Reggie Smith, age 12, of Allston., Mass., for his question:
Why do we have winter and summer?
The earth runs through four changing seasons as it makes orie yearly orbit around the sun. In the southern hemisphere, the seasons axe the opposite of our seasons north of the equator. Australia has winter while we are enjoying summer. The North Pole is suffering through the long winter night while the south pole is enjoying its long, long summer day.
The earth gets its heat from the sun, and we get heat during the summer season. Are we closer to the sun at this time of year? No, we are 3 million miles closer to the sun on Jan. 1 than we are on July 1. What's more, the southern hemisphere has its winter while we are having summer. The difference in the distance between the Earth and the sun do not cause the changing seasons. The amount of heat we get from the sun depends upon the direction from which the rays strike the surface of the earth. In June, one hour of calm sunshine is three times hotter than one hour of January sunshine. This is because the summer sun is higher in the sky. Its noonday sunbeams are almost directly overhead. When the noon sun is lower in the sky, its rays must slope down through a thick blanket of atmosphere.
As winter changes to summer, the sun rides higher and higher in the sky, and the days grow longer than the nights. As summer changes to winter, the sun rides lower in the sky, and the days get shorter. This variation is caused by the rotation and the revolution of the earth.
The earth rotates once every 24 hours on its axis which is a line through the globe from pole to pole. The earth revolves once each year around its orbit which Circles the sun. It rotates as it revolves. The plane of the orbit gives us a flat surface. You might expect the earth's axis to be straight up or perpendicular to this plane, but it is not. The axis is ti1ted 23.5 degrees from the line perpendicular to the plane of its orbit.
The earth leans a little as it orbits the sun. This means that in June the North Pole is tilted toward the sun, and the south pole is tilted away from the sun. North of the equator, the sun climbs higher in the sky; south of the equator, the noon sun is lower in the sky. As the earth orbits, it bows to the sun with first one pole, then the other. These two points are on the opposite sides of the orbit. As the earth travels between Mid summer and mid winter, the two hemispheres enjoy the moderate season of spring and fall. And twice each year the entire globe enjoys an equinox when day and night are equal.