What is a light year and what is it equal to? What is a light year equal to? The star is 20 light years away.
Astronomers have discovered the first potentially habitable planet outside the solar system.
The reason for this conclusion is provided by the work of American “exoplanet hunters” (exoplanets are those that revolve around other stars, and not around the Sun).
It is published by the Astrophysical Journal. The publication can be found on the website arXiv.org.
The red dwarf Gliese-581, which, when viewed from Earth, is located in the constellation Libra at a distance of 20.5 light years (one light year = the distance that light travels in a year at a speed of 300 thousand km/sec.), has long attracted attract the attention of “exoplanet hunters”.
It is known that among the exoplanets discovered so far, most are very massive and similar to Jupiter - they are easier to find.
In April last year, a planet was found in the Gliese-581 system, which at that time became the lightest known solar planets outside the Solar System, orbiting stars similar in parameters to the Sun.
Planet Gliese-581e (the fourth in that system) turned out to be only 1.9 times more massive than Earth.
This planet orbits its star in just 3 (Earth) days and 4 hours.
Now scientists are reporting the discovery of two more planets in this star system. Of greatest interest is the sixth planet discovered - Gliese-581g.
It is what astronomers call the first suitable for life.
Using our own and archival data from the Keck telescope, which is based on Hawaiian Islands, researchers measured the parameters of this planet and came to the conclusion that there may be an atmosphere and liquid water there.
Thus, scientists have established that this planet has a radius from 1.2 to 1.5 Earth radii, a mass from 3.1 to 4.3 Earth masses and a period of revolution around its star of 36.6 Earth days. The semimajor axis of this planet's elliptical orbit is about 0.146 astronomical units (1 astronomical unit is the average distance between the Earth and the Sun, which is approximately 146.9 million km).
The acceleration of free fall on the surface of this planet exceeds a similar parameter for the Earth by 1.1-1.7 times.
As for the temperature regime on the surface of Gliese-581g, it, according to scientists, ranges from -31 to -12 degrees Celsius.
And although for the average person this range cannot be called anything other than frosty, on Earth life exists in a much wider range from -70 in Antarctica to 113 degrees Celsius in geothermal springs where microorganisms live.
Since the planet is quite close to its star, there is a high probability that Gliese-581g, due to tidal forces, is always turned to one side towards its star, just as the Moon always “looks” at the Earth with only one of its hemispheres.
The fact that in less than 20 years, astronomers have gone from discovering the first planet around other stars to potentially habitable planets, indicates, according to the authors of the sensational work, that there are many more such planets than previously thought.
And even our galaxy Milky Way, perhaps, replete with potentially habitable planets.
To discover this planet, it took more than 200 measurements with an accuracy of, for example, a speed of 1.6 m/sec.
Since our galaxy is home to hundreds of billions of stars, scientists conclude that tens of billions of them have potentially habitable planets.
Category: Tags:The principle of parallax using 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 distances to stars using the parallax method.
Diagram of the location 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 19th century) is the determination of stellar parallaxes. Scientists have long suspected that stars might be similar to distant suns. However, it was still a hypothesis, and, I would say, until that time it was based on practically nothing. It was important to learn how to directly measure the distance to the stars. People have understood how to do this for a long time. The Earth revolves around the Sun, and if, for example, today we make an accurate sketch starry sky(in the 19th century it was still impossible to take a photograph), wait six months and re-sketch 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. This is exactly the same as if we first look at a finger with one eye and then with the other. We will notice that the finger is displaced against the background of distant objects (or distant objects are displaced relative to the finger, depending on which frame of reference we choose). Tycho Brahe, the best observational astronomer of the pre-telescoping era, tried to measure these parallaxes but did not detect them. In fact, he simply gave a lower limit on the distance to the stars. He said that the stars are at least further away than about a light month (although such a term, of course, could not yet exist). And in the 30s, the development of telescopic observation technology made it possible to more accurately measure distances to stars. And it is not surprising that three people at once different parts 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 most a nearby star from those that are visible naked eye in the Southern Hemisphere. But Henderson believed that he lacked the accuracy of his observations, although he got the correct value. The mistakes, in his opinion, were big, and he did not immediately publish his results. Vasily Yakovlevich Struve observed in Europe and chose a bright star northern sky- Vega. He was also lucky - he could have chosen, for example, Arcturus, which is much further away. 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 clarified it several times, changed it, and therefore many felt that this result could not be trusted, since the author himself was constantly changing it. But Friedrich Bessel acted differently. He chose not a bright star, but one that moves quickly across the sky - 61 Cygni (the name itself says that it is probably not very bright). The stars move a little relative to each other, and, naturally, the closer the stars are to us, the more noticeable this effect is. Just as on a train, roadside pillars flash very quickly outside the window, the forest only slowly moves, 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 were distant suns, and it became clear that the luminosity of all these objects corresponded to the solar value. Determining the parallaxes for the first tens of stars made it possible to construct a three-dimensional map of the solar neighborhood. After all, 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 the foreign area no longer seems so mysterious, probably dragons don’t live there, but just some kind of dark forest. The advent of measuring distances to stars has indeed made the nearest solar neighborhood, several light years away, somewhat more, well, friendly.
