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Real-Life Math

According to the Big Bang theory, the universe exploded from 1 point billions of years ago. The universe has continued to expand ever since.

Edwin Hubble was the first person to discover that the universe was expanding. This expansion means that galaxies outside our galaxy are moving rapidly away from us. The more distant a galaxy is from us, the faster it is moving away.

Astronomers use a theory called Hubble's law to figure out how fast an object in space is moving away from us.

The law is written like this: v = H x d
v = the velocity
H = Hubble's constant -- Hubble figured out that this number is always 75 kilometers per second (kps) per megaparsec. A megaparsec is 1,000,000 parsecs. A parsec is about 3 light-years. Light travels 5.8 trillion miles per year.
d = the distance (how far a galaxy is away from us)

Here's an example of how the equation works:

d = a galaxy is 1 megaparsec away from us
H = 75 kps per megaparsec
d (1) x H (75) = v (75)
This galaxy is moving away from us at a speed of 75 kps

1. Now have a look at the galaxy you've been studying. Galaxy A is moving at a speed of 500 kps away from us. How far away is it? Remember that distance is measured in megaparsecs.

2. Is galaxy A moving faster or slower than galaxy B, which is 10 megaparsecs away?

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