Environmental Engineering Reference
In-Depth Information
Solstices occur when the sun is most north or south of the celestial equator. In the Northern Hemisphere, the
summer solstice, when the sun is northernmost, occurs on June 21 over the Tropic of Cancer. The winter sol-
stice occurs on December 21 over the Tropic of Capricorn and is when the sun is southernmost. In the North-
ern Hemisphere, the summer solstice is the longest day of the year, and the winter solstice is the shortest.
Seasons
Earth's seasons are created by the tilt of Earth's axis to its orbital plane and its rotation around the sun, which is
23.5 degrees. At different times throughout the year, different parts of the Earth are facing the sun. Summer
occurs when the sun's rays hit Earth's surface at the most direct angles, also giving summer the longest daylight
hours. During winter the angle of the sun's rays are more oblique, giving that portion of the Earth shorter days
and less solar energy. The seasons are not related to Earth's distance from the sun. The Earth is actually closest
to the sun in January ( perihelion ) and farthest away in July ( aphelion ).
The Atmosphere
As a protector of Earth, the atmosphere deflects many harmful UV rays from the sun and helps to maintain a
stable temperature by helping to retain heat with a natural greenhouse effect. Without the atmosphere, life as
we know it would not be able to exist on this planet. It is also a dynamic aspect of Earth, changing over the 4.6
billion years of the planet's existence.
Search WWH ::




Custom Search