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From: FIRTH@TL-20B.ARPA
Newsgroups: net.space
Subject: Red Sirius?
Message-ID: <8603111652.AA09647@s1-b.arpa>
Date: Tue, 11-Mar-86 10:37:58 EST
Article-I.D.: s1-b.8603111652.AA09647
Posted: Tue Mar 11 10:37:58 1986
Date-Received: Fri, 14-Mar-86 03:34:59 EST
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[sounds like a character from an S&S tale!]

Just thought I'd make a few points

(1) Why did the ancients refer to Sirius as "red"?  The obvious reason
    is that it WAS red, but unfortunately that cannot be relied on.  The
    debate on how the Greeks and Romans saw colours is an old one, and
    there are no good conclusions.  For example, there are several
    examples of Greek sculpture with unnatural colours - green horses
    on the Parthenon freize is one - and we don't believe in green horses.
    As another example, what about Homer's "wine-dark sea"?  I've sailed
    over that same sea, and it isn't wine coloured (nor particularly
    dark).  Moving up to the Arabs, the books say that they called Egypt
    "the black land" because of the colour of the soil - but the soil of
    Egypt isn't black; it's reddish-brown.

(2) Sirius seems red close to the horizon?  It didn't last night, when
    I looked.  To be fair, I can't recall observing Sirius close to its
    heliacal rising, ie near the Sun, but I've often seen Venus in that
    position, and IT never looked red.  The Mesopotamians observed that
    planet for centuries, and if it ever looked red to them, they didn't
    say so.

(3) Sirius looked red because its companion was a red giant?  I doubt it.
    Check the difference in intrinsic magnitude between a red giant and
    a main-sequence blue-white star - the former would be drowned out.  

(4) I endorse the idea that the mediaeval guys might have simply copied
    the alleged fact of Sirius' redness without bothering to look.  After
    all, they copied a lot of other errors that simple observation would
    have shown to be wrong; the most notorious example perhaps being
    Aristotle's assertion that heavier things fall faster.  But that can't
    explain where the notion came from in the first place.

Another trivial pursuit in the history of science...!

Robert Firth
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