# Error propagation of distance modulus and parallax

• June 17th, 2011, 05:01 PM
muse19
Error propagation of distance modulus and parallax
Hi!

Here is my problem: there is a star, for which we know the distance, d=21.2 pc,
the measurement error is delta_d=1.8 pc. The question is that how far should we put this star,
so that the following equation would be true: d/delta_d = 3?
The teacher told me to use two formulas: m-M=-5+5log(d) and pi=1/d (pi=parallax),
and then do some error propagation calculations.
Of course, I have already tried it using the equations above,
but I did not succeed.
Does anybody have any idea?
Actually, it would be OK as well, if anybody could do it using
any other equations.
Thank you, and sorry for my english.

Cheers, Joe
• July 10th, 2011, 03:21 PM
Michael_Roberts
This seems like quite an easy question on the surface, but some assumptions have not been given.

Are we assuming that the error measurement in the distance increases for increasing distances...if so, what is the relationship?