Our large measures of length - kilometer, nautical mile (1852 m) and geographical mile (equal to 4 nautical miles), sufficient for measurements on the globe, turn out to be too insignificant for celestial measurements. Measuring celestial distances with them is as inconvenient as measuring the length of a railway with millimeters; The distance, for example, of Jupiter from the Sun in kilometers is expressed as 780 million, while the length of the October Road in millimeters is expressed as 640 million.
To avoid dealing with long rows of zeros at the end of numbers, astronomers use larger units of length. For measurements, for example, within the solar system, the unit of length is considered to be the average distance from the Earth to the Sun (149,600,000 km). This is the so-called “astronomical unit”. In such measures, the distance of Jupiter from the Sun is 5.2, Saturn - 9.54, Mercury - 0.387, etc.
But for the distances of our Sun to other suns, the given measure is now too small. For example, the distance to the star closest to us (to the so-called Proxima in the constellation Centaurus, a reddish star of 11th magnitude) is expressed in these units by the following number:
And this is only the nearest star, others are located much further away. Larger units introduced made it much easier to remember and handle such numbers. In astronomy there are the following gigantic units of distances: the light year and the parsec, which successfully displaces it.
A light year is the distance traveled in empty space by a beam of light in a year of time. We will understand how great this measure is by remembering that sunlight reaches the Earth in just 8 minutes. A light year, therefore, is as many times greater than the radius of the earth's orbit as a year is greater than 8 minutes. In kilometers, this measure of length is expressed by the number
9 460 000 000 000,
i.e., a light year is about 9 1/2 billion km.
The origin of another unit of stellar distances, which astronomers resort to more readily, is the parsec. A parsec is the distance that must be removed so that the half-diameter of the Earth's orbit is visible at an angle of one arcsecond. The angle at which the half-diameter of the Earth's orbit is visible from a star is called in astronomy the annual parallax of this star. From the combination of the words “parallax” and “second” the word “parsec” is formed. The parallax of the above-named star Alpha Centauri is 0.76 seconds; It’s easy to figure out that the distance of this star is 1.31 parsecs. It is easy to calculate that one parsec should contain 206,265 distances from the Earth to the Sun. The relationship between parsec and other units of length is:
1 parsec = 3.26 light years = 30,800,000,000,000 km.
Here are the distances of several bright stars, expressed in parsecs and light years:
These are stars relatively close to us. You will understand the order of their “closeness” when you remember that to express the given distances in kilometers, you need to increase each of the numbers in the first column by 30 billion times (meaning a billion is a million million). However, a light year and a parsec are not yet the largest measures used in stellar science. When astronomers began to measure the distances and sizes of star systems, that is, entire universes consisting of many millions of stars, an even larger measure was needed. It was formed from a parsec, just as a kilometer is formed from a meter: a kiloparsec was formed, equal to 1000 parsecs, or 30,800 billion km. In these measures, for example, the diameter of the Milky Way is expressed as 30, and the distance from us to the Andromeda nebula is about 300.
But even a kiloparsec soon turned out to be not a large enough measure; a megaparsec containing a million parsecs had to be introduced. So, here are the stellar length measures:
There is no way to visualize a megaparsec. Even if we reduce the kilometer to the thickness of a hair (0.05 mm), then the megaparsec will still exceed the power of human imagination, since it will become equal to 1/2 billion km - 10 times the distance from the Earth to the Sun.
angular sec unds and denotes the distance to the object, [quarter]year parallax which is equal to one arcsecond.According to an equivalent definition, a parsec is the distance from which average radius of the earth's orbit(equal to 1 a.e.), perpendicular to the line of sight, visible at an angle of one arcsecond (1″).
1 pc= a.u. ≈ 206 264,8 a.e. = 3.0856776 10 16 = 30,8568 trillion km (petameters) = 3.2616 light years.Multiple units are also used: kiloparsec (kpc), megaparsec (Mpc), gigaparsec (Gpc).
Some distances
see also
Notes
Literature
- Parsec. Article from the Great Soviet Encyclopedia.
Wikimedia Foundation. 2010.
