Scientists say there as many stars in the sky as there are grains of sand on a beach because there are numerous galaxies in the universe. A galaxy is a group of stars, planets, and other objects in space. Each star spins around a center of high gravity in the same way planets may spin around the Sun in a solar system. Galaxies are huge. They can contain trillions of stars, that is a number with twelve zeroes (1,000,000,000,000).
Before the 1900s, scientists and astronomers, people who study space, used to believe that all the stars of the universe were part of one giant group. In 1917, however, Thomas Wright suggested there were many different groups of stars and later on other astronomers proved his theory. The idea of different galaxies was born.
Even though galaxies are huge and expansive, there is also a lot of empty space between the different galaxies. Believe it or not, scientists estimate that there are over 100 billion galaxies (100,000,000,000) in the universe, and if most of them contain a trillion stars, it is easy to see now why there may be more stars than grains of sand on a beach. They believe there may be clusters of galaxies separated by space as well.
Galaxies are classified based on their shapes. There are four main shapes of galaxies in the universe. A spiral galaxy appears to have long arms that spiral around the its center. The older stars are towards the center, and the newer developing stars are part of the 'arms' of the galaxy. This is where the Earth's solar system is located it its galaxy.
The second type of galaxy is called barred spiral. It is similar to the spiral but there is a long bar shape in the middle with spirals coming off the ends. The third type is the elliptical which is a large mass of stars all clumped together in the shape of an elliptical disk. It could be compared somewhat to an oval shape squeezed together on the ends.
The final type is an irregular galaxy. These types do not fit into a particular pattern or shape and are usually formed when two other types of galaxies collide with one another. The collision causes the galaxies to lose their elliptical or bar shape and instead, they become irregular. All of this movement and colliding, of course, takes place over millions or billions of years.
Astronomers know the most about the Milky Way Galaxy since it is the galaxy containing the Earth and its Solar System along with the seven other planets, and of course Pluto. The Milky Way is part of a cluster group of about 3,000 other galaxies. It is a spiral-shaped galaxy made up of more than 300 billion (300,000,000,000) stars. The Sun is one star that is located in the Milky Way galaxy. The word galaxy actually comes from a Greek word which means milky.
Andromeda is the name of the closest galaxy to the Earth and the Milky Way galaxy. It is located 2.6 million light years away from the Earth, which means it would take a beam of light about that long to reach the Andromeda. One end of most galaxies to its other end is about 100,000 light years across.
In summary, the Earth belongs to the Milky Way galaxy which is also like most galaxies, containing a lot of empty space. There are four different types of galaxies, each with their own characteristics. Finally, like many science fiction movies state, most stars are in galaxies far, far away, and it would take millions and millions of years to travel to the billions of galaxies in the universe.