Exploring their own planet, over hundreds of years, people invented more and more new systems for measuring distance segments. As a result, it was decided to consider universal unit one meter long and big way measured in kilometers.
But the advent of the twentieth century confronted humanity with new problem. People began to carefully study space - and it turned out that the vastness of the Universe is so vast that kilometers are simply not suitable here. In conventional units you can still express the distance from the Earth to the Moon or from the Earth to Mars. But if you try to determine how many kilometers the nearest star is from our planet, the number “overgrows” with an unimaginable number of decimal places.
What is 1 light year equal to?
It became obvious that a new unit of measurement was needed to explore the spaces of space - and the light year became it. In one second, light travels 300,000 kilometers. Light year - this is the distance that light will travel in exactly one year - and translated into a more familiar number system, this distance is equal to 9,460,730,472,580.8 kilometers. It is clear that using the laconic “one light year” is much more convenient than using this huge figure in calculations every time.
Of all the stars, Proxima Centauri is closest to us - it is “only” 4.22 light years away. Of course, in terms of kilometers the figure will be unimaginably huge. However, everything can be learned by comparison - if we consider that nearest galaxy called Andromeda is a whopping 2.5 million light years away from the Milky Way, the aforementioned star is indeed beginning to seem like a very close neighbor.
By the way, using light years helps scientists understand in which corners of the Universe it makes sense to look intelligent life, and where to send radio signals is completely useless. After all, the speed of a radio signal is similar to the speed of light - accordingly, a greeting sent towards a distant galaxy will reach its destination only after millions of years. It is more reasonable to expect an answer from closer “neighbors” - objects whose hypothetical response signals will reach earthly devices at least during a person's life.
1 light year is how many Earth years?
There is a widespread misconception that the light year is a unit of time. In fact, this is not true. The term has nothing to do with earthly years, does not correlate with them in any way and refers exclusively to the distance that light travels in one earthly year.
One way or another, in my Everyday life we measure distances: to the nearest supermarket, to a relative’s house in another city, to and so on. However, when it comes to the vastness of outer space, it turns out that using familiar values like kilometers is extremely irrational. And the point here is not only in the difficulty of perceiving the resulting gigantic values, but in the number of numbers in them. Even writing so many zeros will become a problem. For example, the shortest distance from Mars to Earth is 55.7 million kilometers. Six zeros! But the red planet is one of our closest neighbors in the sky. How to use the cumbersome numbers that result when calculating the distance even to the nearest stars? And right now we need such a value as a light year. How much is it equal? Let's figure it out now.
The concept of a 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 collapsed Newtonian mechanics. Before this distance value, larger scale units in the system
were formed quite simply: each subsequent one was a collection of units of a smaller order (centimeters, meters, kilometers, and so on). In case light years distance was tied to time. Modern science It is known that the speed of light propagation in a vacuum is constant. Moreover, she is maximum speed in nature, acceptable in modern relativistic physics. It was these ideas that formed the basis of the new meaning. Light year equal to the distance, which a ray of light travels in one earthly calendar year. In kilometers it is approximately 9.46 * 10 15 kilometers. Interestingly, a photon travels the distance to the nearest Moon in 1.3 seconds. It's about eight minutes to the sun. But the next closest stars, Alpha, are already about four light years away.
Just a fantastic distance. There is an even larger measure of space in astrophysics. A light year is equal to about one-third of a parsec, an even larger unit of measurement of interstellar distances.
Speed of light propagation under different conditions
By the way, there is also such a feature that photons can at different speeds spread 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 covered by light in a year, they mean exactly the empty space. However, it is interesting to note that under other conditions the speed of light may be lower. For example, in air environment photons scatter at a slightly lower speed than in a vacuum. Which one depends on the specific state of the atmosphere. Thus, in a gas-filled environment, the light year would be somewhat smaller. However, it would not differ significantly from the accepted one.
As you know, to measure the distances from the Sun to the planets, as well as between the planets, scientists came up with an astronomical unit. What is it light year?
First of all, it should be noted that the light year is also a unit of measurement adopted in astronomy, but not of time (as it might seem, judging by the meaning of the word “year”), but of distance.
What is a light year equal to?
When scientists managed to calculate the distances to to the nearest stars, it became obvious that in the stellar world the astronomical unit is inconvenient for use. Let's say for starters that the distance from the Sun to the nearest star is approximately 4.5 light years. This means that light from our Sun to the nearest star (by the way, it is called Proxima Centauri) takes 4.5 years to travel! How far is this distance? Let’s not bore anyone with mathematics, let’s just note that in a second, particles of light fly 300,000 kilometers. That is, if you send a signal with a flashlight towards the Moon, this light will be seen there in less than a second and a half. Light travels from the Sun to Earth in 8.5 minutes. How long then do the rays of light travel in a year?
Let's say right away: a light year is approximately 10 trillion kilometers(a trillion is one followed by twelve zeros). More precisely, 9,460,730,472,581 kilometers. If converted to astronomical units, then it will be approximately 67,000. And this is only to the nearest star!
