The distances between objects in space are so great that everyday measurements like kilometers or miles become too small to be of reasonable use. Astronomers use light years as a measure of distance in space. A light year is a simple form of measurement representing the distance light travels in one year. Although it is called a light year, it is important to note that it is a measure of distance, not time. Light is the fastest known thing in the universe, traveling at 186,000 miles per second (300,000 kilometers per second). One light year is equivalent to 5.88 trillion miles (9.46 trillion kilometers).
Distance and time
Hubble’s Deep Field contains some of the most distant galaxies from Earth, some more than 12 billion light-years away, NASA
Although light is the fastest thing in the universe, its speed is still finite. It takes time for light emitted from one object to reach another. Whenever we look into space, we are actually seeing through time itself. For example, light from the sun takes about eight minutes to reach Earth. Thus, when we look at the sun, we see it as it was eight minutes ago. If you were on Neptune, you would see the sun as it was four hours ago. For objects that are even further away from us, we can see even further back in time. The nearest star to our sun is Proxima Centauri, 4.2 light years away, so when we look at it through a telescope, we see it as it was 4.2 years ago. This simple but profound fact about our universe means that we can see the evolution of space over time. The most distant known galaxies are more than 12 billion light-years away, and so we can see the universe as it was 12 billion years ago. We can see objects that emitted their light many billions of years before our solar system even formed. The farthest we can physically see is the cosmic microwave background radiation (CMBR). The CMBR is the oldest form of light in the universe, formed only 380,000 years after the Big Bang. This means we can see nearly 13.8 billion years into the past, seeing the universe before the first stars and galaxies even formed.
If you travel far from the solar system, you could look back and see our solar system as it looked in the past. For example, if you travel to a planet 6,000 light years away, you can look back and see Earth as it was 6,000 years ago. If you had a powerful enough telescope that could make out the earth’s surface, you could witness the birth of civilization. Or if you traveled to a galaxy 4.5 billion light years away, you could look back and see how our solar system formed.
Aidan Remple July 2, 2022 in Science
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