Share our articles!
Light year
During the exploration of their planet, people needed various measures for measuring distances and segments. Initially, length measures were inaccurate because different nations there were their own ways of measuring. It was only in 1791 that 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 space exploration. And the fact that the Universe has incredible distances, already exists metric system turned out to be unsuitable for measuring such long 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, or even stars, the number will contain an incredible number of zeros.
And then scientists decided to introduce the term “light years”.
How many light years is that?
In just one second, photons of light travel a distance of 300 thousand 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 much?
We assume that the spacecraft flies from the third escape velocity(about 16.8 kilometers per second), then in 18 thousand years the ship will fly one light year. And our galaxy Milky Way, which is about one 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 you calculate it in kilometers, the figure turns out to be very large.
But if we compare the distance from Proxima Centauri to the nearest galaxy, the Andromeda Nebula, the star turns out to be very close, since Andromeda is located two and a half million light years from the Milky Way. Spaceship will be able to get there in 35 billion years.
What else are light years useful for?
Using light years helps us understand where in the universe we can try to find intelligent civilizations. This is how 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 a sent signal that will last at least one human life.
As you know, to measure the distances from the Sun to the planets, as well as between the planets, scientists came up with 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 the nearest stars, it became obvious that the astronomical unit was inconvenient for use in the stellar world. Let's say for starters that the distance from the Sun to 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 recalculated in astronomical units, it will be approximately 67,000. And this is only for 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.
It is this definition that is recommended for use in popular science literature. IN professional literature to express large distances instead light years Parsecs and multiples of units (kilo- and megaparsecs) are commonly used.
Previously (before 1984), a light year was the distance traveled by light in one tropical year, assigned to the epoch 1900.0. The new definition differs from the old one by approximately 0.002%. Since this distance unit is not used for high-precision measurements, practical difference there is no difference between old and new definitions.
Numeric values
A light year is equal to:
- 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 (exact)
- 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 qualitatively representing 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 a beam of light emitted from the surface of the Earth will take about 1.3 seconds to reach the surface of the Moon. |
| minutes | 1.6·10−5 | One astronomical unit is equal to approximately 150 million kilometers. Thus, light travels from the Sun to Earth in approximately 500 seconds (8 minutes 20 seconds). |
| Watch | 0,0006 | The average distance from the Sun to Pluto is approximately 5 light hours. |
| 0,0016 | Devices of the Pioneer and Voyager series flying beyond solar system, in about 30 years since the launch, they have moved to a distance of about one hundred astronomical units from the Sun, and their response time to requests from 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. It will take about a year and a half for light to travel the distance from the Sun to the outer edge of the cloud. |
| 2,0 | Maximum area radius gravitational influence Sun (“Hill Spheres”) - approximately 125,000 AU. e. | |
| 4,22 | The closest star to us (not counting the Sun), Proxima Centauri, is located at a distance of 4.22 light years. 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 closest spiral galaxy to us, 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 closest cluster of galaxies, the Virgo cluster, is 59 million light-years away. | |
| 1.5 10 8 - 2.5 10 8 | The “Great Attractor” gravitational anomaly 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. It will take about a billion years for light to travel from end to end. |
| 1.4 10 10 | The size of the causally connected region of the Universe. Calculated from the age of the Universe and maximum speed transmission of information - the speed of light. | |
| 4.57 10 10 | The accompanying distance from the Earth to the edge of the observable Universe in any direction; accompanying radius of the observable Universe (within the framework of the standard cosmological model Lambda-CDM). |
Galactic distance scales
- An astronomical unit with good accuracy is equal to 500 light seconds, that is, light reaches the Earth from the Sun in about 500 seconds.
see also
Links
- International Organization for Standardization. 9.2 Measurement units
Notes
Wikimedia Foundation. 2010.
See what “Light Year” is in other dictionaries:
An extra-system unit of length used in astronomy; 1 S.g. is equal to the distance traveled by light in 1 year. 1 S. g. = 0.3068 parsec = 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 distance, which light passes through outer space or in VACUUM for one tropical year. One light year is equal to 9.46071012 km... Scientific and technical encyclopedic dictionary
LIGHT YEAR, 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- LIGHT YEAR, 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
An extra-system 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. * * * LIGHT YEAR LIGHT YEAR, a unit of interstellar distances; the path that light travels in a year, i.e. 9.46×1012 km... encyclopedic Dictionary
Light year- a unit of distance equal to the path traveled by light in one year. A light year is equal to 0.3 parsecs... Concepts modern natural science. Glossary of basic terms
In order to understand the meaning of the concept of “light year”, you first need to remember school course physics, especially that section that concerns the speed of light. So, the speed of light in a vacuum, where it is not acted upon various factors, such as gravitational and magnetic fields, suspended particles, refraction of a transparent medium, etc., is 299,792.5 kilometers per second. You need to understand that in in this case by light we mean perceived human vision.
