How come we get one summer in a year when earth is revolving in an elliptical orbit around the sun?

Answer 1

Two problems here. First, what causes the seasons. Second, the shape of the earth's orbit. FIRST: CAUSES OF THE SEASONS. The seasons on earth are caused by the tilt of the earth's axis, not by distance from the sun. In fact, in the Northern Hemisphere, the earth is farther from the sun during summer than during winter. Summer occurs when the hemisphere where you live is tilted toward the sun. The sun's rays strike the surface of the earth more directly, and the sun remains above the horizon longer, resulting in greater heating of that part of the earth. Winter occurs when the hemisphere where you live is tilted away from the sun. The sun's rays strike the surface more obliquely, and the sun remains above the horizon for less time each day than in the summer. The result is less heating of that part of the earth. SECOND: THE SHAPE OF EARTH'S ORBIT. The earth's orbit around the sun is pretty nearly circular. It is only very slightly elongated. The distance from the earth to the sun varies between about 147 million kilometers and 152 million kilometers. The difference of five million kilometers sounds like a lot, but it is only three percent of the total distance. This difference in distance does not make a great difference in the warmth or coldness of any part of the earth. But even in the case of an object in a greatly elongated orbit, it still only approaches close to the sun once per "year." The sun is not located at the apparent center of the orbit, but at one of the two foci of the ellipse. This is true of the earth as well, although our orbit is not greatly elongated. The earth approaches "closer" to the sun only once per year, which happens to be at the depth of the Northern Hemisphere's winter (January 2 or 3). There is an odd side effect of the eccentricity of the earth's orbit that you might not read about very often. Any object in orbit moves more rapidly when closer to its parent body and more slowly when farther away. The earth is moving at its fastest during the northern winter, and at its slowest during the northern summer. Thus, the winters in the Northern Hemisphere are a few days shorter than winters in the Southern Hemisphere. Here's another oddity related to the speed of the earth in its orbit. Since the earth is moving faster during our northern winter, and earth's orbit and it's rotation are both counter-clockwise, the solar day (a day measured exactly from one transit of the sun to the next) is a little longer during the winter than it is during the summer. This is not to be confused with the length of daylight during a given day which of course is shorter during our winter. See link for more details.