Question

Who invented the word parsec and what does it mean?

Answer 1

Parsec was coined as acronym for 'parallax arcsecond' by British astronomer Herbert Hall Turner in 1913. It is a large unit of distance equal to 648000/`pi` AU.

Explanation:

Parsec is the radius of the circle such that its arc of length 1 AU subtends 1" at the center.

1" = `pi/648000` radian.

Use the formula Arc length = radius X (angle subtended by the arc at the center, in radian measure).

So, 1 parsec = 648000/`pi` AU
1 AU = semi-minor axis of Earth's orbit = Average Earth-Sun distance..
= 149597870.7 km

I think that this definition is a disambiguation-definition, despite that the notion of parallax is not explicit in this definition.