Light years is one of The sensing distance is the more computing relevant to cosmology and astronomy goes to work. Light years is defined as a distance that light in a vacuum in a period of one year during the.

In this definition, two factors, the speed of light in vacuum, and the duration of a year involved. Now, duration the exact time of the year that have to calculate the amount of light years is used for the international definition is not only a recommendation letter based on the use of Roman years (time, Tai) by the International Union of astronomy is presented.

based on this recommendation, a year is equal to 365, the 25 days that each day, equivalent to 86., the 400 h. that, with a total definition of the speed of light to the amount of 299 to. 792 in. 458 km per second, the distance light years, equivalent to 9،460،730،472،580،800 the meter will be.

due to the lacking standard definition of year., exact and specialized season, a little less than this unit can be used, and the unit parsec is preferred. But in applications. light years more to the work that goes sometimes, assuming each year is equivalent to 365 days, and the speed of light, the equivalent of 300،000 km per SEC., the amount of light years it's almost equal to 1015 × 9. the 461 km fall.

can be a simple example for this definition to work. for example, when called, x is about 5 million light years with the Earth distance. means that 5 million years ago from this, the optical emitted that after 5 million years to Earth reached, and we, After 5 million years it light, we've seen and to the existence of such a star could go. What is this, now, is gone and we have 5 million years later, can understand.

of course, according to special relativity , this is a very long time, for us, is unnoticeable, but for your light, such a time does not make sense and the distance is very high, at time zero, during.