# what is light year and how it works?

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A light year is a way of measuring distance.

When astronomers use their telescopes to look at stars, things are different. The distances are gigantic. For example, the closest star to Earth (besides our sun) is something like 24,000,000,000,000 miles (38,000,000,000,000 kilometers) away. That's the closest star. There are stars that are billions of times farther away than that. When you start talking about those kinds of distances, a mile or kilometer just isn't a practical unit to use because the numbers get too big. No one wants to write or talk about numbers that have 20 digits in them!

­So to measure really long distances, people use a unit called a light year. Light travels at 186,000 miles per second (300,000 kilometers per second). Therefore, a light second is 186,000 miles (300,000 kilometers). A light year is the distance that light can travel in a year, or:

186,000 miles/second * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365 days/year = 5,865,696,000,000 miles/year

A light year is 5,865,696,000,000 miles (9,460,800,000,000 kilometers). That's a long way!

Using a light year as a distance measurement has another advantage -- it helps you determine age. Let's say that a star is 1 million light years away. The light from that star has traveled at the speed of light to reach us. Therefore, it has taken the star's light 1 million years to get here, and the light we are seeing was created 1 million years ago. So the star we are seeing is really how the star looked a million years ago, not how it looks today. In the same way, our sun is 8 or so light minutes away. If the sun were to suddenly explode right now, we wouldn't know about it for eight minutes because that is how long it would take for the light of the explosion to get here.

• Light year is the distance that light travels in one year

• "Works"? A Light Year doesn't "work". A Light Year is merely the distance that light (in a vacuum) travels in the time period of one year.

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• Anonymous
7 years ago

Light year is the distance that light travels in one year. It doesn't work anything.

• Light year is a unit to measure distance...n not years...

1 light year is the distance travelled by light in 1 year (speed of light is 300000 km/s) so its a really huge distance. Light year is normally used to measure the distance between to planets or stars or galaxies...

Source(s): I am an Engineer and studied this in physics.
• A "light-year" is a unit of distance.

It represents the distance that light can travel, in the vacuum of space, in one Earth-year.

We normally use the speed of light in a vacuum

299 792 458 m/s

and multiply it by the "average Gregorian year" in seconds:

365.2425 days of 86,400 seconds each

= 31 556 952 seconds

Thus, one light-year is a distance of

9.46*10^15 metres (approximately)

When we say that a galaxy is 2 million light-years away, we mean (in astronomy) that it took the light 2 million years to travel (at the speed of light, of course) from the galaxy to us.