2. A rotation is a circular movement of an object
around a center (or point) of rotation. A
three-dimensional object always rotates around an
imaginary line called a rotation axis. If the axis passes
through the body's center of mass, the body is said to
rotate upon itself, or spin.
3. The primary effect of Earth's rotation is the
phenomenon of day and night. The rotation of the
Earth about its axis in an anticlockwise direction
gives us the impression that the sun rises in the east
and sets in the west.
4. In astronomy, the Earth's orbit is the motion of the
Earth around the Sun, from an average distance of
149.59787 million kilometers (93 million miles) away.
A complete orbit of the Earth around the Sun occurs
every 365.256363004 mean solar days (1 sidereal year
).
5. The Earth's axis is tilted at an angle of 23.5 degrees.
This means that the Earth is always "pointing" to one
side as it goes around the Sun. So, sometimes the Sun
is in the direction that the Earth is pointing, but not
at other times. The varying amounts of sunlight
around the Earth during the year, creates the
seasons.
6. A solstice is an astronomical event that occurs twice
each year as the Sun reaches its highest or lowest
excursion relative to the celestial equator on the
celestial sphere. The solstices, together with the
equinoxes, are connected with the seasons.
7. The summer solstice occurs when the tilt of a
planet's semi-axis, in either the northern or the
southern hemisphere, is most inclined toward the
star (sun) that it orbits. Earth's maximum axial tilt
toward the sun is 23° 26'. This happens twice each
year, at which times the sun reaches its highest
position in the sky as seen from the north or the
south pole.
8. Winter solstice is an astronomical phenomenon
which for the Northern Hemisphere occurs in
December and which for the Southern Hemisphere
occurs in June.
For the Northern Hemisphere, the moment of winter
solstice is when the sun's elevation with respect to
the North Pole is at its most negative value since the
previous December.
9. An equinox occurs twice a year, around 20 March
and 22 September. The word itself has several related
definitions. The oldest meaning is the day
when daytime and night are of approximately
equal duration.
The word equinox comes from this definition, derived
from the Latin aqueous (equal) and nox (night). The
equinox is not exactly the same as the day when
period of daytime and night are of equal length for
two reasons.