It is clear that in the world of stars and galaxies the astronomical unit is not suitable for measurements. It is easier to operate in calculations with light years.
Applicability in the stellar world
For example, the distance from Earth to the brightest star in the sky, Sirius, is 8 light years. And the distance from the Sun to North Star is about 600 light years. That is, light from us gets there in 600 years. This would be approximately 40 million astronomical units. For comparison, we point out that the size (diameter) of our Galaxy - the Milky Way - is about 100,000 light years. Our closest neighbor is spiral galaxy, which is called the Andromeda Nebula, is distant from Earth at a distance of 2.52 million light years. It is very inconvenient to indicate this in astronomical units. But there are objects in the Universe that are generally 15 billion light years away from us. Thus, the radius of the observable Universe is 13.77 billion light years. A complete universe, as is known, extends beyond the observable part.
By the way, the diameter of the observable Universe is not 2 times at all greater than radius, as you might think. The thing is that over time, space expands. Those distant objects that emitted light 13.77 billion years ago have flown even further away from us. Today they are more than 46.5 billion light years away. Doubling this gives us 93 billion light years. This is the true diameter of the observable Universe. So the size of the part of space that is being observed (and which is also called the Metagalaxy) is increasing all the time.
Measuring such distances in kilometers or astronomical units makes no sense. To be honest, light years don’t quite fit here either. But nothing better people haven't figured it out yet. The numbers are so huge that only a computer can handle them.
Definition and essence of light year
Thus, light year (light year) is a unit of length, not time, that represents the distance traveled sunbeam per year, that is, 365 days. This unit of measurement is very convenient for its clarity. It allows you to answer the question, after what period of time can you expect an answer if you send electromagnetic message. And if this period is too long (for example, a thousand years), then there is no point in such actions.
Surely, having heard in some science fiction action movie an expression a la “twenty to Tatooine light years", many asked legitimate questions. I'll mention some of them:
Isn't a year a time?
Then what is it light year?
How many kilometers is it?
How long will it take to overcome light year spaceship With Earth?
I decided to devote today’s article to explaining the meaning of this unit of measurement, comparing it with our usual kilometers and demonstrating the scale that it operates Universe.
Virtual racer.
Let's imagine a person, in violation of all the rules, rushing along a highway at a speed of 250 km/h. In two hours it will cover 500 km, and in four – as much as 1000. Unless, of course, it crashes in the process...
It would seem that this is speed! But in order to go around the whole Earth(≈ 40,000 km), our racer will need 40 times more time. And this is already 4 x 40 = 160 hours. Or almost a whole week of continuous driving!
In the end, however, we will not say that he covered 40,000,000 meters. Because laziness has always forced us to invent and use shorter alternative units of measurement.
Limit.
From school course physicists, everyone should know that the fastest rider in Universe- light. In one second, its beam covers a distance of approximately 300,000 km, and thus it will circle the globe in 0.134 seconds. That's 4,298,507 times faster than our virtual racer!
From Earth before Moon the light reaches on average 1.25 s, up to Sun its beam will reach in a little more than 8 minutes.
Colossal, isn't it? But the existence of speeds greater than the speed of light has not yet been proven. That's why scientific world I decided that it would be logical to measure cosmic scale in units that a radio wave passes over certain time intervals (which is what light, in particular, is).
Distances.
Thus, light year- nothing more than the distance that a ray of light travels in one year. On interstellar scales, it is not appropriate to use distance units smaller than this special meaning. And yet they are there. Here are their approximate values:
1 light second≈ 300,000 km;
1 light minute ≈ 18,000,000 km;
1 light hour ≈ 1,080,000,000 km;
1 light day ≈ 26,000,000,000 km;
1 light week ≈ 181,000,000,000 km;
1 light month ≈ 790,000,000,000 km.
Now, so that you understand where the numbers come from, let’s calculate what one is equal to light year.
There are 365 days in a year, 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute. Thus, a year consists of 365 x 24 x 60 x 60 = 31,536,000 seconds. In one second, light travels 300,000 km. Therefore, in a year its beam will cover a distance of 31,536,000 x 300,000 = 9,460,800,000,000 km.
This number reads like this: NINE TRILLION, FOUR HUNDRED AND SIXTY BILLION AND EIGHT HUNDRED MILLION kilometers.
Certainly, exact value light years slightly different from what we calculated. But when describing distances to stars in popular science articles highest precision in principle, it is not needed, and a hundred or two million kilometers will not play a special role here.
Now let's continue our thought experiments...
Scale.
Let's assume that modern spaceship leaves solar system from the third escape velocity(≈ 16.7 km/s). First light year he will overcome it in 18,000 years!
4,36 light years to the one closest to us star system (Alpha Centauri, see the image at the beginning) it will overcome in about 78 thousand years!
Our galaxy Milky Way , having a diameter of approximately 100,000 light years, it will cross in 1 billion 780 million years.