Less known units Distance measurements are light month, week, day, hour, minute and second.For quite a long time, 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-17th century century. Of course, his data were very approximate, but the very fact of determining the final speed value is important. In 1970, the speed of light was determined to within one meter per second. More accurate results have not yet been achieved, as problems arose with the error of the meter standard.
Light year and other distances
Since the distances are enormous, measuring them in conventional units would be irrational and inconvenient. Based on these considerations, a special one was introduced - the light year, that is, the distance that light travels in the so-called Julian year(equal to 365.25 days). Considering that every day contains 86,400 seconds, it can be calculated that in a year a ray of light travels a distance of slightly more than 9.4 kilometers. This value seems enormous, however, for example, the distance to the closest star to Earth, Proxima Centauri, is 4.2 years, and the diameter of the Milky Way galaxy exceeds 100,000 light years, that is, the visual observations that can be made now reflect a picture that existed about hundreds of thousands of years ago.
A ray of light travels the distance from the Earth to the Moon in about a second, but sunlight It takes more than eight minutes to reach our planet.
In professional astrophysics, the concept of a light year is rarely used. Scientists primarily use units such as parsec and astronomical unit. A parsec is the distance to the imaginary point from which the radius of the Earth's orbit is seen at an angle of one arcsecond (1/3600 of a degree). The average radius of the orbit, that is, the distance from the Earth to the Sun, is called the astronomical unit. A parsec is equal to approximately three light years or 30.8 trillion kilometers. An astronomical unit is approximately equal to 149.6 million kilometers.
For their calculations, astronomers use special units of measurement that are not always clear ordinary people. This is understandable, because if cosmic distances were measured in kilometers, then the number of zeros would dazzle the eyes. Therefore, to measure cosmic distances it is customary to use much large quantities: astronomical unit, light year and parsec.
Quite often used to indicate distances within our native Solar System. If we can also express it in kilometers (384,000 km), then Pluto is the closest close way is approximately 4,250 million km, and this will be difficult to understand. For such distances it is time to use an astronomical unit (AU), equal to the average distance from earth's surface to the Sun. In other words, 1 a.u. corresponds to the length of the semimajor axis of our Earth’s orbit (150 million km). Now, if we write that the shortest distance to Pluto is 28 AU, and the shortest long haul may be 50 AU, this is much easier to imagine.
The next largest is a light year. Although the word “year” is present there, one should not think that we're talking about about the time. One light year is 63,240 AU. This is the path that a ray of light travels over the course of 1 year. Astronomers have calculated that from the most distant corners of the Universe, a ray of light takes more than 10 billion years to reach us. To imagine this gigantic distance, let’s write it in kilometers: 95000000000000000000000. Ninety-five billion trillion usual kilometers.
Scientists began to guess that light does not travel instantly, but at a certain speed, starting in 1676. It was at this time that a Danish astronomer named Ole Roemer noticed that the eclipses of one of Jupiter's satellites were beginning to lag, and this happened precisely when the Earth was heading in its orbit towards opposite side The sun opposite to where Jupiter was. Some time passed, the Earth began to move back, and eclipses again began to approach their previous schedule.
Thus, about 17 minutes of time difference were noted. From this observation it was concluded that it took light 17 minutes to travel a distance the length of the Earth’s orbit. Since the diameter of the orbit was proven to be approximately 186 million miles (now this constant is 939,120,000 km), it turned out that the light beam moves at a speed of about 186 thousand miles per second.
Already in our time, thanks to Professor Albert Michelson, who set out to determine as accurately as possible what a light year is, using a different method the final result was obtained: 186,284 miles in 1 second (approximately 300 km/s). Now, if we count the number of seconds in a year and multiply by this number, we find that a light year is 5,880,000,000,000 miles long, which corresponds to 9,460,730,472,580.8 km.
For practical purposes, astronomers often use a unit of distance called the parsec. It is equal to the displacement of the star against the background of others celestial bodies by 1"" when the observer is shifted by 1 radius