The distances between objects in space are so great that everyday measurements such as miles or miles become too small to be used reasonably. Astronomers use light years as a measure of distance in space. A light year is an easy way to measure, which is the distance light travels in a year. Although it is called a light year, it is important to note that it is a measure of distance and not time. Light is the fastest known thing in the universe, with a speed of 186,000 miles per second (300,000 kilometers per second). A 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 on Earth, some of which are more than 12 billion light-years away, according to NASA.
Although light is the fastest thing in the universe, its speed is still finite. The light emitted by one object needs time to reach another. Whenever we look at space, we are actually seeing through time itself. For example, sunlight takes about eight minutes to reach Earth. So when we look at the sun, we see it as it was eight minutes ago. If you were in 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 closest star to our sun is Proxima Centauri 4.2 light-years away, so when we look at it with 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 through 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 formed. The furthest we can see physically is cosmic microwave background radiation (CMBR). The CMBR is the oldest form of light in the universe, having formed only 380,000 years after the Big Bang. This means that we can see almost 13.8 billion years in the past, seeing the universe before the first stars and galaxies formed.
If you travel far from the solar system, you could look back and see our solar system as it appeared in the past. For example, if you traveled to a planet 6,000 light-years away, you could look back and see the Earth as it was 6,000 years ago. If you had a telescope powerful enough to solve 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 the formation of our solar system.
Aidan Remple July 2, 2022 in Science