Astronomy: What is a Light Year?

What is a light year?

The answer is very simple! A light year is a unit of measuring the distance, especially used in astronomy. As the distances between the stars, the galaxies are very huge and it is difficult to explain them in regular units of distances, the concept of light years was introduced.

The light travels about 300,000 Kilo Meters (Exactly saying 299,792.458 Kilo Meters) per second. So when we calculate, we find that it travels 9,500,000,000,000 Kilo Meters (That is about 10Trillions Kilo Meters or 6 Trillion Miles) in a year!This distance is known as One Light Year distance.

The nearest star to us is Proxima Centauri. It is just (!) 4.24 Light Years away from us. It means, the light coming from that star reach to us after 4.24 years. In other words, this distance is about 42 Trillions of Kilo Meters.

It also means that the star Proxima Centauri we see today, is of 4.24 years before.

Friedrich Wilhelm Bessel, inventor of the Light Year concept.
Friedrich Wilhelm Bessel, inventor of the Light Year concept.

Who Invented The Concept of Light Year?

Many people know the concept of a light year, but few people know that Friedrich Wilhelm Bessel, a German mathematician and astronomer, was the inventor and the first user of the light year concept in 1838.

He was born 22nd July 1784. He was lacking University education. In spite of that, he became a famous astronomer of his times. He was first to use Parallax to calculate the distance to stars. At the age of 26, he was appointed as director of the Königsberg Observatory by King Frederick William III of Prussia. There he recorded positions of over 50000 stars.

The asteroid 1552 and the largest crater in the Moon's Mare Serenitatis is named Bessel after this great astronomer.

Top 10 Nearest Stars


A list of top 10 nearest stars from us.

Proxima Centauri: 4.24 Light Years

Apha Centauri A : 4.36 Light Years

Apha Centauri B: 4.36 Light Years

Barnard's Star: 5.96 Light Years

Wolf 359: 7.78 Light Years

Lalande 21185: 8.29 Light Years

Sirius A: 8.58 Light Years

Sirius B: 8.58 Light Years

Luyten 726-8 A: 8.72 Light Years

Luyten 726-8 B: 8.72 Light Years

Sirius A and B stars, 8.72 Light Years away from us. Hubble photo.
Sirius A and B stars, 8.72 Light Years away from us. Hubble photo. | Source

Video: Light Years Explained0

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Comments 7 comments

rahul0324 profile image

rahul0324 4 years ago from Gurgaon, India

In other words we can say that the measurement of time in years which light takes to reach earth from other distant celestial bodies depends on the distance traveled by light per year...i.e directly proportional to it..

Great info Jain ...


Olde Cashmere profile image

Olde Cashmere 4 years ago from Michigan, United States

Really puts things into perspective. The universe is so mysterious and vast it's absolutely mind boggling. Thank you for an awesome hub jainismus. Voted up, shared, awesome, and interesting :)


jainismus profile image

jainismus 4 years ago from Pune, India Author

lone77star,

Thank you for adding some information.


ib radmasters profile image

ib radmasters 4 years ago from Southern California

lone77star

3.26 is pretty close to the value of Pi, also in the circle area.

Just an association, no real value.


ib radmasters profile image

ib radmasters 4 years ago from Southern California

The problem is that when you get to these stars, what are you going to do there?

In my opinion,the universe is an overkill, at least for us on Earth.

The limiting factor is human nature. No matter where we go we would do the same thing that we have down on Earth, since our existence began.


lone77star profile image

lone77star 4 years ago from Cebu, Philippines

And the other interstellar unit of measure is also based upon the orbit of the Earth: parsec (pc).

1 pc = ~3.26 light years


MarleneWheeler profile image

MarleneWheeler 4 years ago

Beam me up Scotty!

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