Re: Curious about Sirius

Eric Kellar notes:

>>The direct cotton dye sirius red F3B and others like it were originally 
named [after the star Sirius] to denote the brightness of the red color.<<

But Sirius isn't red - it's a very hot blue star. And thereby hangs a curious 
tale. Most astronomical texts from the ancient world refer to Sirius as being 
red ("hypokirrhos"), the last such reference being about 600 C.E. (This topic 
was done to death several years ago in Astronomy and in Sky and Telescope.)

There was a lot of speculation that the star had changed its color since 
ancient times, even though this was astronomiclaly most implausible.

Apparently the red color occurs when Sirius is near the horizon - just like 
the Sun appears red at its rising and setting. You can see this phenomenon 
more easily with Venus, but apparently Sirius is the only star that is bright 
enough to register as red to human eyes when it's near the horizon.

Presumably the Procion reactive cotton dyes are named after nearby Procyon, 
the other "dog star".

Guess it sounded better than "Betelgeuse Red".

Bob Richmond
Samurai Pathologist
Knoxville TN

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