Light years in kilometers. Light year in kilometers
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 nothing better people haven't figured it out yet. 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, that represents the distance traveled sunbeam per year, that is, 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.
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. In our Everyday life we use numbers regularly. 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 tie 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. The outermost bodies of the solar system modern ideas 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.
Exploring their own planet, over hundreds of years, people invented more and more new systems for measuring distance segments. As a result, it was decided to consider one meter as the universal unit of length, and measure the long distance in kilometers.
But the advent of the twentieth century confronted humanity with new problem. People began to carefully study space - and it turned out that the vastness of the Universe is so vast that kilometers are simply not suitable here. In conventional 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 equal to?
It became obvious that a new unit of measurement was needed to explore the spaces of space - and the light year became it. In one second, light travels 300,000 kilometers. Light year - this is the distance that light will travel in exactly one year - and translated into a more familiar number system, this distance is equal to 9,460,730,472,580.8 kilometers. It is clear that using the laconic “one light year” is much more convenient than using this huge figure in calculations every time.
Of all the stars, Proxima Centauri is closest to us - it is “only” 4.22 light years away. Of course, in terms of kilometers the figure will be unimaginably huge. However, everything is learned in comparison - if you consider that the nearest galaxy called Andromeda is as much as 2.5 million light years away from the Milky Way, the above-mentioned star really begins to seem like a very close neighbor.
By the way, using light years helps scientists understand in which corners of the Universe it makes sense to look for intelligent life, and where sending radio signals is completely useless. After all, the speed of a radio signal is similar to the speed of light - accordingly, a greeting sent towards a distant galaxy will reach its destination only after millions of years. It is more reasonable to expect an answer from closer “neighbors” - objects whose hypothetical response signals will reach earthly devices at least during a person’s lifetime.
1 light year is how many Earth years?
There is a widespread misconception that the light year is a unit of time. In fact, this is not true. The term has nothing to do with earthly years, does not correlate with them in any way and refers exclusively to the distance that light travels in one earthly year.
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 nova, but that's not true. 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 that 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.
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 go around the whole Earth(≈ 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 school course physicists, 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. That's why 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.
Certainly, exact value 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 from 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 one closest to us star system (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.
