500 light years in km. 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 right now 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 admissible 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.

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 books and textbooks on astronomy. 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 you 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 produced 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.

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.

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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.

As you know, to measure the distances from the Sun to the planets, as well as between the planets, scientists came up with an astronomical unit. What is it light year?

First of all, it should be noted that the light year is also a unit of measurement adopted in astronomy, but not of time (as it might seem, judging by the meaning of the word “year”), but of distance.

What is a light year equal to?

When scientists managed to calculate the distances to the nearest stars, it became obvious that the astronomical unit was inconvenient for use in the stellar world. Let's say for starters that the distance from the Sun to the nearest star is approximately 4.5 light years. This means that light from our Sun to the nearest star (by the way, it is called Proxima Centauri) takes 4.5 years to travel! How far is this distance? Let’s not bore anyone with mathematics, let’s just note that in a second, particles of light fly 300,000 kilometers. That is, if you send a signal with a flashlight towards the Moon, this light will be seen there in less than a second and a half. Light travels from the Sun to Earth in 8.5 minutes. How long then do the rays of light travel in a year?

Let's say right away: a light year is approximately 10 trillion kilometers(a trillion is one followed by twelve zeros). More precisely, 9,460,730,472,581 kilometers. If recalculated in astronomical units, it will be approximately 67,000. And this is only for the nearest star!

It is clear that in the world of stars and galaxies the astronomical unit is not suitable for measurements. It is easier to operate in calculations with light years.

Applicability in the stellar world

For example, the distance from Earth to the brightest star in the sky, Sirius, is 8 light years. And the distance from the Sun to the North Star is about 600 light years. That is, light from us gets there in 600 years. This would be approximately 40 million astronomical units. For comparison, we point out that the size (diameter) of our Galaxy - the Milky Way - is about 100,000 light years. Our closest neighbor, a spiral galaxy called the Andromeda Nebula, is 2.52 million light years away from Earth. It is very inconvenient to indicate this in astronomical units. But there are objects in the Universe that are generally 15 billion light years away from us. Thus, the radius of the observable Universe is 13.77 billion light years. And the complete Universe, as is known, extends beyond the observable part.

By the way, the diameter of the observable Universe is not at all 2 times larger than the radius, as you might think. The thing is that over time, space expands. Those distant objects that emitted light 13.77 billion years ago have flown even further away from us. Today they are more than 46.5 billion light years away. Doubling this gives us 93 billion light years. This is the true diameter of the observable Universe. So the size of the part of space that is being observed (and which is also called the Metagalaxy) is increasing all the time.

Measuring such distances in kilometers or astronomical units makes no sense. To be honest, light years don’t quite fit here either. But people have not yet come up with anything better. The numbers are so huge that only a computer can handle them.

Definition and essence of light year

Thus, light year (light year) is a unit of length, not time, which represents the distance traveled by a solar ray in a year, that is, in 365 days. This unit of measurement is very convenient for its clarity. It allows you to answer the question, after what period of time you can expect a response if you send an electromagnetic message to a certain star. And if this period is too long (for example, a thousand years), then there is no point in such actions.