Distance 4 light years. How is distance to stars measured and what is a light year? Light year and other distances

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 for distances in outer space. It is commonly used in popular astronomy books and textbooks. Nevertheless, in professional astrophysics, this figure is used extremely rarely and often to determine the 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 textbook of astronomy. A light year is the distance that a ray of light travels in one Earth year. Such a definition may satisfy an amateur, but a cosmologist will consider 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 ray of light travels in a vacuum in 365.25 Earth days without being influenced 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 the speed of light was determined

In ancient times, it was believed that light spreads in the universe instantly. However, beginning in the seventeenth century, scholars began to doubt this. Galileo was the first to question the above statement. It was he who tried to determine the time it takes for a beam of light to travel 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 matter was the observation of the famous Danish astronomer Olaf Roemer. In 1676, he noticed a difference in the time of an eclipse 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 for light reflected from them to travel the distance to our planet.

Roemer grasped the essence of this fact exactly, but he did not succeed in calculating the reliable value of the speed of light. His calculations were incorrect, since 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 light year definition

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 at 301 thousand km / s. But this value was imprecise. More sophisticated methods of calculating the speed of light were made 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. Fisot and L. Foucault, respectively. With their help, physicists managed to get closer to the real value of this value.

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, with the help of modern laser technology and calculations corrected for the refractive index of the ray flux in the 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, it was already a matter of technology to determine the daylight hours, month and year. Through simple calculations, scientists have obtained a figure of 9.46 trillion kilometers - that is how long it would take for a ray of light to fly around the length of the earth's orbit.

Surely, having heard in some fantastic action movie an expression a la “to Tatooine twenty light years”, Many asked legitimate questions. I will voice some of them:

Isn't the year the time?

Then what is it light year?

How many kilometers are there?

How much will it take 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 scales with which it operates Universe.

Virtual racer.

Imagine a person, in violation of all the rules, rushing along the highway at a speed of 250 km / h. In two hours he will overcome 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 rider will need 40 times longer. And this is already 4 x 40 \u003d 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. Since laziness has always forced us to come up with and use shorter alternative units of measurement.

Limit.

From the school physics course, everyone should know that the fastest rider in The universe - light. In one second, its beam covers a distance of about 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 light reaches an average of 1.25 s, to Suns its beam will fly in a little over 8 minutes.

Colossal, isn't it? But the existence of speeds higher than the speed of light has not yet been proven. Therefore, the scientific world decided that it would be logical to measure cosmic scales in units that a radio wave passes over certain time intervals (which light, in particular, is).

Distances.

Thus, light year - nothing more than the distance that a ray of light travels in one year. On an interstellar scale, using distance units smaller than this does not make much sense. And yet they are. 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.

And now, so that you understand where the numbers come from, let's calculate what one is 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 \u003d 31,536,000 seconds. In one second, light travels 300,000 km. Consequently, in a year its ray will cover the distance of 31,536,000 x 300,000 \u003d 9,460,800,000,000 km.

This number is read like this: NINE TRILLION, FOUR SIXTY BILLION AND EIGHT HUNDRED MILLION kilometers.

Of course the exact meaning light year slightly different from what we calculated. But when describing the distances to stars in popular science articles, the highest accuracy is basically not needed, and a hundred or two million kilometers will not play a special role here.

Now let's continue our thought experiments ...

The scale.

Suppose modern spaceship leaves Solar system with the third cosmic speed (≈ 16.7 km / s). The first light year it will overcome in 18,000 years!

4,36 light years to the closest star system ( Alpha Centauri, see image at the beginning) it will overcome in about 78 thousand years!

Our the milky way galaxywith a diameter of about 100,000 light years, it will cross in 1 billion 780 million years.

A non-systemic unit of length used in astronomy; 1 S. g is equal to the distance traveled by light in 1 year. 1 S. year \u003d 0.3068 parsec \u003d 9.4605 1015 m. Physical encyclopedic dictionary. M .: Soviet encyclopedia. Chief Editor A.M. Prokhorov. ... ... Physical encyclopedia

LIGHT YEAR, a unit of astronomical distance equal to the distance that light travels in open space or in 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. Distance to the closest star (Proxima Centaur) is approximately 4.3 light years. The most distant stars of the Galaxy are located on ... ... Modern encyclopedia

A unit of interstellar distance; the path that light travels in a year, that is, 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. Km 9,466´1012. Distance to the closest star (Proxima Centaur) is approximately 4.3 light years. The most distant stars of the Galaxy are located on ... ... Illustrated Encyclopedic Dictionary

A non-systemic unit of length used in astronomy. 1 light year is the distance that light travels in 1 year. 1 light year equals 9.4605E + 12 km \u003d 0.307 pc ... Astronomical Dictionary

The 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, that is, 9.46X1012 km ... encyclopedic Dictionary

Light year is a unit of distance equal to the path traveled by light in one year. A light year is 0.3 parsec ... Concepts of modern natural science. Glossary of basic terms

light year - šviesmetis statusas T sritis Standartizacija ir metrologija apibrėžtis Astronominis ilgio matavimo vienetas, lygus nuotoliui, kurį vakuume nusklinda šviesa per 1 atogrąžinius metus. Žymimas šm: 1 šm \u003d 9.46073 · 10¹² km. atitikmenys: angl. light…… Penkiakalbis aiškinamasis metrologijos terminų žodynas

light year - šviesmetis statusas T sritis fizika atitikmenys: angl. light year vok. Lichtjahr, n rus. light year, m pranc. année lumière, f ... Fizikos terminų žodynas

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

But the onset of the twentieth century posed a new problem for humanity. People began to carefully study space - and it turned out that the vastness of the Universe is so immense that kilometers are simply not suitable here. In the usual 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?

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

Of all the stars, Proxima Centauri is the closest to us - it is removed "only" by 4.22 light years. Of course, in terms of kilometers, the figure will turn out to be unimaginably huge. However, everything is learned by comparison - if you consider that the nearest galaxy called Andromeda is at a distance of 2.5 million light years from the Milky Way, the aforementioned star really begins to seem like a very close neighbor.

By the way, the use of light years helps scientists understand in which parts of the Universe it makes sense to look for intelligent life, and where it is completely useless to send radio signals. After all, the speed of the radio signal is similar to the speed of light - accordingly, a greeting sent to the direction of a distant galaxy will reach its goal only after millions of years. It is more reasonable to expect an answer from closer "neighbors" - objects, the hypothetical response signals of which will reach the terrestrial vehicles at least during a person's life.

How many Earth years is 1 light year?

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

Galactic distance scales

Light year ( st. g., ly) is a non-systemic unit of length equal to the distance traveled by light in one year.

More precisely, according to the definition of the International Astronomical Union (IAS), a light year is equal to the distance that light travels in a vacuum, without experiencing the influence of 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 the professional literature, parsecs and multiples (kilo- and megaparsecs) are usually used to express long distances instead of light years.

Previously (until 1984) a light year was the distance traveled by light in one tropical year, attributed to the epoch 1900.0. The new definition differs from the old 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.

Numerical values

A light year is:

• 9 460 730 472 580 800 meters (approximately 9.46 petameters)
• 63,241,077 Astronomical Units (AU)
• 0.306 601 parsecs

Related units

The following units are used quite rarely, usually only in popular publications:

• 1 light second \u003d 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

A light year is good for representing distance scales in astronomy.