What Is A Light Year?
While the term "light year" sounds like a measurement of time, it is actually a measurement of distance. A light year is the distance light can travel in one year.
In a vacuum like outer space, light travels at a speed of 186,282 miles per second, so the distance light can travel over an entire year is very, very far. That makes light years useful for measuring the enormous distances of outer space.
To help put light years into perspective, let me list some distances to known objects measured in light years:
The average distance between the Earth and the Sun is 93 million miles, or about 0.000016 light years, so it takes about 8 minutes and 20 seconds for light from the sun to reach Earth.
The closest star besides the sun is a star called Proxima Centauri, which is about 4.24 light years away. That means it would take 4.24 years for light from Proxima Centauri to reach Earth.
Our own galaxy is the Milky Way galaxy, and the closest neighbor galaxy is called the Andromeda galaxy, which is about 2.5 million light years from Earth. So let that sink in for a moment. The Andromeda galaxy is our closest neighbor galaxy, and it still takes 2.5 million years for its light to reach Earth!
So then, how big is the whole universe? The observable universe, which is the part of the universe we can see from here on Earth, is estimated to be about 93 billion light years across. It would take light 93 billion years to travel across the observable universe.
But if the observable universe is the part that we can see, how big is the entire universe? Nobody knows for sure, but one estimate is that the whole universe is 250 times larger than the observable universe.
This all helps to put the universe into perspective. It takes light just 8 minutes to travel from the Sun to Earth, but about 93 billion years to travel across the observable universe. #science #astronomy #space #light
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