The release material was kindly provided by Sergei Borisovich Popov - astrophysicist, Doctor of Physical and Mathematical Sciences, Professor Russian Academy Sciences, leading researcher at the State Astronomical Institute named after. Sternberg of Moscow state university, winner of several prestigious awards in the field of science and education. We hope that getting acquainted with the issue will be useful for schoolchildren, parents, and teachers - especially now that astronomy is again included in the list of compulsory school subjects (order No. 506 of the Ministry of Education and Science of June 7, 2017).
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Cosmic distances are difficult to measure in ordinary meters and kilometers, so astronomers use other physical units. One of them is called a light year.
Many fantasy fans are very familiar with this concept, as it often appears in films and books. But not everyone knows what a light year is, and some even think that it is similar to the usual annual calculation of time.
What is a light year?
In reality, a light year is not a unit of time, as one might assume, but a unit of length used in astronomy. It refers to the distance traveled by light in one year.
It is usually used in astronomy textbooks or popular science fiction to determine lengths within the solar system. For more accurate mathematical calculations or measuring distances in the Universe, another unit is taken as a basis - .
Appearance light years in astronomy was associated with the development of stellar sciences and the need to use parameters comparable to the scale of space. The concept was introduced several years after the first successful measurement of the distance from the Sun to the star 61 Cygni in 1838. 
Initially, a light year was the distance traveled by light in one tropical year, that is, in a period of time equal to the full cycle of seasons. However, since 1984, the Julian year (365.25 days) began to be used as a basis, as a result of which the measurements became more accurate.
How is the speed of light determined?
To calculate a light year, researchers had to first determine the speed of light. Astronomers once believed that the propagation of rays in space was instantaneous, but in the 17th century this conclusion began to be questioned.
The first attempts to make calculations were made by Galileo Gallilei, who decided to calculate the time it takes light to travel 8 km. His research was unsuccessful. James Bradley managed to calculate the approximate value in 1728, who determined the speed at 301 thousand km/s.
What is the speed of light?
Despite the fact that Bradley made fairly accurate calculations, they were able to determine the exact speed only in the 20th century, using modern laser technologies. Advanced equipment made it possible to make calculations corrected for the refractive index of rays, resulting in this value being 299,792.458 kilometers per second. 
Astronomers operate with these figures to this day. Subsequently, simple calculations helped to accurately determine the time that the rays needed to fly around the orbit. globe without the influence of gravitational fields on them.
Although the speed of light is not comparable to earthly distances, its use in calculations is explained by the fact that people are accustomed to thinking in “earthly” categories.
What is a light year equal to?
If we take into account that a light second is equal to 299,792,458 meters, it is easy to calculate that light travels 17,987,547,480 meters in a minute. As a rule, astrophysicists use this data to measure distances inside planetary systems.
For studying celestial bodies on the scale of the Universe, it is much more convenient to take as a basis a light year, which is equal to 9.460 trillion kilometers or 0.306 parsecs. Observing cosmic bodies is the only case when a person can see the past with his own eyes.
It takes many years for light emitted by a distant star to reach Earth. For this reason, watching space objects, you see them not as they are in this moment, and what they were like at the moment of light emission.
Examples of distances in light years
Thanks to the ability to calculate the speed of movement of rays, astronomers were able to calculate the distance in light years to many celestial bodies. Thus, the distance from our planet to the Moon is 1.3 light seconds, to Proxima Centauri - 4.2 light years, to the Andromeda nebula - 2.5 million light years. 
The distance between the Sun and the center of our galaxy takes rays approximately 26 thousand light years, and between the Sun and the planet Pluto - 5 light hours.
One way or another, in my Everyday life 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 It is known 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 exactly the empty 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.
At some point in our lives, each of us asked this question: how long does it take to fly to the stars? Is it possible to make such a flight in one human life, can such flights become the norm of everyday life? There are many answers to this complex question, depending on who is asking. Some are simple, others are more complex. There is too much to take into account to find a complete answer.
Unfortunately, there are no real estimates that would help find such an answer, and this frustrates futurists and interstellar travel enthusiasts. Whether we like it or not, space is very large (and complex) and our technology is still limited. But if we ever decide to leave our “native nest,” we will have several ways to get to the nearest star system in our galaxy.
The closest star to our Earth is the Sun, quite an “average” star according to the Hertzsprung-Russell “main sequence” scheme. This means that the star is very stable and provides enough sunlight so that life can develop on our planet. We know that there are other planets orbiting stars near our solar system, and many of these stars are similar to our own.
