Question

What is the difference between a radian, an arcsecond and a parsec?

Answer 1

I define all three terms below.!

Explanation:

A radian is a measure of an angle. If you imagine a line from the centre of a circle out to its circumference, then sweep that line until the point on the circumference moves a distance (along an arc) that is equal to the radius to the circle, the angle swept out this way is called a radian. It is equal to `360/(2pi)=57.3°`

An arc-second is an angle that is equal to `1/3600` of a degree. (Or, in other words, an arc-minute is `1/60`th of a degree and an arc-second is `1/60`th of an arc-minute.)

A parsec is a distance. In particular, it is equal to the distance an object like a star would have to be from an observer on Earth so that two observers, separated by one astronomical unit (the mean distance from the Earth to the Sun) would observe one arc-second of difference as they tried to point their telescopes at the star.

That said, a parsec is equal to 206 265 astronomical units, or 3.26 light years.

Answer 2

`darrdarrdarr`

Explanation:

Radian

Its the length of an arc of circle whose measure is equal to the radius of the circle.

https://www.youtube.com/watch?time_continue=163&v=EnwWxMZVBeg

Arcsecond
`1 " degree "= 1° = 1/360 "of a circle"`

`1 " arcminute" = 1' = 1/60 "of a degree"`

`1 " arcsecond" = 1'' = 1/60 "of an arcminute" = 1/(60xx60)=1/3600 "of a degree"`

For a rough estimate, on a clear sky, go out and see the full moon. It should cover about `1/2` of a degree in the sky, which is equal to `3600/2=1800 "arcseconds"`

Parsec

It comes from two words : `color(red)"par""allax"` and `"arc"color(red)"sec""ond"`.

You can see parallax effect by holding your hand in front of your eyes and alternatingly closing each eye. Your hand appears to move relative to the background.

So, a parsecond is the parallax of `1` arcsecond .

`"Distance in parsecs[pc]"=1/"Parallax angle in arc seconds"`