Determining the distances to the nearest stars. How to measure the distance to stars? Distance to star 20

On February 22, 2017, NASA announced that 7 exoplanets have been found around the single star TRAPPIST-1. Three of them are in the range of distances from the star where 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 made a lot of noise in the media, it even seemed to some 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, this is a monstrously colossal distance!

From the course of physics, the third cosmic velocity is known - this is the velocity 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/s. Ordinary orbiting spacecraft start at a speed of 7.9 km / s, and revolve around the Earth. In principle, a speed of 16-20 km/s is quite affordable for modern earthly technologies, but no more!

Mankind has not yet learned how to accelerate spaceships faster than 20 km/sec.

Let's calculate how many years it will take for a starship flying at a speed of 20 km/s to overcome 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 300,000 km/sec.

A human-made spacecraft flies at a speed of 20 km/sec, that is, 15,000 times slower than the speed of light. Such a ship will overcome 40 light years in a time equal to 40*15000=600000 years!

An earth ship (with the current level of technology) will fly to the star TRAPPIST-1 in about 600 thousand years! Homo sapiens exists on Earth (according to scientists) only 35-40 thousand years, and here as much as 600 thousand years!

In the near future, technology will not allow a person to reach the star TRAPPIST-1. Even promising engines (ion, photon, space sails, etc.), which are not in earthly reality, can be estimated to accelerate the ship to a speed of 10,000 km / s, 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 flying with the help of suspended animation or for several generations of migrants, 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 path from end to end for a modern earthly ship will be 1.5 billion years! Science suggests that our Earth is 4.5 billion years old, and multicellular life is about 2 billion years old. The distance to the nearest galaxy to us - the Andromeda Nebula - is 2.5 million light years from Earth - what monstrous distances!

As you can see, of all people living today, no one will ever set foot on the earth of a planet near another star.

The principle of parallax on a simple example.

A method for determining the distance to stars by measuring the angle of apparent displacement (parallax).

Thomas Henderson, Vasily Yakovlevich Struve and Friedrich Bessel were the first to measure the distances to stars using the parallax method.

A diagram of the arrangement of stars within a radius of 14 light years from the Sun. Including the Sun, there are 32 known star systems in this region (Inductiveload / wikipedia.org).

The next discovery (30s of the XIX century) is the definition of stellar parallaxes. Scientists have long suspected that stars could be similar to distant suns. However, it was still a hypothesis, and, I would say, until that time it was practically not based on anything. It was important to learn how to directly measure the distance to the stars. How to do this, people understood for a long time. The Earth revolves around the Sun, and if, for example, today you make an accurate sketch of the starry sky (in the 19th century it was still impossible to take a photograph), wait half a year and re-draw the sky, you will notice that some of the stars have shifted relative to other, distant objects. The reason is simple - we are now looking at the stars from the opposite edge of the earth's orbit. There is a displacement of close objects against the background of distant ones. It is exactly the same as if we first look at the finger with one eye, and then with the other. We will notice that the finger moves against the background of distant objects (or distant objects move relative to the finger, depending on which frame of reference we choose). Tycho Brahe, the best observing astronomer of the pre-telescopic era, tried to measure these parallaxes but did not find them. In fact, he simply gave a lower limit on the distance to stars. He said that the stars were at least more than a light-month away (although such a term, of course, could not yet exist). And in the 1930s, the development of telescopic observation technology made it possible to more accurately measure the distances to stars. And it is not surprising that three people at once in different parts of the globe made such observations for three different stars.

Thomas Henderson was the first to formally correctly measure the distance to the stars. He observed Alpha Centauri in the Southern Hemisphere. He was lucky, he almost accidentally chose the closest star from those that are visible to the naked eye in the southern hemisphere. But Henderson believed that he lacked the accuracy of observations, although he received the correct value. The mistakes, in his opinion, were large, and he did not immediately publish his result. Vasily Yakovlevich Struve observed in Europe and chose the bright star of the northern sky - Vega. He was also lucky - he could have chosen, for example, Arcturus, which is much further. Struve determined the distance to Vega and even published the result (which, as it turned out later, was very close to the truth). However, he specified and changed it several times, and therefore many felt that this result could not be trusted, since the author himself constantly changes it. But Friedrich Bessel acted differently. He chose not a bright star, but one that moves quickly across the sky - 61 Cygnus (the name itself says that it is probably not very bright). The stars move slightly relative to each other, and, of course, the closer the stars are to us, the more noticeable this effect. In the same way that roadside poles flicker very quickly outside the window on a train, the forest only slowly shifts, and the Sun actually stands still. In 1838 he published a very reliable parallax of the star 61 Cygni and correctly measured the distance. These measurements proved for the first time that the stars are distant suns, and it became clear that the luminosity of all these objects corresponded to the solar value. Determination of parallaxes for the first tens of stars made it possible to construct a three-dimensional map of solar neighborhoods. Still, it has always been very important for a person to build maps. It made the world seem a little more controlled. Here is a map, and already a foreign area does not seem so mysterious, probably dragons do not live there, but just some kind of dark forest. The advent of measuring the distances to stars really made the nearest solar neighborhood of a few light years somehow more, perhaps, friendly.

