Hipparcos Limit ?

[dannat]

Does anyone know the limit-ing distance of the hipparcos detection.. ie can it detect out to 100 parsecs/100 LY.

[renormalised]

100pc or 100ly....all too easy.

Go here... HIPPARCOS (http://en.wikipedia.org/wiki/Hipparcos)

[Robh]

I'm not sure what your question actually is. The Hipparcos mission measured star positions, distances, parallaxes and proper motions. It would certainly have measurements for the star Antares which is about 600 ly distance and Deneb which is 3000 ly distance. The limitations on measurement were more to do with visual magnitude e.g. the Hipparcos catalogue lists some 118000 stars to visual magnitude 13 but is only complete to magnitude 7.3.

Regards, Rob

[Robh]

After thought ...
If your talking about the distance of a star at the limit that Hipparcos can measure parallax (precision 1 milliarcsecond at best) then this corresponds to a distance of 1/0.001=1000 pc or roughly 3260 ly.

Regards, Rob.

[Coen]

There are at least two limits
- visual magnitude that could be measured
- positional accuracy that could be measured

The positional accuracy eventually was on the order of 0.001 arc sec (or 2.78x10^(-7) degree) so from that you could naively work out that the distance that could be determined. (Measure at time A, subtract measure at time B occurring 6 months later, best measurement difference able to be measured is 0.001 arc sec)

Naively: If I recall my simple trig correctly, for the purposes of first order feel gives: tan(2.78x10(-7)) = 1(AU)/h where h is the distance of the object in kilometres and 1(AU) is the earth sun distance which is your maximum baseline. So with everything working in your favour you could get out to about 2.061x10^(8) AU or 3260 light year.

In reality you have plenty of other factors involved including how the data is taken and you also are measuring against a moving background not an absolute one. Further the satellite was after accurate positional measurements of the stars first. So all this means is that the actual figure is out to around 1600 light years.

Whether or not all stars within that volume were bright enough to be accurately measured and were part of the observing programme is the completeness question.

There were also other confounding factors such as whether the stars are double or multiple.

There is a satellite programme due to go into orbit (Gaia: http://en.wikipedia.org/wiki/Gaia_mission) which will seek to accurately measure a huge number of stars and then solve the very big inverse problem i.e. solve all positions at the same time due to the various inter-relationships. Good fun debugging that code. The target is to get out to greater than 10,000 light years.

[dannat]

thanks for the replies -its for an astro physics Q on a VCE paper
daneil