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From: msb@lsuc.UUCP (Mark Brader)
Newsgroups: net.astro,net.space
Subject: Was Sirius red after all?
Message-ID: <1146@lsuc.UUCP>
Date: Sun, 9-Mar-86 22:29:15 EST
Article-I.D.: lsuc.1146
Posted: Sun Mar  9 22:29:15 1986
Date-Received: Sun, 9-Mar-86 23:30:16 EST
References: <8603020306.AA00249@s1-b.arpa> <8603061510.AA04282@infinet.UUCP>
Reply-To: msb@lsuc.UUCP (Mark Brader)
Organization: Law Society of Upper Canada, Toronto
Lines: 77
Xref: utcs net.astro:1453 net.space:5732
Summary: New evidence

Pardon the long inclusions here, but I'm adding a group to this...

Robert Elton Maas wrote the following as a tangent to another
topic being discussed in net.space (and the corresponding ARPA
mailing list, whatever it's called):

> > By the way, in latest Sky&Telescope there's a note on Sirius being
> > reddish in recorded history (in fact about 600 AD), because at that
> > time its white-dwarf companion was in the red giant stage. It's hard
> > to believe the conversion from red giant to white dwarf could occur so
> > quickly, although with Sirius gobbling most of the loose hydrogen as
> > fast as it is shed, and ionizing & light-pressure-shoving the rest of
> > the emitted hydrogen, I could imagine it within the realm of
> > possibility. Any news since S&T publishing date on that topic that you
> > know of?

Jim Barnes replied:

> I recently (two months ago?) read an article in the Boston Globe
> that said roughly the same thing - Sirius was reddish within recorded
> history.  I posted the same question to net.astro.  The general response
> received was that the redness was due to the time of day when the
> observations were made.  i.e. Sirius sets near the sun during the dog
> days of the summer, hence the reddish color is due to the sunset, not
> the color of the star.  Current theories of stellar evolution do not
> allow for a star to evolve that rapidly.

Well, as one of the people who replied to Jim's previous query in
net.astro, I feel obliged to correct myself.  See, this hypothesis
about Sirius being red has been proposed and put down before, and I
quoted an article a few years old.  (I also said, "Why is this in
the Boston Globe now?", and no one replied.)

The reason it was in the Boston Globe is that there's new evidence.
I don't read Sky & Telescope, but it was in Scientific American in
February.  (Page 59, in the "Science and the Citizen" column).
They quoted a letter in Nature, but did not mention which issue;
presumably the S&T article refers to the same letter.

I will now summarize the Scientific American item in my own words.
(The only reason I didn't do this sooner, by the way, was that I was
sure someone else would cite it!)

   Ancient Babylonian, Greek, and Roman texts were known to consistently
   refer to Sirius as red.  But now there is medieval evidence for this as
   well.  Wolfhard Schlosser and Werner Bergmann of the Ruhr University
   (Bochum, W. Germany) studied an astronomical almanac that was compiled
   by Gregory of Tours about 580 AD.  Only one copy exists.  The almanac
   was written to help monasteries to find the time at night, so it give
   month-by-month lists of rising times for various constellations.
   
   Schlosser and Bergmann examined representations of the 6th century sky
   at a planetarium.  Gregory refers to a star Rubeola or Robeola, which
   had been thought to be Arcturus; but this is impossible and it must
   actually have been Sirius.  But the name means red or rusty.
   The latter to Nature suggested that the explanation is that Sirius B
   was a red giant that recently.
   
   The transition from red giant to white dwarf is supposed to take very
   much longer than 1,500 years, and is generally accompanied by cataclysmic
   explosions.  It is conceivable that the slightly elevated level of metals
   in Sirius A reflects an explosion in Sirius B, though unobserved, but
   the apparent speed of the transition is unexplained.

One thought occurs to me.  The previous explanation could still be
correct, i.e., that Sirius was important to the ancient Egyptians only when
it was rising (when any star appears red), and that the Greek and
Roman references to color are metaphorical.  See, I figure it could
be that the Egyptians started a tradition of calling Sirius reddish,
and that this tradition led to the Greek and Roman metaphorical
references, and that they in turn led to the name Rubeola, and during
all that time nobody cared to look at the actual color of the star.
(How old is the Latin-sounding name Sirius anyway?)

Personally, I find both possibilities hard to believe.  Isn't science fun?

Mark Brader