# parsec, pc (unit)
This page documents an [OPTIMADE](https://www.optimade.org/) [Unit Definition](https://schemas.optimade.org/#definitions). See [https://schemas.optimade.org/](https://schemas.optimade.org/) for more information.
**ID: [`https://schemas.optimade.org/defs/v1.2/units/si/1970/accepted/parsec`](https://schemas.optimade.org/defs/v1.2/units/si/1970/accepted/parsec.md)**
**Definition name:** `parsec`
**Unit name:** parsec
**Latin symbol:** pc
**Display symbol:** pc
**Description:** The distance at which 1 astronomical unit subtends an angle of 1 arcsecond using the definition of the astronomical unit and arcsecond appearing in the International System of Units (SI), 1st ed. (1970)
The parsec unit appears in the International System of Units (SI), 1st ed. (1970) defined in a footnote as "1 parsec is the distance at which 1 astronomical unit subtends an angle of 1 arcsecond; therefore, approximately, 1 pc = 206 265 AU = 30 857 x 10¹² m."
- The International System of Units (SI), 1st ed. (1970) categorizes the unit as "Units for use with the SI in specific domains."
- The International System of Units (SI), 2nd ed. (1973) categorizes the unit as "Non-SI units accepted for use with the International System, whose values in SI units are obtained experimentally."
- The International System of Units (SI), 4th ed. (1981) and later editions omit the unit.
**Resources:**
- [Definition in the International System of Units (SI), 1st Edition](https://www.bipm.org/en/publications/si-brochure)
- [Wikipedia article describing the unit](https://en.wikipedia.org/wiki/Parsec)
**Formats:** [[JSON](parsec.json)] [[MD](parsec.md)]
**JSON definition:**
``` json
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/1970/accepted/parsec",
"$schema": "https://schemas.optimade.org/meta/v1.2/optimade/physical_unit_definition.json",
"title": "parsec",
"symbol": "pc",
"display-symbol": "pc",
"description": "The distance at which 1 astronomical unit subtends an angle of 1 arcsecond using the definition of the astronomical unit and arcsecond appearing in the International System of Units (SI), 1st ed. (1970)\n\nThe parsec unit appears in the International System of Units (SI), 1st ed. (1970) defined in a footnote as \"1 parsec is the distance at which 1 astronomical unit subtends an angle of 1 arcsecond; therefore, approximately, 1 pc = 206 265 AU = 30 857 x 10\u00b9\u00b2 m.\"\n\n- The International System of Units (SI), 1st ed. (1970) categorizes the unit as \"Units for use with the SI in specific domains.\"\n- The International System of Units (SI), 2nd ed. (1973) categorizes the unit as \"Non-SI units accepted for use with the International System, whose values in SI units are obtained experimentally.\"\n- The International System of Units (SI), 4th ed. (1981) and later editions omit the unit.",
"resources": [
{
"relation": "Definition in the International System of Units (SI), 1st Edition",
"resource-id": "https://www.bipm.org/en/publications/si-brochure"
},
{
"relation": "Wikipedia article describing the unit",
"resource-id": "https://en.wikipedia.org/wiki/Parsec"
}
],
"approximate-relations": [
{
"base-units": [
{
"symbol": "m",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/1960/base/metre"
}
],
"scale": {
"value": 3.0857e+16
}
}
],
"x-optimade-definition": {
"label": "parsec_si_1970_accepted",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "parsec"
}
}
```