Galactic distance scales
Light year ( St. G., ly) is an extra-system unit of length equal to the distance traveled by light in one year.
More precisely, as defined by the International Astronomical Union (IAU), a light year is equal to the distance that light travels in a vacuum, unaffected by gravitational fields, in one Julian year (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 light years to express large distances.
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 unit of distance is not used for high-precision measurements, there is no practical difference between the old and new definitions.
Numeric values
A light year is equal to:
- 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 (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 is approximately 380,000 km. This means that a beam of light emitted from the surface 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 reaches the Earth in approximately 500 seconds (8 minutes 20 seconds). |
| Watch | 0,0006 | The average distance from the Sun is approximately 5 light hours. |
| 0,0016 | The devices of the Pioneer and series flying beyond, in about 30 years since the 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 is located at 50,000 a. 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 | The maximum radius of the region of gravitational influence of the Sun (“Hill Spheres”) is approximately 125,000 AU. e. | |
| 4,2 | The closest one to us (not counting the Sun), Proxima Centauri, is located at a distance of 4.2 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 our disk is 100,000 light years. | |
| Millions of years | 2.5 10 6 | The closest M31 to us, the famous one, is 2.5 million light years away from us. |
| 3.14 10 6 | (M33) is located 3.14 million light years away and is the most distant stationary object visible to the naked eye. | |
| 5.8 10 7 | The closest one, the Virgo cluster, is 58 million light years away from us. | |
| Tens of millions of light years | The characteristic size of galaxy clusters by diameter. | |
| 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 world, 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). |
“The search for life has begun,” says Guillem Anglada-Escudé, an astronomer at the University of London and Mary and leader of the Pale Red project team. Dot ("Pale red dot") who made the discovery.
The first excursion to a neighboring potentially habitable world could be carried out, within the framework of which it is planned to develop the concept of a fleet of spacecraft using light sails to move around the Galaxy. Another option is to send to Proxima b first. However, we are getting ahead of ourselves for now, inspired by the discovery we are rushing to the stars. But let's get back to the opening.
Today it is known that Proxima b orbits its red dwarf star (it is smaller and dimmer than the Sun) in 11 Earth days. The exoplanet is classified as rocky (has a hard surface) and is slightly larger than Earth in mass - at least 1.3 times. It is the closest exoplanet to us and possibly the closest to the solar system heavenly body, on which life can exist.
Note that the cold star in the constellation Centaurus is too dim to be seen with the naked eye. It is located adjacent to the much brighter double star Alpha Centauri AB.
“, and much more remains to be discovered. But the search for the closest possible analogue of Earth and the success of these searches have become the main thing in life for all of us. Now the next stage of work lies ahead - the search for life on the planet Proxima b,” concludes Anglada-Escudé.
To some extent, the discovery of such an exoplanet can be considered the beginning of a new stage in astronomical research.
"The discovery helps us set a new goal - building a generation of tracking telescopes that will allow us to study new worlds, and perhaps one day visit them. This is exactly what we needed to take exoplanet science to the next level." new level"says David Kipping of Columbia University in New York.
Do you know why astronomers don't use light years to calculate distances to distant objects in space?
A light year is a non-systemic unit of measurement of distances in outer space. It is widely used in popular books and textbooks on astronomy. However, in professional astrophysics this figure is used extremely rarely and is often used 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 turn out to be so huge that it will be impractical and inconvenient to use it for physical and mathematical calculations. Therefore, instead of the light year in professional astronomy, a unit of measurement is used, 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 a ray of light travels in one Earth year. Such a definition may satisfy an amateur, but a cosmologist will find it incomplete. He will note that a light year is not just the distance that light travels in a year, but the distance that a ray of light travels in a vacuum in 365.25 Earth days, without being influenced by magnetic fields.
A light year is equal to 9.46 trillion kilometers. This is exactly the distance a ray of light travels in a year. But how did astronomers achieve such precise determination of the ray path? We'll talk about this below.
How was the speed of light determined?
In ancient times, it was believed that light travels throughout the Universe instantly. However, starting in the seventeenth century, scientists began to doubt this. Galileo was the first to doubt the above proposed statement. It was he who tried to determine the time it takes for a ray of light to travel a distance of 8 km. But due to the fact that such a distance was negligibly small for such a quantity as the speed of light, the experiment ended in failure.
The first major shift in this matter was the observation of the famous Danish astronomer Olaf Roemer. In 1676, he noticed a difference in the time of eclipses depending on the approach and distance of the Earth to them in outer space. Roemer successfully connected this observation with the fact that the further the Earth moves away from, the longer it takes the light reflected from them to travel the distance to our planet.
Roemer grasped the essence of this fact accurately, but he failed to calculate the reliable value of the speed of light. His calculations were incorrect because in the seventeenth century he could not have accurate data on the distance from the Earth to other planets solar system. These data were determined a little later.
Further advances in research and the definition of the light year
In 1728, the English astronomer James Bradley, who discovered the effect of aberration in stars, was the first to calculate the approximate speed of light. He determined its value to be 301 thousand km/s. But this value was inaccurate. More advanced methods for calculating the speed of light were produced without regard to cosmic bodies - on Earth.
Observations of the speed of light in a 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.
Exact speed of light
Scientists were able 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 speed of light as 299,792.458 km/s. Astronomers still use this quantity. Further determining the daylight hours, month and year was already a matter of technology. Through simple calculations, scientists arrived at a figure of 9.46 trillion kilometers—that’s exactly how long it would take a beam of light to travel the length of the Earth’s orbit.
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 circumnavigate the entire globe (≈ 40,000 km), our racer will need 40 times more time. And this is already 4 x 40 = 160 hours. Or almost whole week 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 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 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 decided that it would be logical to measure cosmic scales in units that a radio wave (which light, in particular, is) travels over certain time intervals.
Distances.
Thus, light year- nothing more than the distance that a ray of light travels in one year. On interstellar scales, using distance units smaller than this does not make much sense. 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 with 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 closest star system to us ( 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.
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 light years to express large distances.
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 unit of distance is not used for high-precision measurements, there is no practical difference between the 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 | The Pioneer and Voyager series devices flying beyond the solar system, in about 30 years since launch, 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 | The maximum radius of the region of gravitational influence of the Sun (“Hill Spheres”) is 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. It is calculated from the age of the Universe and the maximum speed of information transmission - 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, a unit of measurement of astronomical distance equal to the distance that light travels in 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 of modern natural science. Glossary of basic terms
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