A light year is the distance that light travels in one year. The International Astronomical Union gave its explanation of the light year - this is the distance that light travels in a vacuum, without the participation of gravity, in a Julian year. The Julian year is equal to 365 days. It is this decoding that is used in scientific literature.

If we take professional literature, then the distance is calculated in parsecs or kilo- and megaparsecs.

There are specific numbers that determine the distance of light hours, minutes, days, etc.

• A light year is equal to 9,460,800,000,000 km,
• month- 788,333 million km.,
• week- 197,083 million km.,
• day- 26,277 million km,
• hour- 1,094 million km.,
• minute- about 18 million km.,
• second- about 300 thousand km.

This is interesting! From the Earth to the Moon, light travels on average in 1.25 seconds, while its beam reaches the Sun in just over 8 minutes.

Interesting fact about the nature of the universe

The star Betelgeuse in the constellation Orion should explode in the foreseeable future (in fact, within a few centuries).

Betelgeuse is located at a distance of 495 to 640 light years from us.
If it explodes right now, then the inhabitants of the Earth will see this explosion only in 500-600 years.

And if you see an explosion today, then remember that in fact the explosion occurred around the time of Ivan the Terrible...

Earth year

An earthly year is the distance traveled by the earth in one year. If we take into account all the calculations, then one light year is equal to 63242 Earth years. This figure applies specifically to planet Earth; for others, such as Mars or Jupiter, they will be completely different. A light year measures the distance from one celestial object to another. The numbers for light years and earth years are so different, although they mean distance.

Scale

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Quick answer: not at all.

We are often asked very interesting questions, the answers to which are very non-standard. You see one of these questions in the title. And really, how many Earth years are there in one light year? You may be disappointed, but the correct answer is not at all. How so?

The thing is that a light year is not a measure of time, but a measure of distance. To be more precise, 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), according to definition of the International Astronomical Union.

Now let's try to calculate the distance of a light year. To do this, let’s take the mark of 300 thousand kilometers per second (this is the speed of light) and multiply by 31.56 million seconds (so many seconds in a year) and get a huge figure - 9,460,800,000,000 km (or 9,460,000 million kilometers). This fantastic figure means a distance that is equal to a light year.

• 1 light month ~ 788,333 million km

• 1 light week ~ 197,083 million km

• 1 light day ~ 26,277 million km

• 1 light hour ~ 1,094 million km

• 1 light minute ~ approximately 18 million km

• 1 light second ~ 300 thousand km

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 astronomy books and textbooks. 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 we 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 the other planets of the 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 developed 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.

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.

A light year is not a unit of time, as its name might lead you to believe. A light year is a unit of distance used in astronomy.

It is difficult to measure celestial distances in our usual meters and kilometers - they are so huge! A light year is the distance a ray of sunlight travels in a year, that is, in 365 days. But the speed of a light beam is almost 300 thousand kilometers per second! This means that a light year is equal to 9,460,800,000,000 km, that is, about 10 trillion kilometers. Therefore, it is much easier to say, for example: the brightest star in the sky, Sirius, is 8 light years away from us.

At first glance, this unit of measurement may seem inconvenient. But in fact, it is very convenient because of its clarity. For example, distance measured in light years indicates to which stars radio or other electromagnetic messages can be sent in order to receive a response within a real period of time, and not after hundreds or thousands of years.

Did you know that...

• The average distance to the Moon is approximately 376,300 km. This means that a beam of light sent from the surface of the Earth will take 1.2-1.3 seconds to reach the surface of our natural satellite.
• The closest star to us, other than the Sun, is Proxima Centauri, located at a distance of 4.22 light years from us.
• The diameter of our galaxy - the Milky Way - is 100,000 light years
• The closest spiral galaxy to us, the famous Andromeda Galaxy, is 2.5 million light years away from us.