SPACE — Contrary to its name, a light year is a measure of distance, not time. A light year is the distance traveled by a beam of light in one Earth year, equivalent to approximately 6 trillion miles or 9.7 trillion kilometers.
On the scale of the universe, measuring distances in miles or kilometers is impractical given the enormous numbers. It’s much easier for astronomers to measure a star’s distance from us in the time it takes for light to travel that distance. For example, the closest star to our sun, Proxima Centauri, is 4.2 light years away, meaning the light we see from it takes more than four years to reach us.
How Far Is One Light Year?
The speed of light is constant throughout the universe and is known with high precision. In a vacuum, light travels at 670,616,629 mph (1,079,252,849 km/h). To find the distance in a light year, multiply that speed by the number of hours in a year (8,766). The result: One light year is 5,878,625,370,000 miles (9.5 trillion km).
Scroll to read
Scroll to read
At first glance, that might seem like an enormous distance, but on the cosmic immense scale, that length is negligible. One estimate places the diameter of the known universe at 28 billion light years.
Why Use Light Years?
Measuring in miles or kilometers on an astronomical scale is impractical given the numerical scale used. Starting from our cosmic neighborhood, the closest star-forming region to us, the Orion Nebula, is 7,861 miles away.000.000.000.000 miles away and expressed in light years is 1,300 light years. The center of our Milky Way galaxy is about 27,000 light years away.
The closest spiral galaxy to us, the Andromeda galaxy, is 2.5 million light years away. Some of the most distant galaxies we can see are billions of light years from us. The galaxy GN-z11 is considered to be the most distant galaxy that can be detected from Earth, which is at a distance of 13.4 billion light years. Imagine if it was written in miles or kilometers.
Like degrees, light years can also be broken down into smaller units of light hours, light minutes, or light seconds. For example, the sun is more than 8 light minutes away from Earth, while the moon is only one light second away. Scientists use this term when talking about communication with satellites or space explorers. Due to the limited speed of light, it would take more than 20 minutes to send a signal to the Curiosity rover on Mars.
Measuring in light years also allows astronomers to determine how far in time they are looking. Because light takes time to reach our eyes, everything we see in the night sky has already happened. In other words, when you observe something 1 light year away, you see it as it appeared exactly one year ago. We see the Andromeda galaxy as it appeared 2.5 million years ago. The most distant object we can see, the cosmic microwave background, is also our oldest view of the universe, occurring just after the Big Bang about 13.8 billion years ago.
Alternatives to Light Years
Astronomers also use parsecs as an alternative to light years. Short for parallax-second, parsec comes from the use of triangulation to determine the distance to stars. To be more specific, this is the distance to a star whose position appears to shift by 1 arcsecond (1/3,600 degree) in the sky after Earth has orbited halfway around the sun. One second of arc is equal to 3.26 light years.
Whether it’s light years or parsecs, astronomers will continue to use both to measure distances in our vast and immense universe. However, if you have another input for describing the distances of objects in the universe, it’s fine to suggest it to astronomers. Source: Space.com
“).attr(
type: ‘text/javascript’,
src: ‘
).prependTo(“head”);
if ($(“.instagram-media”).length > 0)
$(”
