1. Established Member
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Feb 2004
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## Parallax Equations

While reading my introductory astronomy textbook, I read about two formulae that were used to determine distances using parallax.

One was d(parsecs)=1/p(parallax in arc seconds), but I vaguely remember something like:

distance=baseline*(parallax in degrees/57.3)

What is this second formula and when is it used/is it the same as the 1st, but written in a different form?

Thanks!

2. Established Member
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Mar 2005
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1,234
The Parsec is a unit invented just for parallax.

Theta = a/d

a is in AU. d is the distance in parsecs. Theta is in arcseconds.

Theta = a/d also works if a and d are in the same units. But then Theta is in radians.

3. Originally Posted by Brady Yoon
distance=baseline*(parallax in degrees/57.3)

What is this second formula and when is it used/is it the same as the 1st, but written in a different form?
Note this second formula must be wrong, as it has parallax increasing with distance, which of course can't be right. Stick to tony87304's forms.

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