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How Long Is A Parsec (And Why)?

Exact Answer: 3.25 Light Years

A Parsec is a mathematical unit of length. This measure of length is used to describe and measure the large distances between two astronomical objects present outside the solar system. The symbol for parsec is pc and it is also the most preferred unit of measurement in fields like astronomy and astrophysics.

The word “parsec” is an abbreviation used for the parallax of one second. The term was first coined by British scholar Herbert Hall Turner and is interpreted as the distance at which one au subtends to an angle of one arcsecond. Although shorter distances in the milky way galaxy can be denoted by parse, those which are outside the galaxy can be denoted in its multiples like kiloparsec.

How Long Is A Parsec?

One Unit in parsec Value of One parsec in other units
One parsec1/tan(1″) au
One parsec3.26 light-years
One parsec19.2 trillion miles
One parsec3.086e + 16 meters
One parsec3.086e +13 kilometers
One parsec3.086e + 18 centimeters
One parsec3.086e + 19 millimeters
One parsec3.086e + 22 micrometers
One parsec3.375e + 16 yards
One parsec 1.215e + 18 inches
One parsec 1.012e + 17 feet

The value of one unit of parsec is determined by its mathematical formulas. Parsec can be described in the terms of the astronomical unit for basic reference. From here onwards, the value of parsec can be converted to infer values in other units of measurements.

In terms of the astronomical unit, one parsec is equal to 1/tan(1″) astronomical units. When the same measure is converted in a light year, the figure stands at 3.26 light-years. In miles, the value of one parsec stands at 19.2 trillion miles. ?

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The value of the same distance, when stated in meter terms, is 3.086e+ 16 meters. When one parsec is converted to a kilometer, a greater denomination of meters, its value stands at 3.086e + 13 kilometers. However, the sub-units of meter, centimeter, millimeter and micrometer has the values of 3.086e + 18 centimeters, 3.086e + 19 millimeters, and 3.086e + 22 micrometers respectively.

When one unit of parsec is converted to the imperial system of measurement, its value in yards is 3.375e + 16 yards. The same unit when referred to in inches stands at 1.215e + 18 inches. One parsec is equal to 1.012e + 17 feet.

Why Is A Parsec So Long?

One unit of parsec is defined as 3.26 light-years after proper calculations. There have been studies on the topic which explain the reason behind this particular length of a unit of parsec.

As is well known, our planet Earth revolves around the sun in its own orbit. It completes one full circle which marks the completion of a year. Over the course of months, it may appear to people on Earth as if the star is moving due to the continued circling of Earth. This effect is termed the parallax effect.

When compared after a period of six months, the position of stars may be vastly different as the Earth would have completed half rotation. When these two positions are compared, it would be noticed that they for a sort of triangle with the point from which the stars are seen. This point gives the angle.

This results in the parallax angle which is defined as half the angle of the apex of the triangle. This parallax angle further helps to reach the value of a unit of parsec. According to the definition of parsec, one parsec represents the distance between the sun and the star so that the parallax angle is 1″.

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This gives the value of one parsec as 3.36 light-years.


The calculation of parsec gives the distance between the sun and the star so that the angle of parallax is 1″. This mathematical unit measures large astronomical distances between objects outside the solar system. With the help of these measures, the distance between Proxima Centauri and the sun has been determined at 1.3 parsecs.

After much research and study, the value of one unit of parsec is determined as 1/tan(1″) au or in terms of light-years, 3.26 light-years. There are various formulas and theorems in place related to this unit of measurement of length. These formulas have immensely eased the conversion of values from parsec to any other unit.


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