Synonyms:See what "Parsec" is in other dictionaries:
- (pc, rs), a unit of length used in astronomy; 1 pc=206,265 a. e. = 3.0857 1016 m. A star located at a distance of 1 pc has an annual parallax equal to 1. Definition of parsec. Physical encyclopedic dictionary. M.: Soviet... ... Physical encyclopedia
- (denoted pc (SI) or ps), the distance at which the star would have a PARALLAX equal to one arcsecond. A parsec is equal to 3.2616 light years, 206,265 astronomical units, or 3.08631013 km... Scientific and technical encyclopedic dictionary
Modern encyclopedia
- (short for parallax and second) a unit of length used in astronomy. Equal to the distance at which the parallax is 1?; denoted pk (SI), former designation ps. 1 pc = 206,265 a. e. = 3.263 light years = 3.086.1016 m... Big Encyclopedic Dictionary
PARSEK, parseka, husband. (composed of an abbreviation for the word parallax and an abbreviation for the word second) (astro.). A unit of measurement for stellar distances, equal to the distance for which the annual parallax is equal to one second. Ushakov's explanatory dictionary. D.N.... ... Ushakov's Explanatory Dictionary
Noun, number of synonyms: 1 unit (830) ASIS Dictionary of Synonyms. V.N. Trishin. 2013… Synonym dictionary
parsec- a, m. parsec m. abbreviation parallax + second. astr. A unit of measurement for stellar distances equal to 3.26 light years. SIS 1954. A unit of measurement of distances in astronomy, equal to the distance for which the annual parallax is equal to one... ... Historical Dictionary of Gallicisms of the Russian Language
parsec- parsec, gen. pl. parsecs... Dictionary of difficulties of pronunciation and stress in modern Russian language
parsec- parallax second... Dictionary of abbreviations and abbreviations
Parsec- (short for parallax and second), a unit of length used in astronomy. Equal to the distance at which the parallax (in this case, the angle at which a segment 1 astronomical unit long is visible) is 1. 1 pc=206265 a. e.=3.263… … Illustrated Encyclopedic Dictionary
PARSEC- a non-systemic unit of length, acceptable and often used in astronomy along with SI units; designated pc. 1 pc is equal to the distance from which the half-diameter of the earth's orbit (»75,000 million km) is visible at an angle of 1 (1 arcsecond); 1 pc » 3.26… … Big Polytechnic Encyclopedia
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1 parsec [pc] = 3.26156377694428 light year [sa. G.]
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More about length and distance
General information
Length is the largest measurement of the body. In three-dimensional space, length is usually measured horizontally.
Distance is a quantity that determines how far two bodies are from each other.
Measuring distance and length
Units of distance and length
In the SI system, length is measured in meters. Derived units such as kilometer (1000 meters) and centimeter (1/100 meter) are also commonly used in the metric system. Countries that do not use the metric system, such as the US and UK, use units such as inches, feet and miles.
Distance in physics and biology
In biology and physics, lengths are often measured at much less than one millimeter. For this purpose, a special value has been adopted, the micrometer. One micrometer is equal to 1×10⁻⁶ meters. In biology, the size of microorganisms and cells is measured in micrometers, and in physics, the length of infrared electromagnetic radiation is measured. A micrometer is also called a micron and is sometimes, especially in English literature, denoted by the Greek letter µ. 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).
Navigation distance
Shipping uses nautical miles. One nautical mile is equal to 1852 meters. It was originally measured as an arc of one minute along the meridian, that is, 1/(60x180) 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 knots. One sea knot equals a speed of one nautical mile per hour.
Distance in astronomy
In astronomy, large 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, a constant value. It is generally accepted that the Earth is located at a distance of one astronomical unit from the Sun.
Light year equal to 10,000,000,000,000 or 10¹³ kilometers. This is the distance that light travels in a vacuum in one Julian year. This quantity 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 arcsecond is 1/3600 of a degree, or approximately 4.8481368 microrads in radians. Parsec can be calculated using parallax - the effect of visible changes in body position, depending on the observation point. When making measurements, lay a segment E1A2 (in the illustration) 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 is laid 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 plot a segment through point S, perpendicular to E1E2, it will pass through the intersection point of segments E1A2 and E2A1, I. The distance from the Sun to point I is segment SI, it is equal to one parsec, when the angle between segments A1I and A2I is two arcseconds.
On the image:
- A1, A2: apparent star position
- E1, E2: Earth position
- S: Sun position
- I: point of intersection
- IS = 1 parsec
- ∠P or ∠XIA2: parallax angle
- ∠P = 1 arcsecond
Other units
League- an obsolete unit of length previously used in many countries. It is still used in some places, such as the Yucatan Peninsula and rural areas of Mexico. This is the distance a person travels in an hour. Sea League - three nautical miles, approximately 5.6 kilometers. Lieu is a unit approximately equal to a league. In English, both leagues and leagues are called the same, league. In literature, league is sometimes found in the title of books, such as “20,000 Leagues Under the Sea” - the famous novel by Jules Verne.
