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The Center of the Universe
The first person to come up with a scientific theory about the size and shape of the Universe was a Greek astronomer named Ptolemy, who lived in the 2nd century. Ptolemy's Universe placed Earth at the center, while the other planets, the Sun, and the stars revolved around it. Most people accepted this idea, but in the 16th century, Copernicus (right), a Polish scientist, said that Earth was not in the center of the Universe. Based on his observations, he said that the Earth and the other planets revolved around the Sun. Early in the 20th century, astronomers realized that the Sun wasn't the center of the Universe. They discovered that the Sun is just one of billions of stars in the Milky Way, nowhere near the center of the galaxy. There are about 100 billion galaxies that make up the Universe, each one containing billions of stars.
Size: the observable Universe is over 10,000 megaparsecs across
Age: about 13 billion years
Significance: everything that we know of is within the Universe (along with lots of other stuff we don't know anything about)
Origin: Big Bang
Composition: around 100 billion galaxies in groups and clusters
Distances in the Universe are so vast that they're measured in light-years. In one year, light travels:
almost 600 miles
almost 600,000 miles
almost 6,000,000,000 miles
Correct!
Galaxies are so large that it takes light thousands of years to cross them.
In the early years, everything in the Universe was just gas.
Fact
As the Universe expanded and cooled, gravity formed stars and galaxies out of this gas. Gravity continues to form stars in galaxies today.
The basic forces . . . that govern our lives on Earth and that govern the workings of the Universe are one and the same . . . We live in one Universe.
Charles Liu, astrophysicist