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 step out of our everyday comfort zone and encounter numerical values ​​that are unusual for us? 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, which is the sum of units of a smaller order (as happens with millimeters, centimeters, meters, kilometers), it was decided to link 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 concepts, 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.

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 it is now that 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.

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 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.

For their calculations, astronomers use special units of measurement that are not always clear to ordinary people. This is understandable, because if cosmic distances were measured in kilometers, then the number of zeros would dazzle your eyes. Therefore, to measure cosmic distances it is customary to use much larger quantities: astronomical unit, light year and parsec.

Quite often used to indicate distances within our native Solar System. If we can also express it in kilometers (384,000 km), then the closest path to Pluto is approximately 4,250 million km, and this will be difficult to understand. For such distances, it is time to use an astronomical unit (AU), equal to the average distance from the earth's surface to the Sun. In other words, 1 a.u. corresponds to the length of the semimajor axis of our Earth’s orbit (150 million km). Now, if you write that the shortest distance to Pluto is 28 AU, and the longest path can be 50 AU, it is much easier to imagine.

The next largest is a light year. Although the word “year” is present there, one should not think that we are talking about time. One light year is 63,240 AU. This is the path that a ray of light travels over the course of 1 year. Astronomers have calculated that from the most distant corners of the Universe, a ray of light takes more than 10 billion years to reach us. To imagine this gigantic distance, let's write it in kilometers: 95000000000000000000000. Ninety-five billion trillion usual kilometers.

Scientists began to guess that light does not travel instantly, but at a certain speed, starting in 1676. It was at this time that a Danish astronomer named Ole Roemer noticed that the eclipses of one of Jupiter's satellites were beginning to lag, and this was happening precisely when the Earth was heading in its orbit to the opposite side of the Sun, the opposite side of where Jupiter was. Some time passed, the Earth began to move back, and eclipses again began to approach their previous schedule.

Thus, about 17 minutes of time difference were noted. From this observation it was concluded that it took light 17 minutes to travel a distance the length of the Earth's orbit. Since the diameter of the orbit was proven to be approximately 186 million miles (now this constant is 939,120,000 km), it turned out that the light beam moves at a speed of about 186 thousand miles per second.

Already in our time, thanks to Professor Albert Michelson, who set out to determine as accurately as possible what a light year is, using a different method the final result was obtained: 186,284 miles in 1 second (approximately 300 km/s). Now, if we count the number of seconds in a year and multiply by this number, we find that a light year is 5,880,000,000,000 miles long, which corresponds to 9,460,730,472,580.8 km.

For practical purposes, astronomers often use a unit of distance called the parsec. It is equal to the displacement of the star against the background of other celestial bodies by 1"" when the observer is displaced by 1 radius

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 accepted 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 one and a half seconds. 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.