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The material of the issue was kindly provided by Sergey Borisovich Popov - astrophysicist, Doctor of Physical and Mathematical Sciences, Professor of the Russian Academy of Sciences, Leading Researcher of the State Astronomical Institute. Sternberg of Moscow State University, winner of several prestigious awards in the field of science and education. We hope that familiarity with the issue will be useful for both schoolchildren, parents, and teachers - especially now that astronomy has again entered the list of compulsory school subjects (Order No. 506 of the Ministry of Education and Science of June 7, 2017).

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Proxima Centauri.

Here's a classic backfill question. Ask your friends Which one is closest to us?" and then watch them list nearest stars. Maybe Sirius? Alpha something there? Betelgeuse? The answer is obvious - it is; a massive ball of plasma located about 150 million kilometers from Earth. Let's clarify the question. Which star is closest to the Sun?

nearest star

You have probably heard that - the third brightest star in the sky at a distance of only 4.37 light years from. But Alpha Centauri not a single star, it is a system of three stars. First, a binary star (binary star) with a common center of gravity and an orbital period of 80 years. Alpha Centauri A is only slightly more massive and brighter than the Sun, while Alpha Centauri B is slightly less massive than the Sun. There is also a third component in this system, a dim red dwarf Proxima Centauri (Proxima Centauri).

Proxima Centauri- That's what it is closest star to our sun, located at a distance of only 4.24 light years.

Proxima Centauri.

Multiple star system Alpha Centauri located in the constellation Centaurus, which is only visible in the southern hemisphere. Unfortunately, even if you see this system, you will not be able to see Proxima Centauri. This star is so dim that you need a powerful enough telescope to see it.

Let's find out the scale of how far Proxima Centauri from U.S. Think about. moves at a speed of almost 60,000 km / h, the fastest in. He overcame this path in 2015 for 9 years. Traveling so fast to get to Proxima Centauri, New Horizons will need 78,000 light years.

Proxima Centauri is the nearest star over 32,000 light years, and it will hold this record for another 33,000 years. It will make its closest approach to the Sun in about 26,700 years, when the distance from this star to the Earth will be only 3.11 light years. In 33,000 years, the nearest star will be Ross 248.

What about the northern hemisphere?

For those of us who live in the northern hemisphere, the nearest visible star is Barnard's Star, another red dwarf in the constellation Ophiuchus (Ophiuchus). Unfortunately, like Proxima Centauri, Barnard's Star is too dim to see with the naked eye.

Barnard's Star.

nearest star, which you can see with the naked eye in the northern hemisphere is Sirius (Alpha Canis Major). Sirius is twice the size and mass of the Sun and is the brightest star in the sky. Located 8.6 light-years away in the constellation Canis Major (Canis Major), it is the most famous star chasing Orion in the night sky during the winter.

How did astronomers measure the distance to stars?

They use a method called . Let's do a little experiment. Hold one arm outstretched at length and place your finger so that some distant object is nearby. Now alternately open and close each eye. Notice how your finger seems to jump back and forth when you look with different eyes. This is the parallax method.

Parallax.

To measure the distance to the stars, you can measure the angle to the star with respect to when the Earth is on one side of the orbit, say in the summer, then 6 months later when the Earth moves to the opposite side of the orbit, and then measure the angle to the star compared to which some distant object. If the star is close to us, this angle can be measured and the distance calculated.

You can really measure the distance in this way to nearby stars, but this method only works up to 100,000 light years.

20 nearest stars

Here is a list of the 20 nearest star systems and their distances in light years. Some of them have several stars, but they are part of the same system.

