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# What is parsec

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"Not far, a hundred parsecs!" - So one of the characters in the cartoon "The Mystery of the Third Planet" marked the distance from the Moon to the planet, where he advises to go to Professor Seleznev and his companions.

How far did the heroes have to fly?

The distance between space objects is notComparable with the terrestrial, and one could "drown in zeros", measuring them in kilometers. That's why astronomers needed special units for measuring distances, and one of them is parsec.

## What does this word mean

The word "parsec" is an abbreviation composed of two words: parallax and second.
The second in this context is not a unitMeasure not the time, but the angle. As you know, the angles are measured in degrees, each of which is divided into 60 parts, called minutes, and every minute is divided into 60 seconds.
Parallax is the displacement of an object relative toBackground determined by the position of the observer. Astronomers deal with three kinds of parallax - the daily, the annual and the century. With regard to parsec, interest is represented by a year-old.
Defining the annual parallax of a particular star,Astronomers calculate what is the distance from the Earth to it. To do this, we need to construct an imaginary rectangular triangle. The hypotenuse in it will be the distance from this star to the Sun, and one of the legs is the semimajor axis of the Earth's orbit. The size of the angle in this triangle corresponding to the star is the one-year parallax.
The distance to the star at which the size of this angle is one second is called the parsec. International designation of this unit is pc, and in the Russian-language literature it is designated as pc.

## What is parsec

When talking about large distances in spaceScale, often measure them in light years. This unit of measure corresponds to the distance that the light beam will pass in a year, and it equals 9,460,730,472,580.8 km. An impressive amount, but parsec even more!
Parsek - this is 3.2616 light years, otherIn words, this 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 often indicated in popular science publications or fantasy novels and films.
But even this unit of measurement was not enough for the needs of space exploration. It was necessary to introduce units equal to a thousand and a million parsecs - kiloparsec (kpc) and megaparsec (Mpc).
Thus, the distance offeredTo overcome the heroes of "Secrets of the Third Planet", is very impressive. 100 pc is more than 326 light years! However, modern astronomy knows and more significant distances. For example, the distance to the Virgo cluster - the closest cluster of galaxies to the Earth - is 18 Mpc.