# on 17-Jun-2018 (Sun)

#### Annotation 3002666192140

The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System

Parsec - Wikipedia
metric (SI) units 7016308570000000000♠3.0857×10 16 m ~31 petametres imperial & US units 7016308575618560000♠1.9174×10 13 mi astronomical units 7016308568047999355♠2.06265×10 5 au 7016308567400801506♠3.26156 ly <span>The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond,  which corresponds to 7005648000000000000♠648000/π astronomical units. One pa

#### Annotation 3002668289292

A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to 7005648000000000000♠ 648 000 / π astronomical units

Parsec - Wikipedia
0♠1.9174×10 13 mi astronomical units 7016308568047999355♠2.06265×10 5 au 7016308567400801506♠3.26156 ly The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. <span>A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond,  which corresponds to 7005648000000000000♠648000/π astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun.

#### Annotation 3002669862156

One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length.

Parsec - Wikipedia
arge distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond,  which corresponds to 7005648000000000000♠648000/π astronomical units. <span>One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun.  Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the

#### Annotation 3002671435020

The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun.

Parsec - Wikipedia
tance at which one astronomical unit subtends an angle of one arcsecond,  which corresponds to 7005648000000000000♠648000/π astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. <span>The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun.  Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun. [citation needed] The parsec unit was probably first suggested in 1913 by the British

#### Annotation 3002673007884

Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun.[ citation needed ]

Parsec - Wikipedia
s to 7005648000000000000♠648000/π astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun.  <span>Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun. [citation needed] The parsec unit was probably first suggested in 1913 by the British astronomer Herbert Hall Turner.  Named as a portmanteau of the parallax of one arcsecond, it was defined so as

#### Annotation 3002675105036

Named as a portmanteau of the parallax of one arcsecond

Parsec - Wikipedia
) from the Sun.  Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun. [citation needed] The parsec unit was probably first suggested in 1913 by the British astronomer Herbert Hall Turner.  <span>Named as a portmanteau of the parallax of one arcsecond, it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data. Partly for this reason, it is the unit prefer

#### Annotation 3002676677900

it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data.

Parsec - Wikipedia
ided eye in the night sky are within 500 parsecs of the Sun. [citation needed] The parsec unit was probably first suggested in 1913 by the British astronomer Herbert Hall Turner.  Named as a portmanteau of the parallax of one arcsecond, <span>it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data. Partly for this reason, it is the unit preferred in astronomy and astrophysics, though the light-year remains prominent in popular science texts and common usage. Although parsecs are u

#### Annotation 3002678250764

The parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun.

Parsec - Wikipedia
r distances were undertaken by German astronomer Friedrich Wilhelm Bessel in 1838, who used this approach to calculate the 3.5-parsec distance of 61 Cygni.  [imagelink] [emptylink] stellar parallax motion from annual parallax <span>The parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun. Equivalently, it is the subtended angle, from that star's perspective, of the semimajor axis of the Earth's orbit. The star, the Sun and the Earth form the corners of an imaginary right

#### Annotation 3002679823628

Equivalently, it is the subtended angle, from that star's perspective, of the semimajor axis of the Earth's orbit. The star, the Sun and the Earth form the corners of an imaginary right triangle in space: the right angle is the corner at the Sun, and the corner at the star is the parallax angle. The length of the opposite side to the parallax angle is the distance from the Earth to the Sun (defined as one astronomical unit (au), and the length of the adjacent side gives the distance from the sun to the star. Therefore, given a measurement of the parallax angle, along with the rules of trigonometry, the distance from the Sun to the star can be found. A parsec is defined as the length of the side adjacent to the vertex occupied by a star whose parallax angle is one arcsecond.

Parsec - Wikipedia
ni.  [imagelink] [emptylink] stellar parallax motion from annual parallax The parallax of a star is defined as half of the angular distance that a star appears to move relative to the celestial sphere as Earth orbits the Sun. <span>Equivalently, it is the subtended angle, from that star's perspective, of the semimajor axis of the Earth's orbit. The star, the Sun and the Earth form the corners of an imaginary right triangle in space: the right angle is the corner at the Sun, and the corner at the star is the parallax angle. The length of the opposite side to the parallax angle is the distance from the Earth to the Sun (defined as one astronomical unit (au), and the length of the adjacent side gives the distance from the sun to the star. Therefore, given a measurement of the parallax angle, along with the rules of trigonometry, the distance from the Sun to the star can be found. A parsec is defined as the length of the side adjacent to the vertex occupied by a star whose parallax angle is one arcsecond. The use of the parsec as a unit of distance follows naturally from Bessel's method, because the distance in parsecs can be computed simply as the reciprocal of the parallax angle in a

#### Annotation 3002681396492

The distance in parsecs can be computed simply as the reciprocal of the parallax angle in arcseconds (i.e. if the parallax angle is 1 arcsecond, the object is 1 pc from the Sun; if the parallax angle is 0.5 arcseconds, the object is 2 pc away; etc.).

