The sun and the moon-On one orbit

Motion of the Sun,the moon and other stars
and plants have always been considered as
one of the natures most important phenomena.
The study of such movements has gradually
led to the recognition of a larger world
and,man through such studies,has discovered
many of the mystries of the universe.

Following the discovery of the fact by
Galileo that earth rotates around the Sun,
scientists started extensive studies to
discover how stars and planets move around
in the cosmos.As an example,Copernicus showed
that the Sun is the focal point of movement
of the Earth and planets however,assuming
their courses to be circular,he couldn't
fully explain their orbits.In 17th century
Kepler,an Austrian scientist,considering
the movement of planets , proposed three
general laws in this regard.In the first of
his laws,which is the most important one of
all, he said that each planet rotates on
an elliptical orbit round the Sun in such
a way that the Sun is always in one of its
foci.Newton's general law of gravitation
states that any particle of matter in the
universe attracts other particles with
a force,the amount of which is in direct
relation with masses of these two particles
and a converse relation to their distance
squared.This considerably helped to state
and explain the general motions of planets
and stars.With regard to Newton's law,whithin
the solar system,the Sun,the Earth and each
of its planets exert gravitational effects on
each other and since the Sun is the largest
body of this system,its gravitational force
exerted on any planet is dominant and hence
all the planets are attracted toward the Sun.
This force plays a basic role in revolution
of planets.It's worth mentioning that the Sun
itself is not an exception to this general
rule.

The Sun is rotating on an approximately
elliptical orbit and at a speed of about
25 km/s around the center of milky way
galaxy.In other words regarding the distance
between the Sun and the center of galaxy,
this brilliant star rotates once every 042
million years around the milky way galaxy.
Moreover,the Sun rotates around its axis,
from the east to the west.This revolution
however,has a significant difference with the
motion of other planets and that the Sun,due
to its very high temperature,is a globe
consisting of therefore,all its parts do
not move together as a solid mass but its
equatorial regions with a velocity of
7250 km/h every 25.5 day and its polar
regions every 34.5 days rotate oround
its axis.

Moon,the only natural planet of the Earth,
according to the rules governing the motion
of planets and stars is rotating on
an elliptical orbit around the Earth,while
the Earth is always situated in one of its
foci,therefore its distance from the Earth
is not perpetually equal.On its elliptical
orbit,the nearest and farthest distance of
the moon from the Earth is 353600 km and
404800 km respectively.The moon travels its
revolution around the Earth with a velocity
of 1000 m/s in a period of 27 days,7 hours,
43 minutes and 11.5 seconds.Of course with
regard to gravitational forces of the Sun
and to some extent other stars , some
irregularities are seen in the elliptical
orbit of the moon.The revolution of the moon
around itself rotation has a special
specification i.e.the duration of one
revolution of moon around the Earth equals
to that of its rotation.The result of such
a phenomenon is that in the course of these
two motions,always one half of the moon faces
toward the Earth . Among factors causing
oscillations in the moon's movements are
the change in the speed at which moon is
revolving around the Earth,the deviation in
the axis of the moon in relation to its
orbit,the gravitational force of the Sun
and other planets especially Venus and Mars.
Some astronomers believe that the moon during
its continuons revolution and rotation
gradually approaches the Earth and as the
case may be,one day it may become so close
to the Earth that owing to the gravitational
force of the Earth and the intensity of the
centrifugal force caused by its circular
motion,will eventually be smashed.