Surely, having heard in some fantastic action movie the expression a la “20 to Tatooine light years”, many asked legitimate questions. I will name some of them:

Isn't a year a time?

Then what is light year?

How many kilometers does it have?

How long will it take light year space ship with Earth?

I decided to dedicate today's article to explaining the meaning of this unit of measurement, comparing it with our usual kilometers and demonstrating the scales that Universe.

Virtual Racer.

Imagine a person, in violation of all the rules, rushing along the highway at a speed of 250 km / h. In two hours he will overcome 500 km, and in four - as many as 1000. Unless, of course, he crashes in the process ...

It would seem that this is the speed! But in order to circumnavigate the entire globe (≈ 40,000 km), our rider 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. Since laziness has always forced us to invent and use shorter alternative units of measurement.

Limit.

From a school physics course, everyone should know that the fastest rider in Universe- light. In one second, its beam covers a distance of approximately 300,000 km, and the globe, thus, it will go around in 0.134 seconds. That's 4,298,507 times faster than our virtual racer!

From Earth before Moon light reaches on average in 1.25 s, up to sun its beam will rush 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. Therefore, the scientific world decided that it would be logical to measure cosmic scales in units that a radio wave passes over certain time intervals (which light, in particular, is).

Distances.

Thus, light year- nothing more than the distance that a ray of light overcomes in one year. On interstellar scales, using distance units smaller than this does not make much sense. And yet they are. 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.

And 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. Light travels 300,000 km in one second. Consequently, 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 SIXTY BILLION AND EIGHT HUNDRED MILLION kilometers.

Of course, the exact value light year slightly different from what we calculated. But when describing distances to stars in popular science articles, the highest accuracy is in principle not needed, and a hundred or two million kilometers will not play a special role here.

Now let's continue our thought experiments...

Scales.

Let's assume modern spaceship leaves solar system with the third space velocity (≈ 16.7 km/s). First light year he will overcome in 18,000 years!

4,36 light years to our nearest star system ( Alpha Centauri, see the image at the beginning) it will overcome in about 78 thousand years!

Our the Milky Way galaxy, having a diameter of approximately 100,000 light years, it will cross in 1 billion 780 million years.

And to the nearest one to us galaxies, spaceship rushing only after 36 billion years ...

These are the pies. But in theory, even Universe arose only 16 billion years ago ...

And finally...

You can start to wonder at the cosmic scale even without going beyond solar system because it is very large in itself. This was shown very well and clearly, for example, by the creators of the project If the Moon wereonly 1 pixel (If the moon were just one pixel): http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html .

On this I, perhaps, will complete today's article. All your questions, comments and wishes are welcome in the comments below it.

Do you know why astronomers don't use the light year to calculate distances to distant objects in space?

A light year is a non-systemic unit for measuring distances in outer space. It is ubiquitous in popular books and textbooks on astronomy. However, in professional astrophysics, this figure is used extremely rarely and often to determine distances to nearby objects in space. The reason for this is simple: if you determine the distance in light years to distant objects in the Universe, the number will be so huge that it will be impractical and inconvenient to use it for physical and mathematical calculations. Therefore, instead of a light year, professional astronomy uses such a unit of measurement as , which is much more convenient to operate when performing complex mathematical calculations.

Definition of the term

We can find the definition of the term "light year" in any astronomy textbook. A light year is the distance that a ray of light travels in one Earth year. Such a definition may satisfy the amateur, but the cosmologist will find it incomplete. He will notice that a light year is not just the distance that light travels in a year, but the distance that a beam of light travels in 365.25 Earth days in vacuum, without being affected by magnetic fields.

A light year is 9.46 trillion kilometers. This is the distance a ray of light travels in a year. But how did astronomers achieve such an accurate determination of the ray path? We will talk about this below.

How is the speed of light determined?

In ancient times, it was believed that light propagates in the universe instantly. However, beginning in the seventeenth century, scholars began to doubt this. Galileo was the first to doubt the above proposed statement. It was he who tried to determine the time during which a ray of light travels a distance of 8 km. But due to the fact that such a distance was negligible for such a value as the speed of light, the experiment ended in failure.

The first major shift in this issue was the observation of the famous Danish astronomer Olaf Römer. In 1676, he noticed the difference in the time of an eclipse depending on the approach and removal of the Earth to them in outer space. Roemer successfully connected this observation with the fact that the farther the Earth moves away from, the more time it takes for the light reflected from them to travel the distance to our planet.

Roemer caught the essence of this fact exactly, but he did not succeed in calculating the reliable value of the speed of light. His calculations were wrong, because in the seventeenth century he could not have accurate data on the distance from the Earth to other planets in the solar system. These data were determined somewhat later.

Further advances in research and determination of the light year

In 1728, the English astronomer James Bradley, who discovered the effect of stellar aberration, was the first to calculate the approximate speed of light. He determined its value at 301 thousand km / s. But this value was inaccurate. More advanced methods for calculating the speed of light were produced independently of cosmic bodies - on Earth.

Observations of the speed of light in vacuum using a rotating wheel and a mirror were made by A. Fizeau and L. Foucault, respectively. With their help, physicists managed to get closer to the real value of this quantity.

Accurate speed of light

Scientists managed to determine the exact speed of light only in the last century. Based on Maxwell's theory of electromagnetism, using modern laser technology and calculations, corrected for the refractive index of the ray flux in air, scientists were able to calculate the exact value of the speed of light 299,792.458 km/s. This value is still used by astronomers. Further, to determine the light day, month and year was already a matter of technology. By simple calculations, scientists got the figure of 9.46 trillion kilometers - that is how much time it would take for a beam of light to fly around the length of the earth's orbit.

