Re: Reconsidering Halton Arp

[EMAIL PROTECTED] (Gregory L. Hansen) wrote in message news:<[EMAIL PROTECTED]>...
> In article <[EMAIL PROTECTED]>,
> Randy Poe  <[EMAIL PROTECTED]> wrote:
> >On Sun, 30 Nov 2003 11:13:10 -0800, "greywolf42"
> ><[EMAIL PROTECTED]> wrote:
>  
> >Explain to me how Leavitt managed to use Big Bang theory for her
> >calibration in 1912, and what "use Big Bang for calibration" means,
> >and I'll explain both Leavitt's calibration and the Cepheid variable
> >method.
> 
> In Fowles' book on optics I read about Michelson's stellar interferometer, 
> which measures stellar diameters.  And there was an intensity method 
> that's supposed to have improved precision, but I don't really understand 
> it.  Fowles didn't give any numbers, but it seemed to me that when 
> parallax fails, you can keep going if you can measure diameter, 
> and combine that with brightness and temperature.  Assuming diameter 
> measurements can be made farther out than parallax measurements.

What I found in reading pages on astronomical distance
estimation is that many authors seem to use a technique
called "main sequence fitting". Google on that term and
you'll learn more than you ever wanted to.

The original idea is to use the brightness: based on other
data about the source, how bright should it be, and then
how bright does it actually appear to be. The difference
tells you distance in a more or less obvious way.

This idea has been modernized. Now rather than brightness
it's some sort of multi-spectral measure that gives much
more accurate determinations. But it's still the same
basic idea: if you know how bright something is, and you
see how bright it appears to be, then you know how far
away it is. No Big Bang assumptions. The big unknown
always is "how bright is this object really?" and that's
where main sequence fitting comes in.

I'm probably mangling this a little. I need to read those
pages in more detail before responding directly to
greywolf.

             - Randy