What Causes Winter?
As any ten year old can tell us, the Earth
rotates around the sun once every year. At the same time, the planet tilts on
its axis, and this has an even more dramatic effect on the weather. The popular
belief that winter is caused as the Earth moves away from the Sun during the
widest part of its orbit, and thus causes winter, is not true. In actual fact,
winter occurs when the sun is at it's closest point.
The planet tilts 23°27' (23 degrees 27
minutes) and this causes different parts of the Earth's surface to be closer to
the sun at various parts of its orbit. It is this variation that brings about
the seasons. In winter, the northern hemisphere is tilted away from the sun and
thus experiences colder temperatures. Since the southern hemisphere will be
tilted toward the sun at this point, it's seasons are always the opposite of
During the winter, the light rays coming in
from the sun hit the Earth surface at a lower angle. Less energy is transferred
to the surface as a result of the glancing nature of these rays. Basically, the
same amount of light energy is spread out over a larger area. This effect is
compounded by the larger distance this light must travel through the atmosphere,
allowing it to absorb more of this already limited heat.
All Material © Ward Cameron 2005