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Light year
During the exploration of their planet, people needed various measures of measuring distances and segments. Initially, length measures were inaccurate, because different peoples had their own ways of measuring. Only in 1791, scientists from France introduced a measure that is still used today - the meter (from the Greek - "measure").
But at the beginning of the twentieth century, people began to turn their attention to the study of space. And the fact that the universe has incredible distances already exists metric system turned out to be unsuitable for measuring such large distances. It is possible to measure in kilometers the distance from our planet to the Moon or to Mars, but if you measure the distances to other planets, and even stars, then there will be an incredible number of zeros in the figure.
And then scientists decided to introduce the term "light years".
How many light years?
In just one second, photons of light cover a length of 300,000 km. A light year is the number of kilometers that light travels in 12 months. In kilometers it will be - 9,460,730,472,580.8 kilometers ≈ 9.46 1015.
Of course, using the term "light years" is more convenient than using huge kilometers. But, of course, there are approximate values:
1 light second ≈ 300 thousand kilometers.
1 light minute ≈ 18 million kilometers.
1 light hour ≈ 1,080,000,000 kilometers.
1 light day ≈ 26,000,000,000 kilometers.
1 light week ≈ 181,000,000,000 kilometers.
1 light month ≈ 790,000,000,000 kilometers.
How many?
We assume that the spacecraft flies from the third space speed(about 16.8 kilometers per second), then in 18 thousand years the ship will fly one light year. And our galaxy the Milky Way, which is about a hundred thousand light years in diameter, the ship will fly by in almost 2 billion years!
The closest star to the Sun is Proxima Centauri. It is located at a distance of about four light years. If converted to kilometers, the figure is very large.
But if we compare the distance from Proxima Centauri to the nearest galaxy, the Andromeda Nebula, then the star is very close, since Andromeda is two and a half million light-years from the Milky Way. Spaceship can fly there in 35 billion years.
What else are light years useful for?
Using light years helps you understand where in the universe you can try to find intelligent civilizations. So scientists determine where it makes sense to send radio signals, and where not.
How it works: the speed of light is equal to the speed of a radio signal, and it turns out that sending messages to where they will reach in thousands, or even billions of years, is completely useless. It makes sense to look for "neighbors" through the sent signal, which will go on for at least one human life.
Anyway, in your Everyday 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 close connection and the 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 light year distance was tied to time. modern science We know that the speed of light in 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 the distance 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 distance, overcome by light per year, they mean exactly empty outer space. However, it is interesting to note that under other conditions the speed of light may be less. For example, in air environment photons scatter at a slightly lower speed than in vacuum. Which one - depends on specific state atmosphere. Thus, in a gas-filled medium, a light year would be somewhat smaller. However, it would not differ significantly from the accepted one.
In order to understand the meaning of the concept of "light year", you first need to remember school course physics, especially the section that deals with the speed of light. So the speed of light in a vacuum, where it is not affected various factors, such as gravity and magnetic fields, suspended particles, refraction of a transparent medium, etc., is 299,792.5 kilometers per second. It must be understood that in this case light means perceived human vision.
Less known units distance measurements are light month, week, day, hour, minute and second.Long enough light was considered an infinite quantity, and the first person to calculate the approximate speed of light rays in a vacuum was the astronomer Olaf Roemer in mid-seventeenth century. Of course, his data were very approximate, but the very fact of determining final value speed. In 1970, the speed of light was determined to within one meter per second. More accurate results have not been achieved so far, as there were problems with the error of the meter standard.
Light year and other distances
Since the distances in are huge, measuring them in customary units would be irrational and inconvenient. Based on these considerations, a special light year was introduced, that is, the distance that light travels in the so-called julian year(equal to 365.25 days). Considering that each day contains 86,400 seconds, it can be calculated that in a year a ray of light covers a distance of several more than 9.4 kilometers. This value seems huge, however, for example, the distance to the nearest star to the Earth, Proxima Centauri, is 4.2 years, and the diameter of the Milky Way galaxy exceeds 100,000 light years, that is, those visual observations that can be made now display a picture that existed about hundreds of thousands of years ago.
A beam of light covers the distance from the Earth to the Moon in about a second, but sunlight reaches our planet for more than eight minutes.
In professional astrophysics, the concept of a light year is rarely used. Scientists mainly operate with units such as the parsec and the astronomical unit. A parsec is the distance to an imaginary point from which the radius of the Earth's orbit is seen at an angle of one arc second (1/3600 of a degree). Medium radius orbit, that is, the distance from the Earth to the Sun, is called the astronomical unit. A parsec is about 3 light years or 30.8 trillion kilometers. An astronomical unit is approximately equal to 149.6 million kilometers.
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 light year?
First of all, it should be noted that a light year is also a unit of measurement adopted in astronomy, but not of time (as it may seem, judging by the meaning of the word “year”), but of distance.
What is a light year
When scientists were able to calculate the distances to the nearest stars, it became obvious that in the stellar world the astronomical unit was inconvenient for use. Let's say for starters that the distance from the Sun to the nearest star is about 4.5 light years. This means that the light from our Sun to the nearest star (it is called, by the way, Proxima Centauri) flies 4.5 years! How big is this distance? We will not bore anyone with mathematics, we will only 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 the Earth in 8.5 minutes. And how much then do the rays of light fly by in a year?
