What is a light year? Outer space and the light year

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.

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

1. 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. Editor-in-Chief 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... ...

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

On February 22, 2017, NASA reported that 7 exoplanets were found around the single star TRAPPIST-1. Three of them are in the range of distances from the star in which the planet can have liquid water, and water is a key condition for life. It is also reported that this star system is located at a distance of 40 light years from Earth.

This message caused a lot of noise in the media; some even thought that humanity was one step away from building new settlements near a new star, but this is not so. But 40 light years is a lot, it’s a LOT, it’s too many kilometers, that is, it’s a monstrously colossal distance!

From a physics course, the third escape velocity is known - this is the speed that a body must have at the surface of the Earth in order to go beyond the solar system. The value of this speed is 16.65 km/sec. Conventional orbital spacecraft take off at a speed of 7.9 km/sec and orbit the Earth. In principle, a speed of 16-20 km/sec is quite accessible to modern earthly technologies, but no more!

Humanity has not yet learned to accelerate spaceships faster than 20 km/sec.

Let's calculate how many years it will take a starship flying at a speed of 20 km/sec to travel 40 light years and reach the star TRAPPIST-1.
One light year is the distance that a beam of light travels in a vacuum, and the speed of light is approximately 300 thousand km/sec.

A human-made spaceship flies at a speed of 20 km/sec, that is, 15,000 times slower than the speed of light. Such a ship will cover 40 light years in a time equal to 40*15000=600000 years!

An Earth ship (at the current level of technology) will reach the star TRAPPIST-1 in about 600 thousand years! Homo sapiens has existed on Earth (according to scientists) for only 35-40 thousand years, but here it is as much as 600 thousand years!

In the near future, technology will not allow humans to reach the star TRAPPIST-1. Even promising engines (ion, photon, cosmic sails, etc.), which do not exist in earthly reality, are estimated to be able to accelerate the ship to a speed of 10,000 km/sec, which means that the flight time to the TRAPPIST-1 system will be reduced to 120 years . This is already a more or less acceptable time for flight using suspended animation or for several generations of immigrants, but today all these engines are fantastic.

Even the nearest stars are still too far from people, too far, not to mention the stars of our Galaxy or other galaxies.

The diameter of our Milky Way galaxy is approximately 100 thousand light years, that is, the journey from end to end for a modern Earth ship will be 1.5 billion years! Science suggests that our Earth is 4.5 billion years old, and multicellular life is approximately 2 billion years old. The distance to the closest galaxy to us - the Andromeda Nebula - 2.5 million light years from Earth - what monstrous distances!

As you can see, of all the living people, no one will ever set foot on the earth of a planet near another star.

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 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 the light will pass beam for 365 days in 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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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 go around the whole Earth(≈ 40,000 km), our racer will need 40 times more time. And this is already 4 x 40 = 160 hours. Or almost a whole week of 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 school course physicists, 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, it is not appropriate to use distance units smaller than this special meaning. 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.

Of course, the exact meaning light years slightly different from what we calculated. But when describing distances to stars in popular science articles, the highest accuracy is, in principle, 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 Milky Way galaxy, having a diameter of approximately 100,000 light years, it will cross in 1 billion 780 million years.

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, heat 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 others. We use numbers regularly in our daily lives. And we have long been accustomed to these numbers, as if to some kind of instruments. But what happens when we get out of our everyday comfort zone and encounter something unusual for us? numerical values? In this article we will talk about the fantastic figures of the Universe.

Universal spaces

The situation with cosmic distances is even more surprising. We are fully aware of the kilometers to the neighboring city and even from Moscow to New York. But it is difficult to visualize distances 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 matter is not only in the difficulty of perceiving the huge resulting numbers, but in the number of their zeros. It becomes a problem 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 cosmic neighbors! The distance to the nearest star other than the Sun will be millions of times greater. And then, whether we measured it in kilometers or miles, astronomers would have to spend hours of their time just recording these gigantic quantities. A light year solved this problem. The solution was quite ingenious.

What is a light year equal to?

Instead of inventing a new unit of measurement that is the sum of units over small order(as happens with millimeters, centimeters, meters, kilometers), it was decided to link the distance to time. Actually, the fact that time is also a physical field influencing events is more

Moreover, interconnected and convertible with space, it was discovered by Albert Einstein and proven through his theory of relativity. The speed of light became constant. And the passage of a certain distance by a light beam per unit of time gave new physical spatial quantities: light second, light minute, light day, light month, light year. For example, per second a beam of light (in space conditions - vacuum) travels a distance of approximately 300 thousand kilometers. It is easy to calculate that one light year is equal to approximately 9.46 * 10 15. Thus, the distance from the Earth to the nearest cosmic body, the Moon, is a little more than one light second, and to the Sun is about eight light minutes. According to modern ideas, the outer bodies of the Solar System rotate in 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 launch. And these are still the celestial bodies closest to us. Light from the other end of the Milky Way takes more than a hundred thousand years to reach us.