Earth Science

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After discovering that there are galaxies beyond the Milky Way, Edwin Hubble went on to measure the distance to hundreds of other galaxies. His data would eventually show how the universe is changing and would even yield clues as to how the universe formed.

Redshift. If you look at a star through a prism, you will see a spectrum, or a range of colors through the rainbow.

The spectrum will have specific dark bands where elements in the star absorb light of certain wavelengths. By examining the arrangement of these dark absorption lines, astronomers can determine the composition of elements that make up a distant star.

In fact, the element helium was first discovered in our Sun not on Earth by analyzing the absorption lines in the spectrum of the Sun. While studying the spectrum of light from distant galaxies, astronomers noticed something strange.

The dark lines in the spectrum were in the patterns they expected, but they were shifted toward the red end of the spectrum, as shown in the Figure below.

This shift of absorption bands toward the red end of the spectrum is known as redshift (- the shift of spectral lines toward longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects).

Edwin Hubble combined his measurements of the distances to galaxies with other astronomers’ measurements of redshift. From this data, he noticed a relationship, which is now called Hubble’s Law: the farther away a galaxy is, the faster it is moving away from us. What could this mean about the universe? It means that the universe is expanding.

The Figure below shows a simplified diagram of the expansion of the universe. One way to picture this is to imagine a balloon covered with tiny dots to represent the galaxies.

When you inflate the balloon, the dots slowly move away from each other because the rubber stretches in the space between them.

If you were standing on one of the dots, you would see the other dots moving away from you.

Also the dots farther away from you on the balloon would move away faster than dots nearby.

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