One way or another, in our daily lives we measure distances: to the nearest supermarket, to the house of relatives in another city, to the
state border, and so on. However, when it comes to endless outer spaces, it turns out that the use of familiar values like kilometers is extremely irrational. And the point here is not only in the complexity of perception of the resulting gigantic values, but in the number of numbers in them. Even a spelling of so many zeros will become a problem. For example, from Mars to Earth, the shortest distance is 55.7 million kilometers. Six zeros! But the red planet is one of our closest neighbors in the sky. How to use bulky numbers that will be obtained when calculating the distance even to the nearest stars? And now we need such a quantity as light year. How much is he? Now let's figure it out.
What is 1 light year equal to?
The concept of light year is also closely related to relativistic physics, in which the close connection and mutual dependence of space and time was established at the beginning of the 20th century, when the postulates of Newtonian mechanics collapsed. To this distance, larger units in the system
formed quite simply: each subsequent one was a collection of units of a smaller order (centimeters, meters, kilometers, and so on). In the case of light year, the distance was tied to time. Modern science knows that the speed of light in a vacuum is constant. Moreover, it is the maximum speed in nature admissible in modern relativistic physics. These ideas were laid in the basis of the new meaning. A light year is the distance that a ray of light travels in one earth calendar year. In kilometers it is approximately 9.46 * 10
15 kilometers. It is interesting that to the nearest
celestial body, the moon, a photon travels a distance in 1.3 seconds. To the Sun - about eight minutes. But until the next nearest stars, Alpha and
Proxima Centauri, for about four light years.
Just a fantastic distance. There is an even larger measure of space in astrophysics. A light year is approximately one third of a parsec, an even larger unit of interstellar distance.
The speed of light in different conditions
By the way, there is also such a feature that photons can propagate at different speeds in different environments. We already know how fast they fly in a vacuum. And when they say that a light year is equal to the distance traveled by light in a year, they mean empty space. However, it is interesting to note that under other conditions the speed of light may be less. For example, in air, photons scatter at a slightly lower speed than in vacuum. Which one it depends on the particular state of the atmosphere. Thus, in a gas-filled environment, the light year would be equal to a slightly lower value. However, it would be insignificantly different from the accepted one.