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From: wyatt@cfa.UUCP (Bill Wyatt)
Newsgroups: net.astro
Subject: Re: Re: Question about Sirius
Message-ID: <155@cfa.UUCP>
Date: Mon, 16-Dec-85 12:30:50 EST
Article-I.D.: cfa.155
Posted: Mon Dec 16 12:30:50 1985
Date-Received: Sat, 21-Dec-85 01:18:40 EST
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Organization: Harvard-Smithsonian Center for Astrophysics
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> > >...  Sirius today is visible as a blue-white star
> > >but this article refers to historical accounts that refer to Sirius
> > >as a red star.  The speculation (theory?) presented in the article is
> > >that the white dwarf companion star of the visible blue-white star
> > >was a red giant in the recent past.
> > >
>
> That Sirius B is now less massive than Sirius A is not that unusual;
> ...
> The problem with the Sirius system, to my mind, lies in the assumption
> that something has happened to it in historical times. ...
> ...  Until a detailed study of many historical documents
> from several cultures indicates otherwise (and such a study has not yet
> appeared) I feel justified in saying the burden of proof lies still with the
> historians.
>
> Jeff Brown the Scumbag
> Astronomy Department, U. of Texas, Austin

I completely agree with everything Jeff said, but there may be one
(apparent) way a star changes color - by rising from the horizon.

The ancient Egyptians identified the start of summer as the first time
Sirius was visible rising in the dawn sky. I believe this was near the
summer solstice, and is also where we get the term "dog days" [i.e. hot
summer days. We don't see it that early anymore, because of ~4000
years of precession (Thuban, in Draco was the pole star back then).

The point is that a star on the horizon will be red (and twinkling like
mad), just as the sun reddens at sunrise and sunset. In a
dusty climate, the reddening would also be enhanced. My speculation is
that the reference to Sirius as a red star refers to its appearance just
as it rises, which is when the ancient Egyptians would have been most
interested in it.

Bill Wyatt
--
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