Off-system unit of length used in astronomy; 1 S. g. is equal to the distance traveled by light in 1 year. 1 S. g. \u003d 0.3068 parsec \u003d 9.4605 1015 m. Physical encyclopedic dictionary. Moscow: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. ... ... Physical Encyclopedia

LIGHT YEAR, a unit of astronomical distance, equal to the distance that light travels in open space or in VACUUM in one tropical year. One light year is equal to 9.46071012 km... Scientific and technical encyclopedic dictionary

LIGHTYEAR, a unit of length used in astronomy: the path traveled by light in 1 year, i.e. 9.466?1012 km. The distance to the nearest star (Proxima Centauri) is approximately 4.3 light years. The most distant stars in the Galaxy are located on ... ... Modern Encyclopedia

Unit of interstellar distances; the path that light travels in a year, i.e. 9.46 × 1012 km ... Big Encyclopedic Dictionary

Light year- LIGHTYEAR, a unit of length used in astronomy: the path traveled by light in 1 year, i.e. 9.466´1012 km. The distance to the nearest star (Proxima Centauri) is approximately 4.3 light years. The most distant stars in the Galaxy are located on ... ... Illustrated Encyclopedic Dictionary

A non-systemic unit of length used in astronomy. 1 light year is the distance that light travels in 1 year. 1 light year is equal to 9.4605E+12 km = 0.307 pc... Astronomical dictionary

Unit of interstellar distances; the path that light travels in a year, that is, 9.46 1012 km. * * * LIGHTYEAR LIGHTYEAR, a unit of interstellar distances; the path that light travels in a year, i.e. 9.46x1012 km ... encyclopedic Dictionary

Light year- a unit of distance equal to the path traveled by light in one year. A light year is 0.3 parsec... Concepts of modern natural science. Glossary of basic terms

light year- šviesmetis statusas T sritis Standartizacija ir metrologija apibrėžtis Astronominis ilgio matavimo vienetas, lygus nuotoliui, kurį vakuume nusklinda šviesa per 1 atogrąžinius metus. Žymimas šm: 1 šm = 9.46073 10¹² km. atitikmenys: engl. light… … Penkiakalbis aiskinamasis metrologijos terminų žodynas

light year- šviesmetis statusas T sritis fizika atitikmenys: angl. light year vok. Lichtjahr, n rus. light year, m pranc. année lumière, f … Fizikos terminų žodynas

Books

• There is no way back. Set of 3 books, Lukyanov Alexey, Naumov Ivan Sergeevich. Set of 3 books. 1. "Tsunami. Book One. Earthshakers" 1999. Egor and Yusya Kruglov are left without adult care. Nothing good lies ahead for them. Disability has made...
• Fascinating astronomy, Elena Kachur. About the book In the new and long-awaited book, Chevostik and Uncle Kuzya go to the observatory! Here they will have a fascinating acquaintance with the heavenly bodies that adorn our night sky. Together with…

Galactic distance scales

Light year ( St. G., ly) is an off-system unit of length equal to the distance traveled by light in one year.

More precisely, according to the definition of the International Astronomical Union (IAU), a light year is equal to the distance that light travels in vacuum, without being affected by gravitational fields, in one Julian year (which is equal by definition to 365.25 standard days of 86,400 SI seconds, or 31,557 600 seconds). It is this definition that is recommended for use in popular science literature. In professional literature, parsecs and multiples of units (kilo- and megaparsecs) are usually used instead of a light year to express large distances.

Previously (until 1984), a light year was the distance traveled by light in one tropical year, referred to the 1900.0 epoch. The new definition differs from the old one by about 0.002%. Since this unit of distance is not used for highly accurate measurements, there is no practical difference between the old and new definitions.

Numeric values

A light year is:

• 9 460 730 472 580 800 meters (approximately 9.46 petameters)
• 63,241.077 astronomical units (AU)
• 0.306601 parsecs

Related units

The following units are used quite rarely, usually only in popular publications:

• 1 light second = 299,792.458 km (exactly)
• 1 light minute ≈ 18 million km
• 1 light hour ≈ 1079 million km
• 1 light day ≈ 26 billion km
• 1 light week ≈ 181 billion km
• 1 light month ≈ 790 billion km

Distance in light years

The light year is convenient for qualitative representation of distance scales in astronomy.

One way or another, in our daily life we ​​measure distances: to the nearest supermarket, to the house of relatives in another city, to and so on. However, when it comes to the vast expanses of space, it turns out that the use of familiar values ​​​​like kilometers is extremely irrational. And the point here is not only the difficulty of perceiving the resulting gigantic values, but the number of digits 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 will be obtained when calculating the distance even to the nearest stars? And right now we need such a value as a light year. How much is he? Now let's figure it out.

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 of Newtonian mechanics collapsed. Before this distance value, the larger units in the system

were formed quite simply: each subsequent one was a set of units of a smaller order (centimeters, meters, kilometers, and so on). In the case of a 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 allowed in modern relativistic physics. It was these ideas that formed the basis of the new meaning. A light year is equal to the distance that a ray of light travels in one Earth calendar year. In kilometers, this is approximately 9.46 * 10 15 kilometers. Interestingly, to the nearest moon, a photon travels the distance in 1.3 seconds. To the Sun - about eight minutes. But to the next nearest stars, Alpha, and already about four light years.

Just a fantastic distance. There is an even larger measure of space in astrophysics. A light year is about one-third of a parsec, an even larger unit of measurement for interstellar distances.

The speed of light propagation 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 precisely empty outer 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. With which one - depends on the specific state of the atmosphere. Thus, in a gas-filled medium, a light year would be somewhat smaller. However, it would not differ significantly from the accepted one.