Understand light years. Outer space and the light year

One way or another, in our daily lives we measure distances: to the nearest supermarket, to a relative’s house in another city, to, and so on. However, when it comes to the vastness of outer space, it turns out that using familiar values like kilometers is extremely irrational. And the point here is not only in the difficulty of perceiving the resulting gigantic values, but in the number of numbers 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 result when calculating the distance even to the nearest stars? And it is now that we need such a value as a light year. How much is it equal? Let's figure it out now.

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, larger scale units in the system

were formed quite simply: each subsequent one was a collection of units of a smaller order (centimeters, meters, kilometers, and so on). In the case of a light year, distance was tied to time. Modern science knows that the speed of light propagation in a vacuum is constant. Moreover, it is the maximum speed in nature that is permissible in modern relativistic physics. It was these ideas that formed the basis of the new meaning. A light year is equal to the distance a ray of light travels in one Earth calendar year. In kilometers it is approximately 9.46 * 10 15 kilometers. Interestingly, a photon travels the distance to the nearest Moon in 1.3 seconds. It's about eight minutes to the sun. But the next closest stars, Alpha, are already about four light years away.

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

Speed of light propagation under 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 covered by light in a year, they mean empty outer space. However, it is interesting to note that under other conditions the speed of light may be lower. For example, in air, photons scatter at a slightly lower speed than in vacuum. Which one depends on the specific state of the atmosphere. Thus, in a gas-filled environment, the light year would be somewhat smaller. However, it would not differ significantly from the accepted one.

Vast outer spaces are very difficult to calculate in kilometers or miles. Scientists are thinking about finding other units for measuring large distances. Fans of science fiction films and books often hear about the light year. But not everyone can explain what these words mean. Some do not see its difference from the ordinary earthly one.

This value is popular unit of measurement of cosmic distance. When determining it, use:

speed of light,
number of seconds equal to 365 days.

An important condition for such a calculation is the absence of influence of any gravitational fields on light. A vacuum meets this requirement. It is in it that the speed of propagation of any electromagnetic rays remains constant.

Back in the 17th century, scientists tried to determine speed of light. Previously, astronomers assumed that the rays travel through space instantly. Galileo Galilei doubted this. His goal was to calculate the time it took a beam of light to travel a certain distance, equal to eight kilometers. But his experiments were unsuccessful. The research of the Danish scientist O. Roemer was also unsuccessful. He noticed a temporary difference in the eclipses of the satellites of other planets depending on the position of the Earth. When it is further away from another space object, the light rays take longer to reach the earth's surface. He was unable to calculate their speed.

The Englishman James Bradley was the first to approximately calculate the speed of light in the 18th century. This astronomer set its value at 301,000 km/s. In the last century, using Maxwell's theory of electromagnetism, scientists were able to accurately calculate the speed of the beam. The studies were carried out using the latest laser technologies, taking into account their refractive indices. The calculated speed of light turned out to be 299,792 kilometers 458 meters per second. This helped determine a convenient unit of measurement for outer space.

What is 1 light year in kilometers?

For the calculation we took 365 days as a basis.. If you calculate the daily value in seconds, you get 86,400 seconds. And in all the indicated days their number will be 31,557,600.

We calculated how far a beam of light travels in a second. Multiplying this value by 31,557,600, we get just over 9.4 trillion. This is a light year measured in kilometers. This is the distance a light beam will travel in 365 days in a vacuum. It will travel this path, flying around the Earth’s orbit without the influence of gravitational fields.

Examples of some distances calculated this way

A ray of light travels the distance from the Earth to the Moon in 1 minute 3 seconds;
In 100,000 such years the diameter of our galactic disk can be determined;
The distance in light hours from the Sun to Pluto is 5.25 hours;
A beam from the earth will reach the Andromeda Galaxy in 2,500,000 light years, and the star Proxima Centauri in just 4;
Sunlight reaches our planet in 8.20 minutes;
The Center of our Galaxy is located at a distance of 26 thousand light years from the Sun;
The Virgo Cluster is located at a distance of 58,000 thousand similar years from our planet;
Tens of millions of such years measure galaxy clusters by diameter;
The maximum measured distance from Earth to the edge of the visible Universe was 45 billion light years.

