Double-posting. Ah well..
When calculating distance in Parsecs; SD = ES over Tan1"
For the Sun are we to assume that the distance is a constant and is the distance between the Earth and the Sun?
And could you just explain it in general? Calculating distance is lame...
By definition, an object is one parsec away if it has a parallax of one arc-second.
It turns out that one parsec is about equal to 3.2616 light years.
As for how the distance to the sun is determined, I direct you to the wikipedia page on the astronomical unit.
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