For their calculations, astronomers use special units measurements that are not always clear ordinary people. It is understandable, because if cosmic distances were measured in kilometers, then the number of zeros would ripple in the eyes. Therefore, to measure cosmic distances commonly used much large quantities: astronomical unit, light year and parsec.
Quite often used to indicate distances within our native solar system. If you can still express in kilometers (384,000 km), then to Pluto the most close way is approximately 4,250 million km, and this will already be difficult to understand. For such distances, it is time to use the astronomical unit (AU), equal to the average distance from earth's surface to the sun. In other words, 1 a.u. corresponds to the length of the semi-major axis of the orbit of our Earth (150 million km.). Now, if we write that the shortest distance to Pluto is 28 AU, and the most long haul might be 50 AU, it's much easier to imagine.
The next largest is the light year. Although the word "year" is present, one should not think that we are talking about the time. One light year is 63,240 AU. This is the path that a ray of light travels in 1 year. Astronomers have calculated that it takes more than 10 billion years for a beam of light to reach us from the farthest corners of the universe. To imagine this gigantic distance, let's write it down in kilometers: 950000000000000000000000. Ninety-five billion trillion habitual kilometers.
The fact that light does not propagate instantly, but at a certain speed, scientists began to guess since 1676. It was at this time that a Danish astronomer named Ole Römer noticed that the eclipses of one of Jupiter's moons began to lag, and this happened precisely when the Earth was heading in its orbit towards opposite side Sun, the opposite of the one where Jupiter was. Some time passed, the Earth began to return back, and the eclipses again began to approach the previous schedule.
Thus, about 17 minutes of time difference was noted. From this observation, it was concluded that it took 17 minutes for light to travel a distance the length of the diameter of the Earth's orbit. Since the diameter of the orbit was proved to be approximately 186 million miles (now this constant is 939,120,000 km), it turned out that a beam of light traveled at a speed of about 186,000 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 (about 300 km / s). Now, if we calculate the number of seconds in a year and multiply by this number, we get 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 the unit of distance known as the parsec. It is equal to the displacement of the star against the background of others celestial bodies by 1"" when the observer is displaced by 1 radius
In order to understand the meaning of the concept of "light year", you first need to remember the school physics course, especially the section that concerns the speed of light. So the speed of light in a vacuum, where it is not affected various factors, such as gravitational and magnetic fields, suspended particles, refraction of a transparent medium, etc., is 299,792.5 kilometers per second. It must be understood that in this case light means perceived human vision.
Less known units distance measurements are light month, week, day, hour, minute and second.Long enough light was considered an infinite quantity, and the first person to calculate the approximate speed of light rays in a vacuum was the astronomer Olaf Römer in mid-seventeenth century. Of course, his data were very approximate, but the very fact of determining final value speed. In 1970, the speed of light was determined to within one meter per second. More accurate results have not been achieved so far, as there were problems with the error of the meter standard.
Light year and other distances
Since the distances in are huge, measuring them in customary units would be irrational and inconvenient. Based on these considerations, a special light year was introduced, that is, the distance that light travels in the so-called Julian year (equal to 365.25 days). Considering that each day contains 86,400 seconds, it can be calculated that in a year a ray of light covers a distance of several more than 9.4 kilometers. This value seems huge, however, for example, the distance to the nearest star to the Earth, Proxima Centauri, is 4.2 years, and the diameter of the galaxy Milky Way exceeds 100,000 light years, that is, those visual observations that can be made now reflect a picture that existed about a hundred thousand years ago.
A beam of light covers the distance from the Earth to the Moon in about a second, but sunlight reaches our planet for more than eight minutes.
In professional astrophysics, the concept light year rarely used. Scientists mainly operate with units such as the parsec and the astronomical unit. A parsec is the distance to an imaginary point from which the radius of the Earth's orbit is seen at an angle of one arc second (1/3600 of a degree). Medium radius orbit, that is, the distance from the earth to the sun, is called astronomical unit th. A parsec is about 3 light years or 30.8 trillion kilometers. An astronomical unit is approximately equal to 149.6 million kilometers.
