Re: Reconsidering Halton Arp

In article <[EMAIL PROTECTED]>,
Randy Poe <[EMAIL PROTECTED]> wrote:
>[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.

I vaguely recall main sequence charts.  What could be considered a problem 
for distance determination is that some things are big and red, big and 
white, small and red, small and white  So there's some more theory 
involved in turning brightness and temperature into a distance.  I thought 
having a diameter measurement must be more direct.

-- 
"When the fool walks through the street, in his lack of understanding he 
calls everything foolish." -- Ecclesiastes 10:3, New American Bible