The distance between space objects is not comparable with the earth, and one could "drown in zeros" by measuring them in kilometers. Therefore, astronomers needed special units for measuring distances, and one of them is the parsec.

What does this word mean

The word "parsec" is made up of two words: parallax and.

A second in this context is not not time, but an angle. As you know, angles are measured in degrees, each of which is divided into 60 parts, called , and each is subdivided into 60 seconds.

Parallax is the displacement of an object relative to the background, determined by the position of the observer. Astronomers deal with three types of parallax - daily, annual and secular. With regard to the parsec, it is the annual one that is of interest.

By determining the annual parallax of a particular star, astronomers calculate what is the distance from the Earth to it. To do this, you need to build an imaginary right triangle. The hypotenuse in it will be the distance from this star to the Sun, and one of the legs will be the semi-major axis of the Earth's orbit. The size of the angle in this triangle corresponding to the star is the annual parallax.
The distance to a star at which the size of this angle is one second is called a parsec. The international of this unit is pc, and in Russian it is referred to as pc.

Why parsec

When talking about large distances on a cosmic scale, they are often measured in. This unit of measurement corresponds to the distance that a light beam travels in a year, and it is equal to 9,460,730,472,580.8 km. An impressive amount, but a parsec is even larger!

A parsec is 3.2616 light years, which is 30.8568 trillion km. It is this unit of measurement, and not the light year, that professional astronomers usually use. Distance in light years is more often indicated in popular science publications or science fiction novels and films.

But even such a unit of measurement was not enough for the needs of space exploration. I had to introduce units equal to a million parsecs - kiloparsec (kpc) and megaparsec (Mpc).

Thus, the distance that the heroes of the "Secrets of the Third Planet" were offered to overcome turns out to be very impressive. 100 pc is more than 326 light years! However, modern astronomy knows more significant distances. For example, the distance to the Virgo cluster, the closest cluster of galaxies to Earth, is 18 Mpc.

Image source: mattbodnar.com

Because of its uniqueness, every person who watched this cartoon remembered this word.

“It’s not far here, a hundred parsecs!”, - thus Gromozeka, one of the heroes of the “Secrets of the Third Planet”, reported the distance to the planet, which he recommended to fly to prof. Seleznev and his team.

However, few people know what exactly parsec means, what distance we are talking about and how far the characters of the popular cartoon were forced to fly.

The meaning of the term "parsec"

This term was derived from the words "parallax" and "second", which here represents not a unit of time, but an arc second - an off-system astronomical unit, which is identical to a second of a flat angle.

Parallax is a change in the location of a celestial body depending on where the observer is located.

Modern astronomy distinguishes the following types of parallax:

Daily- the difference in directions to a certain luminary, both in the geocentric and topocentric direction. This angle directly depends on the height of the celestial body above the horizon.
At annual parallax changes in direction to a certain object directly depend on the rotation of the Earth around the Sun.
Concerning secular parallax, then it makes it possible to determine the difference in the direction to the celestial body, depending on their movements in the Galaxy.

Parsec - the meaning of the term

Speaking in an accessible language, then "parsec" is a unit of change in the distance between celestial bodies located outside the solar system. The parsec is usually used to calculate the distance within the Milky Way. Basically, these are multiple units: kiloparsecs, megaparsecs and gigapersecs. Sub-multiple units are usually not used because it is more comfortable to use standard astronomical units instead.
A parsec greatly simplifies calculations for astronomers, because it is much easier to say that one and a half parsecs are from the Sun to a certain star than more than 46 trillion km.

Who invented the parsec?

in 1838 the German Friedrich Bessel was the first to achieve success in measuring the distances to objects in space. He was the first to make accurate calculations of the Cygnus star of 61 annual parallax. To calculate the distance from this star, Bessel used the old method, calculating the difference in angles obtained after taking two measurements.

Determining the distance to stars by the parallax method. Image source: bigslide.ru

First, measurements were made when the Earth was located relative to the Sun on one side, and six months later, repeated measurements were made (when the Earth turned to the Sun on the other side).

However, the term "parsec" itself appeared only in 1913 thanks to the English astronomer Herbert Turner.

How is a parsec calculated and what is it equal to?

Schematic drawing of a parsec (not to scale) Image source: wikipedia.org

One parsec is defined as the distance at which one astronomical unit (the average distance between the Earth and the Sun) represents the angle of one arc-second.

An annual parallax is used to calculate the parsec. When using an imaginary triangle with right angles, a parsec is the distance to a star, assuming its parallax is 1 arcsecond.
A parsec is 3.26 light years or about 30 trillion km. It is one of the first ways to determine the distances to stars and is denoted as "pc"

The essence of the parsec is to use the principle of parallax to determine the distance to celestial bodies in space due to their tiny shift as the Earth moves around the Sun.

Some distances to space objects in parsecs:

The distance to the closest star to the Sun - Proxima Centauri - 1.3 parsecs.

The distance from the Sun to the center of the Milky Way is about 8 kiloparsecs.

The distance from the Sun to the Andromeda Nebula is 0.77 megaparsecs.

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angular sec und and denotes the distance to an object whose [quarter]yearly parallax is one arc second.

By equivalent definition, a parsec is the distance from which mean radius of the earth's orbit(equal to 1 AU) perpendicular to the line of sight, seen at an angle of one arc second (1″).

1 pc= a.u. ≈ 206 264.8 a.u.= 3.0856776 10 16 = 30.8568 trillion km(petameters) = 3.2616 light years.

Multiple units are also used: kiloparsec (kpc, kpc), megaparsec (Mpc, Mpc), gigaparsec (Gpc, Gpc).