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 spaceship 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 go around the whole Earth(≈ 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 school course physics 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 until the existence of speeds is proved, high speed Sveta. That's why academia decided that it would be logical to measure cosmic scales in units that a radio wave travels over certain time intervals (which light, in particular, is).
Distances.
Thus, 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.
Certainly, exact value light year slightly different from what we calculated. But when describing distances to stars in popular science articles, in principle, the highest accuracy is 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 from the third space speed(≈ 16.7 km/s). First light year he will overcome 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 the Milky Way galaxy, having a diameter of approximately 100,000 light years, it will cross in 1 billion 780 million years.
Do you know why astronomers don't use the light year to calculate distances to distant objects in space?
A light year is a non-systemic unit for measuring distances in outer space. It is ubiquitous in popular books and textbooks on astronomy. However, in professional astrophysics, this figure is used extremely rarely and often to determine distances to nearby objects in space. The reason for this is simple: if you determine the distance in light years to distant objects in the Universe, the number will be so huge that it will be impractical and inconvenient to use it for physical and mathematical calculations. Therefore, instead of a light year, professional astronomy uses such a unit of measurement as , which is much more convenient to operate when performing complex mathematical calculations.
Definition of the term
We can find the definition of the term "light year" in any astronomy textbook. A light year is the distance that a ray of light travels in one Earth year. Such a definition may satisfy the amateur, but the cosmologist will find it incomplete. He will notice that a light year is not just the distance that light travels in a year, but the distance that a beam of light travels in 365.25 Earth days in vacuum, without being affected by magnetic fields.
A light year is 9.46 trillion kilometers. This is the distance a ray of light travels in a year. But how did astronomers achieve this? exact definition beam path? We will talk about this below.
How is the speed of light determined?
In ancient times, it was believed that light propagates in the universe instantly. However, beginning in the seventeenth century, scholars began to doubt this. Galileo was the first to doubt the above proposed statement. It was he who tried to determine the time during which a ray of light travels a distance of 8 km. But due to the fact that such a distance was negligible for such a value as the speed of light, the experiment ended in failure.
The first major shift in this issue was the observation of the famous Danish astronomer Olaf Römer. In 1676, he noticed the difference in the time of an eclipse depending on the approach and removal of the Earth to them in outer space. This observation Roemer has successfully connected with the fact that the farther the Earth moves away from, the longer it takes the light reflected from them to travel the distance to our planet.
essence this fact Roemer caught exactly, but he did not succeed in calculating the reliable value of the speed of light. His calculations were wrong, because in the seventeenth century he could not have accurate data on the distance from the Earth to other planets in the solar system. These data were determined somewhat later.
Further advances in research and determination of the light year
In 1728, the English astronomer James Bradley, who discovered the effect of stellar aberration, was the first to calculate the approximate speed of light. He determined its value at 301 thousand km / s. But this value was inaccurate. More advanced methods for calculating the speed of light have been produced regardless of space bodies- on the ground.
Observations of the speed of light in vacuum using a rotating wheel and a mirror were made by A. Fizeau and L. Foucault, respectively. With their help, physicists managed to get closer to the real value of this quantity.
Accurate speed of light
Scientists managed to determine the exact speed of light only in the last century. Based on Maxwell's theory of electromagnetism, with the help of modern laser technology and calculations, corrected for the refractive index of the ray stream in the air, scientists were able to calculate the exact value of the speed of light 299,792.458 km / s. This value is still used by astronomers. Further, to determine the light day, month and year was already a matter of technology. By simple calculations, scientists got the figure of 9.46 trillion kilometers - that is how long it would take for a beam of light to fly around the length of the earth's orbit.
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1 kilometer [km] = 1.0570008340247E-13 light year [St. G.]
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More about length and distance
General information
Length is largest dimension body. IN three-dimensional space length is usually measured horizontally.
Distance is a measure of how far two bodies are from each other.
Distance and length measurement
Distance and length units
In the SI system, length is measured in meters. Derived quantities such as kilometer (1000 meters) and centimeter (1/100 meter) are also widely used in the metric system. In countries that do not use the metric system, such as the US and the UK, units such as inches, feet, and miles are used.
