Global Warming - Sun's Influences on the Earth
The Sun's influences on the
Earth are numerous. The sun radiates light, which combined with the rotation of
the Earth on its axis, causes day and night. It also radiates heat, which with
the revolution of the Earth around the Sun and the inclination of the Earth's
axis, causes the changing of the seasons. The most light and heat come from
direct rays of the Sun.
The rays of the Sun can reach
only half of the Earth's surface at one time. The sun's rays extend to the North
and South Poles equally only twice during the year, on September 23 and March
21. (Figure 4) On these two days the vertical rays of the Sun fall directly on
the Equator. From September 23 to December 21, the Sun's rays gradually extend a
few degrees beyond the South pole and recede from the North Pole. On December
21, the rays extend 23 1/2 beyond the South Pole and fail to reach the North
Pole by the same number of degrees. At this time, the area surrounding the South
Pole known as the Antarctic Circle, receives sunlight and the Arctic Circle,
surrounding the North Pole, is without sunlight.
On December 22, the Sun's
rays begin to simultaneously enter the Antarctic Circle and simultaneously
enter the Arctic Circle. (Figure 5) On June 20, the rays have receded
entirely from the Antarctic Circle and extend 23 1/2 beyond the North Pole.
Now the South Pole is in darkness and the North Pole receives constant
sunlight. This explains the six-month day and night at the North and South
When the light shines
directly on the line marking the Tropic of Cancer (23 1/2 beyond the North
Pole). Now the South Pole is in the darkness and the North Pole receives
constant sunlight. This explains the six-month day and night at the North
and South Poles.
When the light shines
directly on the line marking the Tropic of Cancer (23 1/2 north of the
equator) the South Pole is in darkness and the entire Arctic Circle receives
the Sun's rays. At this time day and night are equal on the Equator, night
is shorter than day in the Southern Hemisphere, and longer than day in the
Earth's Position by Months in Relation to the Sun
One-half of the Earth receives the Sun's rays
and has daylight while the other half has darkness. As the Earth is
constantly rotating (from west to east), the lighted half of the Earth is
the same only for an instant of time. The constant inclination of Earth on
its axis of rotation while it revolves around the Sun accounts for the North
Pole's gradual change from a position of 23 1/2 toward the sun to one of 23
1/2 away from the sun. The portion of the Earth from the Arctic Circle (66
1/2 N) south to the Antarctic Circle (66 1/2S) has light and darkness in
every 24-hour period throughout the year. The Areas within the Artic Circle
and the Antarctic Circle (23 1/2 from the Poles) have periods of continuous
darkness exceeding 24 hours that increase from one day to the maximum of six
months at the poles.
Equinoxes and Solstices determine the
seasons. Equinox is a Latin word meaning "equal nights." March 21 and
September 23 are called Equinoxes because on these two dates the days
and nights are of equal length throughout the world. March 21 is the
vernal equinox and September 23 is the autumnal equinox.
These dates will occasionally vary by one day.
Solstice is a
Latin word meaning "sun stand still." June 20 and December 21 are
northern and southern limits respectively and seem to stop for a moment
before moving back toward the Equator. June 21 is the summer solstice
and vise versa for December 21. In the Northern Hemisphere spring last
from March 21 to June 21, summer from June 21 to September 23, autumn
from September 23 to December 21, and winter from December 21 to March
21. The seasons are the opposite in the Southern Hemisphere.
Temperature and Earth
The heat of the Sun
depends upon the directness of its rays. This explains why it is warmer
at the Equator and colder at the poles. It also explains why it is
hotter when the sun is overhead then at any other time during the day.
At noon, any spot on the Earth's surface is receiving the direct, or
more nearly direct, rays of the sun that at any other time of the day.
The most intense heat will be found in the area where the vertical rays
of the Sun fall.
The rays of the Sun
must pass through the Earth's atmospheric layer. When they are falling
obliquely, they must pierce more of its atmosphere, and the intensity of
their heat will be lessened.
During the summer
months in the Northern Hemisphere this atmospheric layer acts as a
blanket to hold the heat in. It would seem that since the Sun's rays
have been coming closer since March 21, that June 21 (the longest day of
the year), would be the warmest. This is not true. The months of July an
August are the warmest months.
During the months from March
to June the days have been longer and the nights shorter, but the Earth is so
cold from the winter months that it takes time to heat. The Earth absorbs more
heat during these long days than it can give off during the short nights.
In July and August, the Earth
has absorbed so much excess heat that it must give some off during the days as
well as the nights. The atmosphere is then acting as blanket to retain the heat
rather than give it off. This same thing is true in the Southern Hemisphere.
Although December is the height of summer in this hemisphere, it is not as warm
as January and February.
The above explanation, if
reversed, explains the winter months in this way: January and February are much
colder than December because by the time these months are reached all the heat
stored during the warmer months has been given off during the long nights.
Because the days are so much shorter than the nights, the little heat that might
be absorbed during the day is quickly given off at night.
about measuring distance on a globe.
Learn about the Earth's
Learn how globes show
Learn about the analemma.