Parsec - Wikipedia
he star can be found. A parsec is defined as the length of the side adjacent to the vertex occupied by a star whose parallax angle is one arcsecond. The use of the parsec as a unit of distance follows naturally from Bessel's method, because <span>the distance in parsecs can be computed simply as the reciprocal of the parallax angle in arcseconds (i.e. if the parallax angle is 1 arcsecond, the object is 1 pc from the Sun; if the parallax angle is 0.5 arcseconds, the object is 2 pc away; etc.). No trigonometric functions are required in this relationship because the very small angles involved mean that the approximate solution of the skinny triangle can be applied. Though it

#has-images

### Calculating the value of a parsec [ edit ] [imagelink]

In the diagram above (not to scale), S represents the Sun, and E the Earth at one point in its orbit. Thus the distance ES is one astronomical unit (au). The angle SDE is one arcsecond ( 1 / 3600 of a degree) so by definition D is a point in space at a distance of one parsec from the Sun. Through trigonometry, the distance SD is calculated as follows:

$$\mathrm {SD} ={\frac {\mathrm {ES} }{\tan 1''}}$$ $$\mathrm {SD} \approx {\frac {\mathrm {ES} }{1''}}={\frac {1\,{\mbox{au}}}{{\frac {1}{60\times 60}}\times {\frac {\pi }{180}}}}={\frac {648\,000}{\pi }}\,{\mbox{au}}\approx 206\,264.81{\mbox{ au}}.$$

Parsec - Wikipedia
ssed his concern for the need of a name for that unit of distance. He proposed the name astron, but mentioned that Carl Charlier had suggested siriometer and Herbert Hall Turner had proposed parsec.  It was Turner's proposal that stuck. <span>Calculating the value of a parsec [imagelink] In the diagram above (not to scale), S represents the Sun, and E the Earth at one point in its orbit. Thus the distance ES is one astronomical unit (au). The angle SDE is one arcsecond (1/3600 of a degree) so by definition D is a point in space at a distance of one parsec from the Sun. Through trigonometry, the distance SD is calculated as follows: S D = E S tan ⁡ 1 ″ {\displaystyle \mathrm {SD} ={\frac {\mathrm {ES} }{\tan 1''}}} S D ≈ E S 1 ″ = 1 au 1 60 × 60 × π 180 = 648 000 π au ≈ 206 264.81 au . {\displaystyle \mathrm {SD} \approx {\frac {\mathrm {ES} }{1''}}={\frac {1\,{\mbox{au}}}{{\frac {1}{60\times 60}}\times {\frac {\pi }{180}}}}={\frac {648\,000}{\pi }}\,{\mbox{au}}\approx 206\,264.81{\mbox{ au}}.} Because the astronomical unit is defined to be 7011149597870700000♠149597870700 m,  the following can be calculated: Therefore, 1 parsec ≈ 7005206264806247096♠206264.8062470

#### Annotation 3002686901516

The astronomical unit is defined to be 149 597 870 700 m ,

Parsec - Wikipedia
{\displaystyle \mathrm {SD} \approx {\frac {\mathrm {ES} }{1''}}={\frac {1\,{\mbox{au}}}{{\frac {1}{60\times 60}}\times {\frac {\pi }{180}}}}={\frac {648\,000}{\pi }}\,{\mbox{au}}\approx 206\,264.81{\mbox{ au}}.} Because <span>the astronomical unit is defined to be 7011149597870700000♠149597870700 m,  the following can be calculated: Therefore, 1 parsec ≈ 7005206264806247096♠206264.806247096 astronomical units ≈ 7016308567758100000♠3.085677581×10 16 metres ≈ 7001191735115770000♠1

#### Annotation 3002689260812

A corollary states that a parsec is also the distance from which a disc one astronomical unit in diameter must be viewed for it to have an angular diameter of one arcsecond (by placing the observer at D and a diameter of the disc on ES).