The Rotation of the
Earth around the Sun
The Earth revolves around the sun
and rotates around its own axis. The
orbit of the Earth which is almost
circular is contained in a plane
called the ecliptic.
The Orbit of the Earth
The closest point to the Sun is called
perihelion: the distance Sun-Earth is about 147
millions of km.
We are closest to the Sun in January.
The farthest point to the Sun is called aphelion:
the distance Sun-Earth is about 152 millions of
km.
We are farthest from the Sun in July.
During the equinoxes, the distance Sun-Earth is
about 149.5 millions of km.
The Earth's Tilt
The Earth's axis is tilted about 23.5° from
the perpendicular to the orbit plane.
The tilt of the Earth (and other planets
in the solar system) originates from
collisions with large bodies during the
formation of the planets in the solar
system. The size of the bodies, the angle
of collision determined the tilt and the
rotation of the planets.
The Seasons
The Earth is illuminated by the Sun as it
revolves around it.
Because of the Earth's tilt, on June 21st, the sun
is directly overhead on the tropic of Cancer in
the northern hemisphere and on December 21st,
the sun is directly overhead on the tropic of
Capricorn in the southern hemisphere: this is
the solstice.
In March and September 21st, the sun rays
strike the equator most directly: the Earth is
illuminated from pole to pole: this is the
equinox.
Equator, Tropic of Cancer,
Tropic of Capricorn, Arctic Circle
We all have seen these lines on a map of the world.
The equator
This line is located half way between the poles.
The tropic of Cancer
This line is located 23.5° north of the Equator.
On June 21st, the sun is directly overhead the tropic of
Cancer at noon.
The tropic of Capricorn
This line is located 23.5° south of the Equator.
On December 21st, the sun is directly overhead the tropic
of Capricorn at noon.
The Arctic Circle
This line is located 23.5° south of the North Pole.
What would happen if the Earth's
axis was not tilted?
If the Earth's Axis was
Not Tilted...
It the axis of the Earth was not
tilted, the Earth would receive the
same illumination all year long!