Distance in physics and biology
In biology and physics, lengths are often measured much less than one millimeter. For this, a special value, a micrometer, has been adopted. One micrometer is equal to 1×10⁻⁶ meters. In biology, micrometers measure the size of microorganisms and cells, and in physics, the length of the infrared electromagnetic radiation. A micrometer is also called a micron and is sometimes, especially in English literature, denoted Greek letterµ. Other derivatives of the meter are also widely used: nanometers (1×10⁻⁹ meters), picometers (1×10⁻¹² meters), femtometers (1×10⁻¹⁵ meters), and attometers (1×10⁻¹⁸ meters).
Distance in navigation
Shipping uses nautical miles. One nautical mile is equal to 1852 meters. Initially, it was measured as an arc of one minute along the meridian, that is, 1/(60 × 180) of the meridian. This made latitude calculations easier, since 60 nautical miles equaled one degree of latitude. When distance is measured in nautical miles, speed is often measured in nautical knots. One maritime knot equal to speed movement of one nautical mile per hour.
distance in astronomy
In astronomy, long distances are measured, so special quantities are adopted to facilitate calculations.
astronomical unit(au, au) is equal to 149,597,870,700 meters. The value of one astronomical unit is a constant, that is, constant. It is generally accepted that the Earth is located at a distance of one astronomical unit from the Sun.
Light year equals 10,000,000,000,000 or 10¹³ kilometers. This is the distance light travels in a vacuum in one Julian year. This value is used in popular science literature more often than in physics and astronomy.
Parsec approximately equal to 30,856,775,814,671,900 meters or approximately 3.09 × 10¹³ kilometers. One parsec is the distance from the sun to another astronomical object, such as a planet, star, moon, or asteroid, with an angle of one arcsecond. One arc second is 1/3600 of a degree, or about 4.8481368 mrad in radians. Parsec can be calculated using parallax - the effect of a visible change in the position of the body, depending on the point of observation. During measurements, a segment E1A2 (in the illustration) is laid from the Earth (point E1) to a star or other astronomical object (point A2). Six months later, when the Sun is on the other side of the Earth, a new segment E2A1 from the new position of the Earth (point E2) to the new position in space of the same astronomical object (point A1). In this case, the Sun will be at the intersection of these two segments, at point S. The length of each of the segments E1S and E2S is equal to one astronomical unit. If we postpone the segment through the point S, perpendicular to E1E2, it will pass through the intersection point of the segments E1A2 and E2A1, I. The distance from the Sun to point I is the SI segment, it is equal to one parsec when the angle between the segments A1I and A2I is two arcseconds.
On the image:
- A1, A2: apparent star position
- E1, E2: Earth position
- S: position of the sun
- I: point of intersection
- IS = 1 parsec
- ∠P or ∠XIA2: parallax angle
- ∠P = 1 arc second
Other units
league- an obsolete unit of length used earlier in many countries. In some places it is still used, for example, in the Yucatan Peninsula and in rural areas Mexico. This is the distance a person walks in an hour. Marine League - Three nautical miles, about 5.6 kilometers. Lie - a unit approximately equal to the league. IN English language both leagues and leagues are called the same, league. In literature, the league is sometimes found in the title of books, such as "20,000 Leagues Under the Sea" - famous novel Jules Verne.
Elbow- old value equal to the distance from the tip of the middle finger to the elbow. This value was widely used in ancient world, in the Middle Ages, and until modern times.
Yard used in British imperial system measures and is equal to three feet or 0.9144 meters. In some countries, such as Canada, where the metric system Yards are used to measure the fabric and length of swimming pools and sports fields such as golf and football fields.
Meter Definition
The definition of the meter has changed several times. The meter was originally defined as 1/10,000,000 of the distance from North Pole to the equator. Later, the meter was equal to the length of the platinum-iridium standard. Later, the meter was equated to the wavelength of the orange line. electromagnetic spectrum krypton atom ⁸⁶Kr in vacuum multiplied by 1 650 763.73. Today, a meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
Computing
In geometry, the distance between two points, A and B, with coordinates A(x₁, y₁) and B(x₂, y₂) is calculated by the formula:
and within a few minutes you will receive an answer.Calculations for converting units in the converter " Length and distance converter' are performed using the functions of unitconversion.org .
