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(1) Extinction; (2) Mercury



        Matt Wehman writes:

>           I wouldn't go so far as to actually *call*  our avians
>  "terrible lizards". (What is Latin for "terrible bird" anyways?)

        The words (meaning `terrifying lizard') from which `dinosaur' is
derived are Greek, not Latin.  The analogous coinage with the Greek word
for `bird' in place of `lizard' would be `dinornith'.

                                  *  *  *

        A couple of contributors have asserted that the planet Mercury
always has the same face towards the sun.  This is not the case.  According
to the _New Columbia Encyclopedia_,

#           It was long thought that Mercury's period of rotation on its
#  axis was identical to its period of revolution, so that the same side of
#  the planet always faced the sun.  However, radar studies in 1965 showed
#  a period of rotation of about 59 days.  This results in periods of
#  daylight and night of 90 earth days each.

        Before the radar studies, astronomers relied on visual and
photographic evidence collected during the short periods when the angular
distance between Mercury and the sun, as seen from the earth, was as large
as possible and the physical distance between Mercury and the earth as
small as possible.  It so happens that whenever these circumstances
favorable to observation occur together, Mercury is at the same stage in
its rotation, so that whenever astronomers could get a good look at it, it
had the same face towards the sun.  The inductive inference that it was
completely tidally locked turns out, however, to be incorrect.

        There's some complicated kind of tidal effect that supposedly
accounts for the fact that the ratio between Mercury's period of revolution
and its period of rotation is 3:2, but I don't know any of the details.

------  John David Stone - Lecturer in Computer Science and Philosophy  -----
--------------  Manager of the Mathematics Local-Area Network  --------------
--------------  Grinnell College - Grinnell, Iowa 50112 - USA  --------------
----------  stone@math.grin.edu - http://www.math.grin.edu/~stone/  ---------