Re: New Horizons - Question


MadDogR75@xxxxxxxxx wrote:
> In Re: New Horizons - Mission to Pluto
> (link: www.nature.com/news/2006/060116-2.html)
> Vehicle will have 'Long Range Telescope` as part of
> instrument package.
> Sched; jupiter - 2007, Pluto - 2015
>
> It occurs to me that since we will have a high definition,
> low light instrument in place at a known distance,the
> opportunity will exist for some 'hellofa long baseline`
> distance measurement.
> Since many of our distance measurements are hierarchially
> based on the distance of the Cephied variables, (whose
> origional distances were measured by earth orbit parallax),
> doesn't this mission offer an opportunity to improve the
> accuracy of the whole hierarchy of long distance measurement,
> especially as distances are now so signifcant a factor in
> cosmology?
>
> Do we know the location of the vehicle with sufficient
> accuracy at any given time to make the effort worthwhile?
> Would the tasking of the telescope to a few 'star field`
> images overload the mission?
> Is the whole idea flawed in some way?

This isn't a bad idea. But the New Horizons telescope has an
objective mirror of only 8.2 inches, whereas very many instruments have
apertures many times that, giving them resolving powers which probably
make up for the difference in stellar parallax between Earth's &
Pluto's orbits. In fact, the Hipparcus satellite was orbited several
years ago for the single purpose of astrometry with revolutionary
precision. I'm betting that it alone has made cepheid distance
measurements exact enough to be a non-issue.

-Mark Martin

.

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