Re: speed of light

[Ron Ebert <ebert@CITRUS.UCR.EDU>]

At 04:27 PM 10/7/99 -0700, Leigh Palmer wrote:

> > But it's not that easy. "The first real snag comes from the fact that light
> > is not reflected --it's fluorescing," says Gould, and fluorescence takes
> > time to develop, adding a lag that has to be calculated. Worse, the ring is
> > not face-on but tilted, meaning that the secondary bursts of light are
> > further spread out in time because of the varying distances they have to
> > travel from the ring to Earth.
>
> The fluorescence is associated with the interaction of the
> light burst from SN1987A with a ring of material surrounding
> the object rather than with a three dimensional dust cloud
> in the ISM (which would have been ideal).

It seems rings or discs of material are fairly common and three dimensional
clouds of material fairly uncommon. This holds true especially for
planetary nebulae. For supernova explosions and the extreme stellar winds
that form planetary nebulae, there is a propensity for most of the material
to be expelled from the progenitor's equatorial regions and little from its
poles.

> > Although initial estimates were all over the
> > map, several recent calculations, including one by Gould, come up with
> > similar distances to the LMC, about 47 kpc.
>
> That's the smallest distance I've heard quoted.
>
> > The article is about the uncertainty of calibrating the "standard candles"
> > that astronomers use for distance measurements.
>
> I looked for the article but a scan of Science TOCs did not
> find it for me. May I please have the citation? I usually don't
> read Science weekly. I prefer Nature, which points me to the
> Science articles I should read.

Sorry about that. It's in Volume 285, Number 5434 Issue of 10 Sep 1999, pp.
1658 - 1661. I prefer Nature because it is more balanced with better
coverage of physics and astronomy. Science is too heavily biased toward the
biological sciences. But Science's astronomy and physics articles are
usually worthwhile when they run them.


Ron Ebert
ron.ebert@ucr.edu
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                      A SLICE OF PI

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