Some distances

see also

Notes

Literature

• Parsec. Article from the Great Soviet Encyclopedia.

Wikimedia Foundation. 2010 .

Synonyms:

• Kilometer
• supermalloy

See what "Parsec" is in other dictionaries:

PARSEC- (pc, rs), a unit of length used in astronomy; 1 pc \u003d 206 265 a. e. = 3.0857 1016 m. A star located at a distance of 1 pc has an annual parallax equal to 1 . The definition of a parsec. Physical Encyclopedic Dictionary. M .: Soviet ... ... Physical Encyclopedia

PARSEC- (denoted pc (SI) or ps), the distance at which the star would have a PARALLAX equal to one arc second. A parsec is equal to 3.2616 light years, 206,265 astronomical units, or 3.08631013 km... Scientific and technical encyclopedic dictionary

PARSEC Modern Encyclopedia

PARSEC- (short for parallax and second) a unit of length used in astronomy. Equal to the distance at which the parallax is 1?; denoted pc (SI), the former designation ps. 1 pc \u003d 206 265 a. e. \u003d 3.263 light years \u003d 3.086.1016 m ... Big Encyclopedic Dictionary

PARSEC- PARSEC, parsec, husband. (composed of the abbreviation of the word parallax and the abbreviation of the word second) (aster). A unit of measurement for the distances of stars, equal to the distance for which the annual parallax is one second. Explanatory Dictionary of Ushakov. D.N.… … Explanatory Dictionary of Ushakov

parsec- n., number of synonyms: 1 unit (830) ASIS synonym dictionary. V.N. Trishin. 2013 ... Synonym dictionary

parsec- a, m. parsec m. reduction parallax + second. aster. A unit of stellar distances equal to 3.26 light years. SIS 1954. A unit of distance 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, genus. pl. parsecs ... Dictionary of pronunciation and stress difficulties in modern Russian

parsec- parallax second... Dictionary of abbreviations and abbreviations

Parsec- (short for parallax and second), a unit of length used in astronomy. It is equal to the distance at which the parallax (in this case, the angle at which a segment of 1 astronomical unit is visible) is 1 . 1 pc \u003d 206265 a. e. \u003d 3.263 ... ... Illustrated Encyclopedic Dictionary

PARSEC- an off-system unit of length, acceptable and often used in astronomy along with SI units; denoted by 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 arc second); 1 pc » 3.26… … Great Polytechnic Encyclopedia

The parsec is a cosmic unit of measure used by astronomers to determine the distance to very distant objects in the universe.

The parsec (abbreviated as "parallax second") is a non-systemic unit of measurement used in cosmology to measure distances to particularly distant objects in outer space. This unit performs not only a practical function - it helps to calculate the distance to a particular object in the Universe, but also creates a kind of comfort for astronomers. Judge for yourself, it is much easier to say that the distance from the Sun to the nearest star is 1.3 parsecs than that it is 40.7 trillion kilometers. A person who would regularly operate with numbers with such a huge number of zeros would sooner or later go crazy. Thus, by inventing the parsec, scientists have greatly simplified the computational processes in astronomy.

The parsec is a popular unit of measurement in astrophysics. Fans of this science are well aware that it is equal to 3.2616 light years. Many of them can freely name the distance to one or another distant object in parsecs. But, unfortunately, not everyone understands how this unit of measurement came into being and how to calculate it correctly.

Discovery history

While distances to nearby objects in space can be measured with a radio telescope to within a few centimeters, measuring distances to distant corners of the universe is much more difficult. However, scientists needed to find a way to calculate this value and they decided to use the horizontal parallax method, which is well known in geometry.

The essence of the horizontal parallax method is simple: if you look at a distant object from different places, then against the background of other, more distant objects, it will change its position. Knowing the distance between the places from which observation is carried out, as well as the angle of displacement of the object against the background of distant objects, it is possible to calculate the distance to it by geometric calculations. Astronomers decided to use this axiom; it served as the basis for the discovery of a new unit of measurement - the parsec.

How to determine a parsec

Let's say you're looking at a star and want to determine its distance in parsecs. But for this you need to know what a distance of 1 parsec is. This distance represents the displacement of a celestial body against the background of other, more distant objects by an angle equal to one arc second when the observer moves half the diameter of the earth's orbit.

To some, this definition may seem difficult to understand. In fact, the essence of the definition of a parsec is not so difficult to understand. Returning to our star, the distance in parsecs to which we want to determine, we will have to make two observations of this object from different points in the earth's orbit. This can be done without any space instruments, but simply by waiting for the Earth itself to pass half of its annual path and become on the opposite side of the Sun.

Knowing the length between the points from which the observations were made (it is equal to 1 astronomical unit - the distance of the Earth from the Sun or the radius of the Earth's orbit), as well as the displacement of the star against the background of more distant stars and galaxies, we can calculate the distance to it. If in the observed range the star has shifted by 1 arc second, the distance to it is one parsec, if it has shifted by half a second, two parsecs. Contrary to conjecture, the smaller the parallax (displacement) of a celestial body, the more parsecs to it.

For their calculations, astronomers use special units of measurement that are not always clear to 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, it is customary to use much larger quantities: an astronomical unit, a light year, and a parsec.

Quite often used to indicate distances within our own solar system. If you can still express it in kilometers (384,000 km), then the closest way to Pluto is about 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 the 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 you write that the shortest distance to Pluto is 28 AU, and the longest path can be 50 AU, this is much easier to imagine.

The next largest is the light year. Although the word “year” is present, you should not think that it is about 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 the opposite side of the Sun, the opposite of 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 count 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 other celestial bodies by 1 "" when the observer is displaced by 1 radius