SDSS and HR Diagrams?

Question

Hey I'm supposed to be doing this exercise for my physics class and I was collecting information to make a HR diagram, but when I was collecting the trigonometric parallaxes, some of them are negative, and that makes the distance you work out from it to be negative also.

Does anyone know what I am supposed to do? I emailed the website and they just replied "what do you THINK it means" ...yeah alot of help there...

anyway, thank you to anyone who can help

Answer 1

I don't understand why you would be getting any negative values.  None of the trig functions used in parallax measurement will yield a negative number.

Second, I don't understand why you are looking at distances anyway.  The two factors considered in the H-R diagram are spectral classification, (temperature), and luminosity.  These should be given.  I can't help you more, without more detail about what you're trying to do.

Answer 2

Here's a possibility.  You take an image of a star, and some six months later you take another.  The Earth has moved nearly 200 million miles.  So you use that as the baseline.

But the Sun and the Earth have moved also. And the target star has moved. You really must wait another six months and take at least another image.

What i want are two space telescopes, to take simultaneous images.  There'd still be aberration, but you have that anyway, and besides, it's pretty well understood.

Brant - you need distance to compute absolute luminosity.