1 light year is equal to earth years. Light year and cosmic scales
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. Römer 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 irrespective 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.
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 expanse 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.
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1 kilometer [km] = 1.0570008340247E-13 light year [St. G.]
Initial value
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meter exameter petameter terameter gigameter megameter kilometer hectometer decameter decimeter centimeter millimeter micrometer micron nanometer picometer femtometer attometer megaparsec kiloparsec parsec light year astronomical unit (international) mile (statute) mile (US, geodetic) mile (Roman) 1000 yards furlong furlong (US, geodetic) chain chain (US, geodetic) rope (English rope) genus genus (US, geodetic) perch field (eng. pole) fathom fathom (US, geodetic) cubit yard foot foot (US, geodetic) link link (US, geodetic) cubit (Brit.) hand span finger nail inch inch (US, geodetic) barleycorn (eng. barleycorn) thousandth of a microinch angstrom atomic unit of length x-unit fermi arpan soldering typographic point twip cubit (Swedish) fathom (Swedish) caliber centiinch ken arshin actus (O.R.) vara de tarea vara conu quera vara castellana cubit (Greek) long reed reed long cubit palm "finger" Planck length classical electron radius Bohr radius equatorial radius of the Earth polar radius of the Earth distance from the Earth to the Sun radius of the Sun light nanosecond light microsecond light millisecond light second light hour light days light week Billion light-years Distance from the Earth to the Moon cable lengths (international) cable lengths (British) cable lengths (USA) nautical mile (USA) light minute rack unit horizontal pitch cicero pixel line inch (Russian) vershok span foot fathom oblique fathom verst boundary verst
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More about length and distance
General information
Length is the largest measurement of the body. In three dimensions, length is usually measured horizontally.
Distance is a measure of how far two bodies are from each other.
Distance and length measurement
Distance and length units
In the SI system, length is measured in meters. Derived quantities such as kilometer (1000 meters) and centimeter (1/100 meter) are also widely used in the metric system. In countries that do not use the metric system, such as the US and the UK, units such as inches, feet, and miles are used.
Distance in physics and biology
In biology and physics, lengths are often measured much less than one millimeter. For this, a special value, a micrometer, has been adopted. One micrometer is equal to 1×10⁻⁶ meters. In biology, micrometers measure the size of microorganisms and cells, and in physics, the length of infrared electromagnetic radiation. A micrometer is also called a micron and sometimes, especially in English literature, is denoted by the Greek letter µ. Other derivatives of the meter are also widely used: nanometers (1×10⁻⁹ meters), picometers (1×10⁻¹² meters), femtometers (1×10⁻¹⁵ meters), and attometers (1×10⁻¹⁸ meters).
Distance in navigation
Shipping uses nautical miles. One nautical mile is equal to 1852 meters. Initially, it was measured as an arc of one minute along the meridian, that is, 1/(60 × 180) of the meridian. This made latitude calculations easier, since 60 nautical miles equaled one degree of latitude. When distance is measured in nautical miles, speed is often measured in nautical knots. One knot is equal to one nautical mile per hour.
distance in astronomy
In astronomy, long distances are measured, so special quantities are adopted to facilitate calculations.
astronomical unit(au, au) is equal to 149,597,870,700 meters. The value of one astronomical unit is a constant, that is, a constant value. It is generally accepted that the Earth is located at a distance of one astronomical unit from the Sun.
Light year equals 10,000,000,000,000 or 10¹³ kilometers. This is the distance that light travels in a vacuum in one Julian year. This value is used in popular science literature more often than in physics and astronomy.
Parsec approximately equal to 30,856,775,814,671,900 meters or approximately 3.09 × 10¹³ kilometers. One parsec is the distance from the Sun to another astronomical object, such as a planet, star, moon, or asteroid, with an angle of one arc second. One arc second is 1/3600 of a degree, or about 4.8481368 mrad in radians. Parsec can be calculated using parallax - the effect of a visible change in the position of the body, depending on the point of observation. During measurements, a segment E1A2 (in the illustration) is laid from the Earth (point E1) to a star or other astronomical object (point A2). Six months later, when the Sun is on the other side of the Earth, a new segment E2A1 is drawn from the new position of the Earth (point E2) to the new position in space of the same astronomical object (point A1). In this case, the Sun will be at the intersection of these two segments, at point S. The length of each of the segments E1S and E2S is equal to one astronomical unit. If we postpone the segment through the point S, perpendicular to E1E2, it will pass through the intersection point of the segments E1A2 and E2A1, I. The distance from the Sun to point I is the SI segment, it is equal to one parsec when the angle between the segments A1I and A2I is two arcseconds.
On the image:
- A1, A2: apparent star position
- E1, E2: Earth position
- S: position of the sun
- I: point of intersection
- IS = 1 parsec
- ∠P or ∠XIA2: parallax angle
- ∠P = 1 arc second
Other units
league- an obsolete unit of length used earlier in many countries. It is still used in some places, such as the Yucatan Peninsula and rural areas of Mexico. This is the distance a person walks in an hour. Marine League - three nautical miles, approximately 5.6 kilometers. Lie - a unit approximately equal to the league. In English, both leagues and leagues are called the same, league. In literature, the league is sometimes found in the title of books, such as "20,000 Leagues Under the Sea" - the famous novel by Jules Verne.