Why is he so important?

The calculated speed of light enabled astronomers to determine distance between planets, stars, galaxies. It became obvious that the light emitted by the star does not reach the Earth with lightning speed. Observing space objects in the sky, we see the past. The explosion of a distant planet that happened hundreds of years ago will only be recorded by scientists today.

Within our Universe, the use of calculations in this unit of measurement is convenient. Less commonly used are hours, weeks or months. When determining the distance to distant space objects, the resulting value will be enormous. Using such values in mathematical calculations becomes difficult and impractical. Scientists have taken this into account, and for astronomical calculations of large distances they use another unit of measurement - the parsec. For complex mathematical calculations it is more acceptable. A light year is equal to one third of a parsec.

The ratio of light years to Earth years

In our lives we often measure distance: to work, the nearest store, another city. We compare different quantities with each other. This helps to appreciate the difference. The concepts of light years and earth years seem similar, if not the same, to many. There is a desire to compare them. Here you must first choose what is meant by an earthly year. It can be defined as the distance traveled by our planet in 365 days. With these parameters, one light period will be equal to 63 thousand Earth years.

If the earthly one is calculated in days, then it will be considered a unit of time. And light symbolizes distance. And comparison of such values is meaningless. In this case there is no answer to the question.

Video

This video will help you understand what a light year is.

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In order to understand the meaning of the concept of “light year”, you first need to remember the school physics course, especially the section that concerns the speed of light. So, the speed of light in a vacuum, where it is not affected by 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 this case, light means what is perceived by human vision.

Lesser-known units of distance are the 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 the middle of the 17th 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 have arisen 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 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 an 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.

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.
Watch	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 located approximately 26,000 light years from the Sun.
Millennium	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.
Billions of years	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.

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. Editor-in-Chief A. M. Prokhorov... ...

Physical encyclopedia LIGHT YEAR, a unit of astronomical distance equal to the distance that light travels in outer space or in a VACUUM in 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...

Big Encyclopedic Dictionary encyclopedic Dictionary - a unit of distance equal to the path traveled by light in one year. A light year is equal to 0.3 parsecs...

Exploring their own planet, over hundreds of years, people invented more and more new systems for measuring distance segments. As a result, it was decided to consider one meter as the universal unit of length, and measure the long distance in kilometers.

But the advent of the twentieth century presented humanity with a new problem. People began to carefully study space - and it turned out that the vastness of the Universe is so vast that kilometers are simply not suitable here. In conventional units you can still express the distance from the Earth to the Moon or from the Earth to Mars. But if you try to determine how many kilometers the nearest star is from our planet, the number “overgrows” with an unimaginable number of decimal places.

What is 1 light year equal to?

It became obvious that a new unit of measurement was needed to explore the spaces of space - and the light year became it. In one second, light travels 300,000 kilometers. Big Encyclopedic Dictionary - this is the distance that light will travel in exactly one year - and translated into a more familiar number system, this distance is equal to 9,460,730,472,580.8 kilometers. It is clear that using the laconic “one light year” is much more convenient than using this huge figure in calculations every time.

Of all the stars, Proxima Centauri is closest to us - it is “only” 4.22 light years away. Of course, in terms of kilometers the figure will be unimaginably huge. However, everything is learned in comparison - if you consider that the nearest galaxy called Andromeda is as much as 2.5 million light years away from the Milky Way, the above-mentioned star really begins to seem like a very close neighbor.

By the way, using light years helps scientists understand in which corners of the Universe it makes sense to look for intelligent life, and where sending radio signals is completely useless. After all, the speed of a radio signal is similar to the speed of light - accordingly, a greeting sent towards a distant galaxy will reach its destination only after millions of years. It is more reasonable to expect an answer from closer “neighbors” - objects whose hypothetical response signals will reach earthly devices at least during a person’s lifetime.

1 light year is how many Earth years?

There is a widespread misconception that the light year is a unit of time. In fact, this is not true. The term has nothing to do with earthly years, does not correlate with them in any way and refers solely to the distance that light travels in one earthly year.