In the future, if humanity wishes to leave the solar system, we will have a huge choice of stars that we could go to, and many of them may well have conditions favorable to life. But where will we go and how long will it take us to get there? Keep in mind that this is all just speculation and there are no guidelines for interstellar travel at this time. Well, as Gagarin said, let's go!
Reach for a star
As already noted, the closest star to ours solar system- this is Proxima Centauri, and therefore it makes a lot of sense to start planning an interstellar mission with it. Part of the triple star system Alpha Centauri, Proxima is 4.24 light years (1.3 parsecs) from Earth. Alpha Centauri is, in fact, the most bright Star of the three in the system, part of a close binary system 4.37 light-years from Earth - while Proxima Centauri (the faintest of the three) is an isolated red dwarf 0.13 light-years from the binary system.
And although conversations about interstellar travel evoke thoughts about all kinds of travel, “ faster speed light" (BLS), ranging from warp speeds and wormholes to subspace engines, such theories are either in highest degree are fictional (like the Alcubierre engine), or exist only in science fiction. Any mission into deep space will last for generations.
So, if you start with one of the slowest forms space travel, how long will it take to get to Proxima Centauri?
Modern methods
The question of estimating the duration of travel in space is much simpler if it involves existing technologies and bodies in our Solar System. For example, using the technology used by the New Horizons mission, 16 hydrazine monopropellant engines could get to the Moon in just 8 hours and 35 minutes.
There's also the European Space Agency's SMART-1 mission, which propelled itself toward the Moon using ion propulsion. With this revolutionary technology, a version of which was also used by the Dawn space probe to reach Vesta, the SMART-1 mission took a year, a month and two weeks to reach the Moon.
From fast rocket spacecraft to fuel-efficient ion propulsion, we have a couple of options for getting around local space - plus you can use Jupiter or Saturn as a huge gravitational slingshot. However, if we plan to go a little further, we will have to increase the power of technology and explore new possibilities.
When we talk about possible methods, we are talking about those that involve existing technologies, or those that do not yet exist but are technically feasible. Some of them, as you will see, are time-tested and confirmed, while others still remain in question. In short, they present a possible, but very time-consuming and financially expensive scenario for traveling even to the nearest star.
Ionic movement
Currently, the slowest and most economical form of propulsion is the ion propulsion. A few decades ago, ion propulsion was considered the stuff of science fiction. But in recent years ion engine support technologies have moved from theory to practice, and very successfully. The European Space Agency's SMART-1 mission is an example of a successful mission to the Moon in a 13-month spiral from Earth.
SMART-1 used ion engines on solar energy, in which electricity was collected solar panels and was used to power Hall effect motors. To deliver SMART-1 to the Moon, only 82 kilograms of xenon fuel were required. 1 kilogram of xenon fuel provides a delta-V of 45 m/s. This is an extremely efficient form of movement, but it is far from the fastest.
One of the first missions to use ion propulsion technology was the Deep Space 1 mission to Comet Borrelli in 1998. The DS1 also used a xenon ion engine and consumed 81.5 kg of fuel. After 20 months of thrust, DS1 reached speeds of 56,000 km/h at the time of the comet's flyby.
Ion engines are more economical than rocket technology because their thrust per unit mass of propellant (specific impulse) is much higher. But ion engines take a long time to accelerate spacecraft to significant speeds, and the maximum speed depends on fuel support and power generation volumes.
Therefore, if ion propulsion is used in a mission to Proxima Centauri, the engines must have a powerful energy source (nuclear energy) and large reserves fuel (albeit less than conventional rockets). But if we start from the assumption that 81.5 kg of xenon fuel translates into 56,000 km/h (and there will be no other forms of movement), calculations can be made.
At a top speed of 56,000 km/h, it would take Deep Space 1 81,000 years to travel the 4.24 light years between Earth and Proxima Centauri. In time, this is about 2,700 generations of people. It's safe to say that interplanetary ion propulsion will be too slow for a manned interstellar mission.
But if the ion engines are larger and more powerful (that is, the rate of ion outflow will be much higher), if there is enough rocket fuel to last the entire 4.24 light years, the travel time will be significantly reduced. But there will still be significantly more human life left.
Gravity maneuver
The fastest way to travel in space is to use gravity assist. This technique involves the spacecraft using the relative motion (i.e., orbit) and gravity of the planet to change its path and speed. Gravity maneuvers are an extremely useful technique space flights, especially when using Earth or another massive planet (like gas giant) to speed up.
The Mariner 10 spacecraft was the first to use this method, using the gravitational pull of Venus to propel itself toward Mercury in February 1974. In the 1980s, the Voyager 1 probe used Saturn and Jupiter for gravity maneuvers and acceleration to 60,000 km/h before entering interstellar space.
