Brrrr !

Illustration: Courtesy of skytonight.com

The Earth revolves on an axis that is tilted 23.5 degrees from the plane of its orbit around the Sun. Thus, as it travels over its elliptical orbit, the angle our Equator makes with the Sun oscillates between 23.5 degrees north and 23.5 degrees south. It is this tilt of the Earth on its axis that produces our four seasons, not our distance from the Sun.

Today, at 7:22 p.m., EST, the Sun shone directly over the Tropic of Capricorn, the latitude that is 23.5 degrees south of the Equator. In the northern hemisphere, this shortest day and longest night of the year marked the beginning of our Winter. The reverse was the case in the southern hemisphere. On this day, the North Pole was sunless for 24 hours and the South Pole had 24 hours of continuous daylight.

From today on, the declination of the Sun in relation to our planet will begin to move northward and on March 21 it will be over the Equator, for the Equinox. On that date, day and night will be exactly equal in duration. Then on June 21, as shown in the picture on the right, the Sun will arrive at the Tropic of Cancer, 23.5 degrees north of the Equator. That will mark the first day of our summer. At that point, the Sun’s declination begins to move southward.

The illustration on the left shows that during Winter, the inclination of our planet’s axis keeps our hemisphere turned away from the Sun. And thus, with shorter days and longer nights, we receive substantially less solar heat than during the summer, when the days are longer.

Now allow yourself to speculate. If the tilt of our planet's axis were several degrees greater or less than 23.5 degrees, what would be the consequences?

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