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Light Year
Well. Let me start by asking you some questions. Don’t worry, I will help you answer !

How far is the nearest railway station from your home?
          Your answer may be 5 miles.
How far is the nearest airport from your home?
          You may answer, 25 miles.

Now I will takeover and answer.
The distance from Florida to Washington state is 3200 miles.
The distance from New York to cape town is ~ 7800 miles.   
        
If I ask you to say or write the 7800 miles in words, you would write “seven thousand and eight hundred” miles or “seventy eight hundred” miles. That looks easy !

Now, Let’s go into larger scale !!
Earth to sun distance - 92,955,807.273 miles  
Sun to the nearest star: 24690226567370 miles

Can you say the last one in words? Getting dizzy?? It is not only difficult to say that but also difficult to use in calculations.

Now, Lets come to the point.

The units we often use like meter, kilometer, miles, knots etc. to measure distance are only suitable for small values. They are easy to use and execute in calculations at smaller levels. Ever since humans started to explore the cosmos, these units did not work for them since the numbers were huge. It was very difficult to use these huge numbers in calculations or to document that.

They decided to solve this problem and found a solution, a Light Year !

Just how 1 kilometer is easy to say and use in calculations than 1000 meter, they wanted to shrink the lager scale.

Light year by definition: It is the distance that light covers in one year when it travels.

The speed of light is approx. 186,282 miles per second. So it is 670615200 mile per hour and 16094764800 miles per day and at last 5874589152000 miles per year.
The official value is, 1 light-year = 9460730472580800 meters.
So just how, 1 km is 1000 meters, 1 light year is 9460730472580800 meters.
In simple words, if you switch on a powerful torch into space, it would have traveled 9460730472580800 meters at the end of one year..

Similarly, we have some other light units too !

They are Light second, Light minute, Light hour, Light-day and Light week. Light-nanosecond and light-microsecond are used in telecommunication.

Example: Earth to sun distance is approximately 149,597,870,700 meters or just 8.32 light-minutes.

Other major unit that is used in astrophysics is “Astronomical unit or AU”. It is the the mean distance between earth and sun. Therefore, 1 AU equals 149,597,870,700 meters or 8.32 light-minutes.

That's all for this topic. I hope this helped you. Click here to read other topics or search your topic below.
Public image by NASA