The distances between stars are so great that measuring them in kilometers or miles is an exercise with endless zeros. The usual measurement system is used to designate distances in one system. For example, they say that the minimum distance from Earth to Mars is 55.76 million kilometers. With stars, everything is more complicated, and here the concepts of light year and parsec are usually used.

Astronomical unit- a unit of measurement adopted in astronomy for objects of the Solar System and the objects of the Universe closest to it. An astronomical unit is equal to 149,598,100 km (+- ~750 km), which is approximately equal to the average distance of the Earth from the Sun. Modern observations have recorded a gradual increase in value by 15 cm annually, which is explained by the possible loss of mass by the Sun, the consequences of the solar wind.

Light year- the distance that light travels in one year, in meters it is 9,460,730,472,580,800. In fact, the light of the stars that we see on a cloudless night traveled to our planet for many centuries, and some of them no longer exist at all.

Parsec, also known as “arcsecond parallax,” is the distance from which the average radius of the Earth’s orbit (perpendicular to the line of sight) is visible at an angle of one arcsecond. Quite simply, a parsec = 3.26 light years.

It is interesting that in popular science and fantasy literature it is customary to use the concept of a light year, and parsecs are usually used only in professional works and research.

(Galaxy UDFj-39546284 is the farthest galaxy from Earth (13.3 billion light years from Earth), in the image taken by the Hubble telescope it looks like a red dot)

The closest star to us is Alpha Centauri, which is located 4.37 light years from Earth. But the most distant galaxy (as of December 2012) is as much as 13.3 billion light years from Earth! It turns out that when the sun of this very galaxy (known under the symbol UDFj-39546284) goes out, humanity will not know about it soon.

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 exactly 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

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 circumnavigate the entire globe (≈ 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 a school physics course, 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. Therefore, the 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, using distance units smaller than this does not make much sense. 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.

Textbook for 7th grade

§ 4.6. Can distance be measured in years?

Distances between stars are measured in light years. One light year is equal to the distance that light travels in empty space in a year. This is a huge distance: after all, light travels in emptiness in 1 second, almost 300,000 km.

The closest star to us (not counting the Sun) is about 4 light years away from us. But it cannot be seen with the naked eye: it is quite dim. The bright star Alpha Centauri is located relatively close to it, but it is visible mainly to residents of the Southern Hemisphere.

But almost all inhabitants of the Earth can clearly see the brightest star in the night sky - Sirius. The light from Sirius has been coming to us for almost 9 years. Sirius is much larger and brighter than our Sun: if it were at the same distance from us as the Sun, it would seem to us 20 times brighter than it. However, we would not be able to enjoy this insanely bright spectacle - all life on Earth would instantly burn out. But thanks to the fact that Sirius is far enough away from us, we can admire this brightest star as much as we want, and astronomers can study it without the danger of being “burned out by curiosity.” This study allowed them to determine the size of Sirius and even the temperature of its surface - despite the enormous distance to it!

With the help of modern powerful telescopes, astronomers study galaxies that are millions and even billions of light years away from us. Scientists see them as they were millions or billions of years ago: that's when they emitted the light that has reached us today. Therefore, by studying distant galaxies, scientists learn the distant past of our Universe, which arose about 13 billion years ago.