck of dust.
Remember that the universe contains billions
of galaxies, more than any person can count.
In this lesson, you will learn more about what
scientists have found out about the universe so
far—and what questions they still have.
Misconception 2: Can two galaxies bump into each other in space?
Galaxies do sometimes collide in space. Galaxies are constantly moving and spinning,
and they are not evenly distributed in space. When a collision does take place, it takes
hundreds of millions of years for the two galaxies to completely merge, and it can cause
a galaxy with a new shape to result.
Concept: Structure of the Universe
Getting to Know
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.