Philadelphia (WPVI) -- The seasons are caused by the earth being tilted 23.5 degrees on its axis, an imaginary pole that goes through the center of the earth from top to bottom. Earth spins around this pole, making one complete turn each day.
The revolution of the earth around the sun brings us the four seasons: spring, summer, fall and winter.
Because the earth's axis is tilted, we get the four seasons.
In March, the sun's direct rays are over the equator. This marks the arrival of spring in the northern hemisphere and fall in the southern hemisphere. The sun shines equally across all parts of the earth, for approximately 12 hours of light and 12 hours of darkness. This is the vernal equinox.
In June, we have the summer solstice, when the sun's rays are over the Tropic of Cancer. Now, the sun shines directly on the northern hemishere, which is tilted toward the sun, starting summer. The southern hemisphere is tilted away from the sun marking the start of winter.
September brings on the autumnal equinox. Like the vernal equinox, the sun shines directly over the equator, for the arrival of fall in the northern hemisphere and spring in the southern hemisphere.
In December, we have the winter solstice. This is when the sun's rays are directly over the Tropic of Capricorn. The northern hemisphere is tilted away from the sun, marking the arrival of winter and the southern hemisphere is tilted toward the sun, marking the arrival of summer there.
The Earth, the Sun and the Four Seasons - 6abc Weather School
6ABC WEATHER SCHOOL