What is the season after summer

Why are there seasons?

The reason for the change from winter, spring, summer and autumn is the oblique axis of the earth. But other factors also influence the seasonal fluctuations in the weather.

As is well known, the earth revolves around itself and at the same time orbits the sun. The axis of our planet is inclined by 23.5 degrees compared to the axis of rotation of its movement around the sun. During the annual orbit, both the angle of incidence of sunlight and the duration of the day fluctuate - at every point on earth: In one half of the year the northern hemisphere is inclined towards the sun, in the other half the southern hemisphere. The higher the position of the sun and the longer the day, the more the air warms up. As a result, the well-known cycle of the seasons arises in the middle and high latitudes.

In the northern hemisphere, the sun reaches its highest level around June 21st. Then the days are the longest. Then the duration of the day decreases, and around September 22nd there is an equinox: day and night are exactly the same length - everywhere on earth. After all, the night around December 21st is the longest, and the sun is not very high above the horizon, even at noon. It even disappears completely north of the Arctic Circle. After the so-called winter solstice, spring approaches - the days are getting longer and the sun is rising higher and higher. There is another equinox around March 21st. The cycle ends with the next summer solstice.

In the southern hemisphere it is exactly the opposite: the winter solstice there is around June 21st, the summer solstice around December 21st. Except for the fact that the seasons are shifted by six months, there is no difference to the northern hemisphere. The tropics are an exception: seasons like those in the middle and high latitudes are unknown there; instead there are rainy seasons there. Between the two tropics, which run parallel to the equatorial plane at 23.5 degrees north and south, the sun is always quite high.

One could assume that our latitudes are coldest at winter solstice and warmest at summer solstice. But actually the seasons that we perceive in the northern hemisphere are shifted in time compared to the astronomical data: the coldest winter months always follow after the winter solstice, the warmest summer months after the summer solstice. And that is due to the high heat capacity of water.

Orbit of the earth around the sun

In spring, the sun is high above the horizon and its light falls at a steep angle on the surface of oceans and lakes. As a result, the water masses heat up significantly more than in the winter months. However, since water can absorb significantly more heat per volume than air, for example, it takes months to heat it up. The highest water temperatures are therefore only expected towards the end of summer. The air that sweeps over the sea and assumes its temperature then flows over the land. For this reason, the warming over the continents is also delayed.

The lagging warming of the sea water is also responsible for the fact that the Arctic sea ice does not reach its minimum until September, not in June. It can also explain why the seasons in the southern hemisphere differ less from each other than in the northern hemisphere: The proportion of sea on the earth's surface is much higher there. This dampens the annual temperature cycle.

The calendar dates of the seasons are based on the astronomical turning points - i.e. on four different sections of the earth's orbit. Due to this definition, however, the seasons vary in length - because the orbit of our home planet is slightly elliptical and the orbital speed of the earth fluctuates as a result: in early January it reaches its point closest to the sun and is fastest on the move, in early July - when it passes the point furthest from the sun - on the other hand, the slowest. That is why the calendar summer lasts 94 days. Spring is 93 days long. Autumn and winter, on the other hand, are 89 days short.

Meteorologists determine the four seasons in a different way. They are based on the division of the year into twelve months and the climatic conditions that prevail in them. For meteorologists, spring, for example, lasts from March 1st to May 31st, while in calendar terms it does not follow until three weeks later.

One should not attach too much importance to the different definitions of the seasons. Ultimately, the four seasons merge continuously. We humans have only artificially divided this course into four sections. A division into a winter half-year and a summer half-year would have been just as possible.