The Helios 2 mission, which began in 1976 and was intended to explore the interplanetary medium between 0.3 AU. e. and 1 a. e. from the Sun, holds the record for the highest speed developed using a gravitational maneuver. At that time, Helios 1 (launched in 1974) and Helios 2 held the record for the closest approach to the Sun. Helios 2 was launched by a conventional rocket and placed into a highly elongated orbit.
Due to the high eccentricity (0.54) of the 190-day solar orbit, at perihelion Helios 2 was able to achieve a maximum speed of over 240,000 km/h. This orbital speed was developed due to the gravitational attraction of the Sun alone. Technically, Helios 2's perihelion speed was not the result of a gravitational maneuver but its maximum orbital speed, but it still holds the record for the fastest man-made object.
If Voyager 1 were moving towards the red dwarf star Proxima Centauri at a constant speed of 60,000 km/h, it would take 76,000 years (or more than 2,500 generations) to cover this distance. But if the probe reached Helios 2's record speed - a sustained speed of 240,000 km/h - it would take 19,000 years (or more than 600 generations) to travel 4,243 light years. Significantly better, although not nearly practical.
Electromagnetic motor EM Drive
Another proposed method for interstellar travel is the RF Resonant Cavity Engine, also known as EM Drive. Proposed back in 2001 by Roger Scheuer, a British scientist who created Satellite Propulsion Research Ltd (SPR) to implement the project, the engine is based on the idea that electromagnetic microwave cavities can directly convert electricity into thrust.
If traditional electromagnetic motors are designed to move a certain mass (such as ionized particles), specifically this one propulsion system does not depend on the reaction of the mass and does not emit directed radiation. In general, this engine was met with a fair amount of skepticism, largely because it violates the law of conservation of momentum, according to which the momentum of the system remains constant and cannot be created or destroyed, but only changed under the influence of force.
However, recent experiments with this technology have apparently led to positive results. In July 2014, at the 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference in Cleveland, Ohio, NASA advanced propulsion scientists announced that they had successfully tested a new electromagnetic propulsion design.
In April 2015, NASA Eagleworks scientists (part of the Johnson Space Center) said they had successfully tested the engine in a vacuum, which could indicate possible space applications. In July of the same year, a group of scientists from the Space Systems Department of the Dresden University of Technology developed their own version of the engine and observed noticeable thrust.
In 2010, Professor Zhuang Yang from Northwestern Polytechnic University in Xi'an, China, has begun publishing a series of articles about its research into EM Drive technology. In 2012, she reported high input power (2.5 kW) and a recorded thrust of 720 mn. It also conducted extensive testing in 2014, including internal temperature measurements with built-in thermocouples, which showed the system worked.
Based on calculations based on NASA's prototype (which was estimated to have a power rating of 0.4 N/kilowatt), an electromagnetic-powered spacecraft could travel to Pluto in less than 18 months. This is six times less than what was required by the New Horizons probe, which was moving at a speed of 58,000 km/h.
Sounds impressive. But even in this case, the ship on electromagnetic engines will fly to Proxima Centauri for 13,000 years. Close, but still not enough. In addition, until all the i's are dotted in this technology, it is too early to talk about its use.
Nuclear thermal and nuclear electrical motion
Another possibility for interstellar flight is to use a spacecraft equipped with nuclear engines. NASA has been studying such options for decades. In a nuclear rocket thermal movement It would be possible to use uranium or deuterium reactors to heat hydrogen in the reactor, turning it into ionized gas (hydrogen plasma), which would then be directed into the rocket nozzle, generating thrust.
A nuclear-electric powered rocket uses the same reactor to convert heat and energy into electricity, which then powers an electric motor. In both cases the rocket will rely on nuclear fusion or nuclear fission to create thrust rather than the chemical fuel that all modern space agencies run on.
Compared to chemical engines, nuclear engines have undeniable advantages. Firstly, it has virtually unlimited energy density compared to rocket fuel. In addition, a nuclear engine will also produce powerful thrust relative to the amount of fuel used. This will reduce the volume of required fuel, and at the same time the weight and cost of a particular device.
Although thermal engines nuclear energy Until they went into space, their prototypes were created and tested, and even more were proposed.
Yet despite the advantages in fuel economy and specific impulse, the best proposed nuclear thermal engine concept has a maximum specific impulse of 5000 seconds (50 kN s/kg). Using nuclear engines powered by nuclear fission or fusion, NASA scientists could deliver a spacecraft to Mars in just 90 days if the Red Planet is 55,000,000 kilometers from Earth.
But when it comes to traveling to Proxima Centauri, it would take centuries for a nuclear rocket to reach a significant fraction of the speed of light. Then it will take several decades of travel, followed by many more centuries of slowdown on the way to the goal. We are still 1000 years from our destination. What is good for interplanetary missions is not so good for interstellar ones.