FIRTH@TL-20B.ARPA (03/11/86)
[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
-------Lynn.ES@XEROX.COM (03/12/86)
Why don't people go out and look at Sirius instead of arguing in a vacuum? It turns out I often do (I mean look; the fact that I often argue is not the point :-), not to prove the "Red Sirius" theory, but because I like the stars. Sirius almost always looks blue-white to me, but it has on occasion looked as red as a stop light. It has also looked quite green, in fact within minutes of looking red. These funny colors occurred when Sirius was low in the sky and the air was fairly turbulent. While I must commend Firth for looking rather than blindly arguing, his observation of Venus instead of Sirius is probably irrelevant, because the finite size of planets (roughly a minute of arc for Venus) makes them behave differently than stars with regard to atmospheric effects; for example, planets twinkle decidedly less than stars. After seeing Sirius quite red from atmospheric effects, I have to believe it simply got into the literature as red from such a viewing, and has been perpetuated in print. /Don Lynn
carroll@uiucdcsb.CS.UIUC.EDU (03/15/86)
Looking at the stars from "Deep in the heart of Texas", in and around Big Bend national park (where there is not much light polution), my brothers and I observed 3 stars, all within about 30 degrees of the horizon, all blinking red, blue and white. This effect was so pronounced that it was only after a hour or more of observation that we decided they were stars nd not airplanes. Checking my star maps (and if I remember correctly), the stars were Sirius, Procyon, and Mirzam. Any one else ever seen this?
cramer@kontron.UUCP (Clayton Cramer) (03/18/86)
> Why don't people go out and look at Sirius instead of arguing in a > vacuum? It turns out I often do (I mean look; the fact that I often > argue is not the point :-), not to prove the "Red Sirius" theory, but > because I like the stars. Sirius almost always looks blue-white to me, > but it has on occasion looked as red as a stop light. It has also > looked quite green, in fact within minutes of looking red. These funny > colors occurred when Sirius was low in the sky and the air was fairly > turbulent. > > While I must commend Firth for looking rather than blindly arguing, his > observation of Venus instead of Sirius is probably irrelevant, because > the finite size of planets (roughly a minute of arc for Venus) makes > them behave differently than stars with regard to atmospheric effects; > for example, planets twinkle decidedly less than stars. > > After seeing Sirius quite red from atmospheric effects, I have to > believe it simply got into the literature as red from such a viewing, > and has been perpetuated in print. > > /Don Lynn But the ancients were quite knowledgeable naked eye astronomers. They would know that Sirius was, when low to the horizon, occasionally red and other colors, for short periods of time. Hard to believe that they would call it "red" unless it was so quite consistently. Also, the color distortions are because Sirius is low in the sky when viewed from northern latitudes. In the latitude of Egypt, it isn't low in the sky.