On Mar 28, 12:02*pm, Ben wrote:
http://en.wikipedia.org/wiki/Moon : "Libration also changes the angle
from which the Moon is seen, allowing about 59% of its surface to be
seen from the Earth".

I don't know whether that figure, dominantly at least due to apparent
"side to side" motion caused by eccentricity, includes the apparent
"nodding" motion due to tilts, or the extra half a degree all round due
to parallax and the size of the Earth.

There are three classes of libration, optical, physical and
topocentric. *Jean Meuss in 'Astronomical Algorithms'
states:
* * * * However, apparent oscillations known as *optical librations*
which are due
* * * * to variations in the geometric position of the
Earth.......allow about 59%
* * * * of the surface to be observed from the Earth. (p.371)

He goes on to say that *physical libration* can never be larger than
0.04 degree in both latitude and longitude.
Well that's not very much and would be observable only under the most
rigorous conditions.

But concerning *topocentric librations* he states that the geocentric
values of the librations and the position angle
of axis should be reduced to the values at the place of the observer
on the surface of the Earth. *"For the librations
the values may reach 1 degree and have important effects on limb
contour."

So by shifting one's position around the Earth, say from Hudson Bay to
Tierra del Fuego one could see perhaps
60% of the Moon's surface? * I don't know. *I've always held the 59%
factor as an adequate estimate.

The moon does not rotate hence librations,and I haven't even given it
consideration yet are products of the moon's orbital circuit of the
Earth and the Earth's orbital circuit of the Sun.You can't even begin
to consider lunar behavior without first considering the Earth's
orbital characteristic and specifically the single orbital daylight/
darkness cycle arising solely from the slow and uneven turning of the
Earth to the central Sun about a traveling axis stretching through the
center of the Earth from Arctic to Antarctic circles.

Sorry that none of you appear to have the talent to consider the
physical considerations involved in the observation,considering that
your minds are rotted by the 'no center/no circumference' ideology I
wouldn't hold my breath waiting for an interpretation of lunar and
planetary motion which generates the libration observation,no harm
trying like Isaac did but 'lunar rotation'!,my astronomical ancestors
wouldn't believe people would ever conclude such drivel.