Let's just say: a light year is about 10 trillion kilometers(a trillion is a one followed by twelve zeros). More precisely, 9,460,730,472,581 kilometers. If counted in astronomical units ah, that would be about 67,000. And that's just 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 polar star is about 600 light years. That is, the light from us gets there for 600 years. It will be approximately 40 million astronomical units. For comparison, we indicate that the size (diameter) of our Galaxy is milky way- about 100,000 light years. Our closest neighbor spiral galaxy, called the Andromeda Nebula, is 2.52 million light-years distant from Earth. It is very inconvenient to state this in astronomical units. But there are objects in the Universe that are 15 billion light-years distant from us. Thus, the radius of the observable universe is 13.77 billion light years. BUT complete universe, as is known, extends beyond the observed part.
By the way, the diameter of the observable universe is not at all 2 times more radius as you might think. The point is that space expands over time. Those distant objects that emitted light 13.77 billion years ago flew even further away from us. Today they are more than 46.5 billion light-years away. Doubling that, we get 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.
It makes no sense to measure such distances in kilometers or astronomical units. To be honest, light years don't quite fit here either. But nothing better people not yet figured out. The numbers are so huge that only a computer can handle them.
Definition and essence of the light year
In this way, a light year (st. g.) is a unit of length, not time, which is the distance traveled sunbeam for a year, i.e. for 365 days. This unit of measurement is very convenient for its clarity. It allows you to answer the question, after what period of time you can expect a response if you send an electromagnetic message to a certain star. And if this period is too long (for example, it is a thousand years), then there is no point in such actions.
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 to express large distances instead of a light year.
Previously (until 1984), a light year was the distance traveled by light in one tropical year, referred to the epoch 1900.0. 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 9.5 petameters)
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.
| Scale | Value (st. years) | Description |
|---|---|---|
| Seconds | 4 10 −8 | The average distance to the Moon is approximately 380,000 km. This means that it takes about 1.3 seconds for a beam of light emitted from the surface of the Earth to reach the surface of the Moon. |
| minutes | 1.6 10 −5 | One astronomical unit equals approximately 150 million kilometers. Thus, light travels from the Sun to the Earth in about 500 seconds (8 minutes 20 seconds). |
| Watch | 0,0006 | The average distance from the Sun to Pluto is approximately 5 light hours. |
| 0,0016 | Pioneer and Voyager series vehicles flying beyond solar system, about 30 years after launch, have moved to a distance of about one hundred astronomical units from the Sun, and their response time to requests from the Earth is approximately 14 hours. | |
| Year | 1,6 | The inner edge of the hypothetical Oort cloud is located at 50,000 AU. e. from the Sun, and the outer one - 100,000 a. e. To cover the distance from the Sun to the outer edge of the cloud, the light will take about one and a half years. |
| 2,0 | Maximum Area Radius gravitational influence Sun ("Hill's Spheres") - approximately 125,000 a. e. | |
| 4,22 | The closest star to us (not counting the Sun), Proxima Centauri, is located at a distance of 4.22 sv. of the year . | |
| Millennium | 26 000 | The center of our Galaxy is approximately 26,000 light-years from the Sun. |
| 100 000 | The diameter of the disk of our galaxy is 100,000 light years. | |
| Millions of years | 2.5 10 6 | The nearest spiral galaxy M31, the famous Andromeda galaxy, is 2.5 million light-years away. |
| 3.14 10 6 | The Triangulum Galaxy (M33) is located 3.14 million light-years away and is the most distant stationary object visible to the naked eye. | |
| 5.9 10 7 | The nearest cluster of galaxies, the Virgo cluster, is 59 million light-years away. | |
| 1.5 10 8 - 2.5 10 8 | The gravitational anomaly "Great Attractor" is located at a distance of 150-250 million light years from us. | |
| Billions of years | 1.2 10 9 | The Great Wall of Sloan is one of the largest formations in the Universe, its dimensions are about 350 Mpc. For light to overcome it from end to end, it will take about a billion years. |
| 1.4 10 10 | The size of a causally connected region of the universe. Calculated from the age of the universe and top speed transmission of information - the speed of light. | |
| 4.57 10 10 | The comoving distance from Earth to the edge of the observable universe in any direction; the comoving radius of the observable Universe (within the framework of the standard Lambda-CDM cosmological model). |
Galactic distance scales
- An astronomical unit with good accuracy is equal to 500 light seconds, that is, light travels from the Sun to the Earth in about 500 seconds.
see also
Links
- International Organization for Standardization. 9.2 Measurement units
Notes
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See what "light year" is in other dictionaries:
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. M.: Soviet Encyclopedia. Chief Editor A. M. Prokhorov. ... ... Physical Encyclopedia
LIGHT YEAR, unit of measurement astronomical distance, equal to the distance, which the light passes through open space or in VACUUM for 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- unit of distance, equal path traveled by light in one year. A light year is 0.3 parsec... Concepts modern natural science. Glossary of basic terms