According to NASA, there are 45 stars within a radius of 17 light years from the Sun. There are over 200 billion stars in the universe. Some of them are so dim that they are almost impossible to detect. Perhaps with new technologies, scientists will find stars even closer to us.

The title of the article you read "Closest Star to the Sun".

Surely, having heard in some fantastic action movie the expression a la “20 to Tatooine light years”, many asked legitimate questions. I will name some of them:

Isn't a year a time?

Then what is light year?

How many kilometers does it have?

How long will it take light year space ship with Earth?

I decided to dedicate today's article to explaining the meaning of this unit of measurement, comparing it with our usual kilometers and demonstrating the scales that Universe.

Virtual Racer.

Imagine a person, in violation of all the rules, rushing along the highway at a speed of 250 km / h. In two hours he will overcome 500 km, and in four - as many as 1000. Unless, of course, he crashes in the process ...

It would seem that this is the speed! But in order to circumnavigate the entire globe (≈ 40,000 km), our rider 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. Since 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 the globe, thus, it will go around in 0.134 seconds. That's 4,298,507 times faster than our virtual racer!

From Earth before Moon light reaches on average in 1.25 s, up to sun its beam will rush 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 passes over certain time intervals (which light, in particular, is).

Distances.

In this way, light year- nothing more than the distance that a ray of light overcomes in one year. On interstellar scales, using distance units smaller than this does not make much sense. And yet they are. 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.

And 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. Light travels 300,000 km in one second. Consequently, 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 SIXTY BILLION AND EIGHT HUNDRED MILLION kilometers.

Of course, the exact value light year 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...

Scales.

Let's assume modern spaceship leaves solar system with the third space velocity (≈ 16.7 km/s). The first light year he will overcome in 18,000 years!

4,36 light years to our nearest star system ( Alpha Centauri, see the image at the beginning) it will overcome in about 78 thousand years!

Our the Milky Way galaxy, having a diameter of approximately 100,000 light years, it will cross in 1 billion 780 million years.

And to the nearest one to us galaxies, spaceship rushing only after 36 billion years ...

These are the pies. But in theory, even Universe arose only 16 billion years ago ...

And finally...

You can start to wonder at the cosmic scale even without going beyond solar system because it is very large in itself. This was shown very well and clearly, for example, by the creators of the project If the Moon wereonly 1 pixel (If the moon were just one pixel): http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html .

On this I, perhaps, will complete today's article. All your questions, comments and wishes are welcome in the comments below it.

Due to the annual movement of the Earth in its orbit, nearby stars move slightly relative to distant "fixed" stars. For a year, such a star describes a small ellipse on the celestial sphere, the dimensions of which are the smaller, the farther the star is. In angular measure, the major semiaxis of this ellipse is approximately equal to the maximum angle at which 1 AU is visible from the star. e. (major axis of the earth's orbit), perpendicular to the direction of the star. This angle (), called the annual or trigonometric parallax of a star, equal to half of its apparent displacement per year, serves to measure the distance to it on the basis of trigonometric relationships between the sides and angles of the ESA triangle, in which the angle and basis are known - the semi-major axis of the earth's orbit (see Fig. 1).

Figure 1. Determining the distance to a star using the parallax method (A - star, Z - Earth, C - Sun).

Distance r to the star, determined by the value of its trigonometric parallax, is equal to:

r = 206265""/ (a.u.),

where parallax is expressed in arcseconds.

For the convenience of determining the distances to stars using parallaxes, astronomy uses a special unit of length - the parsec (ps). A star at a distance of 1 ps has a parallax of 1"". According to the above formula, 1 ps \u003d 206265 a. e. = 3.086 10 18 cm.

Along with the parsec, another special unit of distance is used - a light year (i.e., the distance that light travels in 1 year), it is equal to 0.307 ps, or 9.46 10 17 cm.

The star closest to the solar system - a red dwarf of the 12th magnitude Proxima Centauri - has a parallax of 0.762, i.e., the distance to it is 1.31 ps (4.3 light years).

The lower limit for measuring trigonometric parallaxes is ~0.01"", so they can be used to measure distances not exceeding 100 ps with a relative error of 50%. (For distances up to 20 ps, ​​the relative error does not exceed 10%.) This method has so far determined the distances of up to about 6000 stars. Distances to more distant stars in astronomy are determined mainly by the photometric method.

Table 1. Twenty nearest stars.