Elbow- an ancient value equal to the distance from the tip of the middle finger to the elbow. This value was widespread in the ancient world, in the Middle Ages, and until modern times.
Yard used in the British Imperial system and is equal to three feet or 0.9144 meters. In some countries, such as Canada, which adopts the metric system, yards are used to measure fabric and the length of swimming pools and sports fields such as golf courses and soccer fields.
Definition of meter
The definition of meter has changed several times. The meter was originally defined as 1/10,000,000 of the distance from the North Pole to the equator. Later, the meter was equal to the length of the platinum-iridium standard. The meter was later equated to the wavelength of the orange line of the electromagnetic spectrum of the krypton atom ⁸⁶Kr in a 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.
Computations
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 unitconversion.org functions.
The simpler the words, the more there are. I warned you - now don't complain!
The Earth has an elliptical orbit. An ellipse, unlike a circle, does not have a “radius”, but has two “semi-axes” of different lengths - major and minor. Accordingly, there are two points in the earth's orbit that lie on the major axis and are the most distant from each other compared to any other pair of orbital points. Exactly in the middle of the segment between these points we draw a perpendicular to the plane in which the orbit lies (the ecliptic plane). An observer moving along a perpendicular will see the Earth's orbit from different angles. That is, if we draw rays from the observer’s location to the two previously mentioned points in the Earth’s orbit, the angle between the rays will depend on the distance to the ecliptic plane. Very close to the plane, the rays form a very obtuse angle (almost 180°). Very far - very sharp (almost 0°). And there is a distance at which this angle will be equal to exactly 2" (two arc seconds; one second is equal to 1°/3600). This is a parsec.
For a stationary alien sitting on the above-described perpendicular one parsec from the Earth and able to somehow see it (this is quite difficult, since the Earth is not bright enough for such a distant observer), the Earth will change its apparent location slightly due to its orbital movement. The displacement angle between the two extreme visible positions of the Earth will be exactly 2" (we specifically placed the alien at exactly this distance in order to obtain such a displacement angle). And relative to a certain "average" visible location, the Earth will move a maximum of 1" (half from 2"). An alien may say that the "annual trigonometric parallax" of the Earth is 1" (one arcsecond). And call the distance to Earth a “parsec” (PARALLAX - SECOND).
The parsec was needed, of course, not by aliens, enthusiastically observing the Earth from perpendicular to the ecliptic, but by terrestrial astronomers. The stars are so far away from us that their own movement does not lead to a change in position in the sky even in a year. But they seem to “rotate” in the sky in a circle due to the rotation of the Earth around its axis (one revolution per day). In addition to this, the stars ADDITIONALLY “move” across the sky due to the movement of the Earth in its orbit, although this is hardly noticeable (for complete happiness, the influence of the earth’s atmosphere and vibrations of the earth’s axis will also be added, but let’s say we took this into account and overcame it). If you try very hard, you can identify this subtle (against the background of daily “rotation” and other interference) movement and measure the annual trigonometric parallax of the star. And if the star were located near the above-described perpendicular to the ecliptic and had an annual parallax of 1", then it would be (damm!) exactly one parsec from us. After all, in the reference frame associated with the Earth, it is not the Earth moving in an elliptical orbit , and for some reason the rest of the world makes a similar movement, but in the opposite direction. Accordingly, for an earthly astronomer watching the above-described alien (or the star next to it), this is the alien (or the star next to it): 1) why- then it rotates around the Earth at a wild speed (with a full revolution in 1 day) and 2) additionally moves along an elliptical orbit (with a full revolution in one year and semi-axes, like the earth’s), parallel to the ecliptic plane.
The distance to the remaining stars can also be easily calculated (only geometry with trigonometry and nothing more) in parsecs, if you can measure their annual parallax and (additionally) take into account their position in the sky. The parsec itself is equal (by definition and from trigonometry) to the cotangent of 1", multiplied by the semi-major axis of the earth's orbit (by the "astronomical unit"). The cotangent of the small angle is equal to one divided by the angle itself in radians. 180° is pi radians, 1° is pi/180 radians, 1"=1°/3600=pi/(180×3600). Cotangent 1" is 180×3600/pi≈206.000. Accordingly, the parsec is approximately equal to (slightly more) 206 thousand “astronomical units” (semimajor axes of the earth’s orbit). And since we know the parameters of the earth’s orbit (including its semimajor axis ), the parsec itself can be expressed in other units of distance (meters, light years, etc.) - this is approximately 3.2 light years. The stars closest to us have an annual trigonometric parallax of less than (but on the order of) 1" and, accordingly, are located at a distance greater (but on the order of) one parsec.