Re: ATM [Fwd: BOUNCE atm@shore.net: Non-member submission from [Scott Marsh <smarsh@geocities.com>]]

[Carl Woebcke <carlw@telis.org>]

Scott,

Motz and Duveen, 30 years ago in "Essentials of Astronomy" said:

"A sidereal day is 23 solar hours 56 solar minutes 4.09 solar seconds,
or 23.934467 solar hours in length.  A sidereal day is defined as the
time interval between two successive transits of the vernal equinox over
the local celestial meridian.  Because of the precession of the
equinoxes, the average sideral day is 1/120th of a second shorter than
the interval between two sucessive transits of a given star across the
observor's meridian.  The difference between the reading on the sidereal
clock at the time of transit of a star and the known right ascension of
this star is the "clock error".  Since the vernal equinox moves
irregularly in its westward precession, the [precise] length of the
sideral day is not constant, but shows slight variation, which is quite
difficult to detect."

Carl Woebcke