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A light year is the distance light travels in a year through a vacuum. Astronomers use it to describe large distances. Our solar system would have to be 800 times larger to have a diameter of one light-year. The closest star is Proxima Centauri at 4.2 light-years away. By knowing how fast light travels, we can appreciate the vast distances of the universe.
A light year is the distance that light travels in one year through a vacuum or empty space. Light moves through a vacuum at just over 186,282 miles (299,792 km) per second, making a staggering 5.8 trillion miles (9.4 trillion km) in a year. With distances this large, relative terms like “miles” and “kilometers” become inefficient and meaningless. Instead, astronomers speak in terms of light years to describe large distances.
Before we can appreciate talking about distances in terms of light years, it helps to understand how far a single extends. As for our solar system, defined for this exercise by the orbit of the former planet Pluto, the solar system would have to be 800 times larger to have a diameter of one light-year. In other words, the sun is about 93 million miles from earth, and there would have to be 31,620 round trips from earth to the sun to travel the distance of one light year.
In addition to the light year, scientists also speak in terms of light seconds and light minutes. An astronomical unit (AU) – the distance from the earth to the sun – is 8.3 light minutes. In other words, it takes 8.3 minutes for sunlight to reach the earth. Conversely, the sun is 8.3 light-minutes from the earth.
There is no star that is exactly one light-year away from our solar system. The closest star is Proxima Centauri at 4.2 light-years away. Next is the double star Alpha Centauri A and Alpha Centauri B, 4.3 light-years away.
By knowing how fast light travels, one can begin to appreciate the vast distances of the universe when speaking in terms of light years. For example, the light emitted by Alpha Centauri today will take 4.2 years to reach Earth, so when we look at that star, we see it as it was 4.2 years ago. In essence, we look back in time when we look into space.
