RE: Re: [FH] FTL, astronomy

On Fri, 22 Feb 2002, laserlight@quixnet.net wrote:

> B Lin wrote:
> > 
> > Spectra are unique, they are formed by different amounts of various
elements that produce more of one color when burned  A problem arises
when dust, hydrogen or nebula are in the way as they might absorb parts
of the spectra, reducing the usable parts and making ID more difficult.
> > 
> > You would determine range to a star the same way astronomers
currently do. How do you think they know Alpha Centauri is 4.3 light
years away?
> 
> Parallax ie triangulation. Works well on nearby stars, not so well on
> distant objects.  Actually there are other methods astronomers use on
> more distant stars, about which Indy could probably go on at much
> greater length than I.

There are, I could, but sitting at home trying to type anything
"lengthy" in at 2400bd ain't high on my list of finger exercises
this evening.  ;-)

Trigonometric parallax is good out to about 100 parsecs. After that,
at this time, it falls off rapidly in accuracy (as technology gets
more refined, though, it will slowly expand - when, how, etc I couldn't
begin to tell you ;-). However, it's the most straight-forward of
the various methods used.

Using combinations of spectra and mass/luminosity a rough idea of the
absolute magnitude can be derived, and from the equation I posted
in an earlier message, the distance approximated (you'll note that
for most stars 100 parsecs or further away have round numbers for
their distances; e.g., Betelgeuse is listed as 520 ly as opposed
to, say, 512 or 531 ly).

Other methods involve using special classes of variable stars,
such as RR Lyrae and Cepheid variables. From these extremely
regular variable stars one can use period-luminosity relations
in order to determine distances. These are *generally* used
for determining distances to entire galaxies, rather than
individual stars (since you would only be measuring them, not
other, non-variable, stars).

Okay, I stop here before I get "lengthy".  ;-)	Have a good
evening (or morning, or afternoon, or...)