Astronomers measure mass of largest dwarf planet

[Melkane]

HubbleSite - NewsCenter - Astronomers Measure Mass of Largest Dwarf Planet (06/14/2007) - The Full Story

Melkane Reviewed by Melkane on 06-17-2007. Astronomers measure mass of largest dwarf planet HubbleSite - NewsCenter - Astronomers Measure Mass of Largest Dwarf Planet (06/14/2007) - The Full Story Rating: 5

[Divadish]

How far away from us is this ?

[Staurm]

I was wondering why they had to calculate its mass the same way they do with binary stars. I'm guessing it's because they don't yet know the orbital period P, or the semi-major axis, a. a is the distance between the two farthest most points on the orbital path, which is usually elliptical. They haven't said how far it is, and to the best of knowledge I think there is no way to calculate its distance from the sun until they can measure or estimate P using Keplers third law, and lets face it it could be hundreds of years long. I don't know if they can measure velocity from red shift using Hubble's Law accurately enough to calculate the period based on this, it probably never travels towards or away from the earth fast enough to give rise to a detectable red or blue shift.

Kepler's laws of planetary motion - Wikipedia, the free encyclopedia
Hubble's law - Wikipedia, the free encyclopedia

EDIT I score a C in my astronomy resits, d'oh. Here are the hard facts, I can't work out how they measured the distance yet though...

HubbleSite - NewsCenter - Astronomers Measure Mass of Largest Dwarf Planet (06/14/2007) - Fast Facts

[Staurm]

Wait... I know how. Of course. If they record its position in the sky over the course of a year, it will make a sinusoidal pattern against the distant background. In the same way as if you watch a bullet flying past you in a straight line and you jump up and down, if you could do that. Because we know how far away the sun is, through simple trigonometry the distance can be calculated very easily. It's the same method used to calculate the distance of the nearest stars, after that they start to use Hubble red shift law, and some other crazy shit. I still think its pretty difficult to measure P from the data they have since its distance to the earth is not the same as its MEAN distance to the sun.