2. The moon is the
earth’s only
natural
satellite.
3. Its revolution period
around the earth is
the same length and
direction as its
rotation period, which
results in the moon
always keeping one
side turned toward
the earth and the
other side turned
away from the earth.
4. The moon has a
noticeable effect on
the earth in the form
of tides, but it also
affects the motion and
orbit of the earth.
5. The sun acts on the
earth and its moon as
one entity with its
center at the
barycenter.
6. The Sun
Because of the elliptical nature of the earth’s orbit and
constant changes in the earth’s rate of spin because of
the previously mentioned phenomena, the sun, as seen
from earth, is moving at a non-uniform rate. This makes
it difficult to use the real position of the sun as a
reference for time keeping. For these purposes, a point
which moves at a constant rate around the earth is used
instead of the real position of the sun. This point is called
the mean sun and is the basis for mean solar time.