Elbow- an old value equal to the distance from the tip of the middle finger to the elbow. This value was widespread in the ancient world, in the Middle Ages, and until modern times.
Yard used in the British imperial system and is equal to three feet or 0.9144 meters. In some countries, such as Canada, where the metric system is adopted, yards are used to measure the fabric and length of swimming pools and sports fields and grounds, such as golf and football courses.
Meter Definition
The definition of the meter has changed several times. The meter was originally defined as 1/10,000,000 of the distance from the North Pole to the equator. Later, the meter was equal to the length of the platinum-iridium standard. Later, the meter was equated to the wavelength of the orange line of the electromagnetic spectrum of the krypton atom ⁸⁶Kr in vacuum, multiplied by 1,650,763.73. Today, a meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
Computing
In geometry, the distance between two points, A and B, with coordinates A(x₁, y₁) and B(x₂, y₂) is calculated by the formula:
and within a few minutes you will receive an answer.Calculations for converting units in the converter " Length and distance converter' are performed using the functions of unitconversion.org .
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.
| Scale | Value (St. Years) | Description |
|---|---|---|
| Seconds | 4 10 −8 | The average distance to is approximately 380,000 km. This means that it takes about 1.3 seconds for a beam of light emitted from the surface 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 Earth in about 500 seconds (8 minutes 20 seconds). |
| Clock | 0,0006 | The average distance from the Sun to approximately 5 light hours. |
| 0,0016 | Apparatuses of the Pioneer and series, flying beyond, approximately 30 years after the launch, retired 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 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 | The maximum radius of the region of the gravitational influence of the Sun ("Hill's Spheres") is approximately 125,000 AU. e. | |
| 4,2 | The closest to us (not counting the Sun), Proxima Centauri, is located at a distance of 4.2 sv. of the year. | |
| Millennium | 26 000 | The center of our Galaxy is approximately 26,000 light-years from the Sun. |
| 100 000 | Our disk diameter 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 nearest one, the Virgo cluster, is 58 million light-years away from us. | |
| Tens of millions of light years | The characteristic size of clusters of galaxies in diameter. | |
| 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 world, 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. It is calculated from the age of the Universe and the maximum information transfer rate - 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). |
Whatever lifestyle we lead, whatever we do, one way or another, we use some units of measurement every day. We ask for a glass of water, warm up our own breakfast to a certain temperature, visually estimate how far we need to walk to the nearest post office, arrange a meeting at a certain time, and so on. All these actions require
Not just calculations, but also a certain measurement of various numerical categories: distance, quantity, weight, time, and so on. We use numbers regularly in our daily life. And these numbers have long been accustomed to, as if to some kind of tools. But what happens when we get out of our everyday comfort zone and encounter numbers that are unusual for us? In this article we will talk about the fantastic figures of the Universe.
universal open spaces
Even more surprising is the situation with cosmic distances. We are quite aware of the kilometers to the neighboring city and even from Moscow to New York. But it's hard to imagine distances visually when it comes to the scale of star clusters. It is now that we will need the so-called light year. After all, the distances even between neighboring stars are extremely large, and measuring them in kilometers or miles is simply irrational. And here the point is not only in the difficulty of perceiving the huge resulting numbers, but in the number of their zeros. The problem becomes to write the number. For example, the distance from Earth to Mars during the period of closest approach is 55.7 million kilometers. A value with six zeros. But Mars is one of our closest space neighbors! The distance to the nearest star, except for the Sun, will be millions of times greater. And then, if we measured it in kilometers or miles, astronomers would have to spend hours of their time just recording these gigantic quantities. The light year solved this problem. The way out was quite ingenious.
What is a light year?
Instead of inventing a new unit of measurement, which is the sum of units of a smaller order (as happens with millimeters, centimeters, meters, kilometers), it was decided to tie distance to time. Actually, the fact that time is also a physical field that affects events is more
moreover, interconnected and convertible with space, was discovered by Albert Einstein and proved through his theory of relativity. The speed of light has become a constant speed. And the passage of a light beam of a certain distance per unit of time gave new physical spatial quantities: a light second, a light minute, a light day, a light month, a light year. For example, in a second a beam of light (in space conditions - vacuum) travels a distance of about 300 thousand kilometers. It is easy to calculate that one light year is equal to approximately 9.46 * 10 15 . So, the distance from the Earth to the nearest cosmic body, the Moon, is a little more than one light second, to the Sun - about eight light minutes. The outlying bodies of the solar system, according to modern concepts, orbit at a distance of one light year. The next closest star to us, or rather, a system of double stars, Alpha and Proxima Centauri, is so far away that even the light from them reaches our telescopes only four years after its start. And after all, these are still the celestial bodies closest to us. Light from the other end of the Milky Way takes over a hundred thousand years to reach us.