I read the definition of light year as the distance travelled by light in free space in one year is called light year. Is this correct or not?
It is correct
A light-year is a unit of distance. It is the distance that light can travel in one year through vacuum. Light moves at a velocity of about 300,000 kilometres(km) each second. So in one year, it can travel about 10 trillion km. More p recisely, one light-year is equal to 9,500,000,000,000 kilometers.
Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy’s the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.
It is correct
A light-year is a unit of distance. It is the distance that light can travel in one year through vacuum. Light moves at a velocity of about 300,000 kilometres(km) each second. So in one year, it can travel about 10 trillion km. More p recisely, one light-year is equal to 9,500,000,000,000 kilometers.
Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy’s the Andromeda Galaxy, is 21 quintillion km. That's 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.
