Re: If the earth is 6k years old
- From: bill.m.thomas@xxxxxxxxx
- Date: 12 Apr 2007 19:07:06 -0700
On Apr 13, 12:40 pm, "Terry" <kilow...@xxxxxxxxxxx> wrote:
What would be the farthest star we could see?
How far is it to the North star?
The Hipparcos astrometry mission measured 430 +/- 30 ly. It so happens
that this is of particular note, as Polaris is a Cepheid variable
which is accessible to direct parallax measurement. I.e it is one of
the Cepheids used to calibrate the Cepheid distance determination
method. For Cepheids further away than Polaris, the error bars
increase.
By a lucky chance, a star in the LMC was observed to blow up in 1987.
The event called SN 1987A, was the first naked eye visible supernova
seen in nearly four hundred years. It so happens, that the light from
this supernova 're-energized' some gas rings that had been thrown off
from the star quite some time prior to the actual supernova. This
allowed the distance to the LMC to be pegged by the so callled 'light
echo' method namely 167,000 ly. As the LMC contains many Cepheid
variables, this provided an excellent callibration of the Cepheid
distance method. For a discussion of the various methods of measuring
stellar distances, see this article from Ned Wright's cosmology
tutorial:
http://www.astro.ucla.edu/~wright/distance.htm
Bill
.
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