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Things that Yorams know: why does the earth rotate like shawarma?

Anat wonders: A question we thought about a lot with the children this week: What would happen if the Earth did not rotate on a north-south axis (like a shawarma skewer) but on some axis on the equator?

Earth's axis of rotation. Illustration: shutterstock
Earth's axis of rotation. Illustration: shutterstock

The shawarma image is almost exact but there is room for a little improvement. A shawarma skewer rotates perpendicular to the line between it and the fire, while the earth's axis of rotation is tilted to the side by about 23° from the position of an ideal shawarma axis. If the shawarma oven were a point source of heat, as the sun is for us, we would receive maximum heat at the "equator" of the shawarma all the time, while the "poles" (the north pole of the shawarma covered in fat and the lower south pole) would be relatively cold.

Our skewer, as mentioned, leans slightly to the side and, unlike shawarma, it rotates not only around itself but also around the oven. This position of the axis of rotation gives us the climate zones and the seasons. We have climate zones because the equator receives solar radiation at a low angle and therefore more radiation per unit area and at the poles each unit of radiation is "spread" and spread over a wider area. We have seasons thanks to the deviation from the shawarma state of the axis and the annual journey around the sun, half a year this tilt causes the northern hemisphere to receive stronger radiation and half a year the southern hemisphere gets its share.

If the Earth, similar to what was once thought of the planet Mercury, was an ideal shawarma we would be left with a hot equator and cold poles but without seasons. Every day the sun would shine for 12 hours at every point on the globe. 12 hours would always pass from sunrise to sunset and there was no hotter, colder rainy or cooler season: the chance of rain or hail was the same every day for anyone living at the same distance from the equator. An active atmosphere without seasons exists in the planets Venus and Jupiter, whose rotation axes have an inclination angle of only about 3°.

In chapter 25 of the Book of Genesis, the Creator designates the luminaries first of all "for signs and times and days and years" but it is doubtful if in such a situation, without a shooter and a flock or the seasonal migration of birds, humans would have developed the concept of the year at all. And what would human culture look like in a world without seasons? Let us imagine our coastal plain in constant weather. Assuming that the average temperature and the amount of precipitation would have remained as it was (because the solar radiation per unit area would have been preserved), then every day we would have experienced a maximum temperature of about 530° and the precipitation (XNUMX mm) would have decreased at a constant rate of about one and a half millimeters per day. This is an insignificant drizzle on a mostly sunny day, so most of the rain would have evaporated and not seeped through. Agriculture without a rainy winter was not possible beyond the banks of rivers and with it the wheat and rice civilizations would not have developed. Humans would have been left to live, like their brothers the chimpanzees and gorillas, in small groups near the equator. In higher latitudes there was perpetual cold (although less extreme than the winter prevailing there now) without a summer break allowing for a rich and diverse ecology. In such a world, a culture would not develop that allows you, Anat, to imagine such theoretical questions.

And what about the other extreme? If the axis of rotation was directed towards the sun, the equator would pass through what are today the poles. Half of the globe would experience sunlight for half a year, the temperature at the pole would climb above that of the equator today and the ice cap would disappear completely. In the second half of the dark year, a polar climate would prevail in our hemisphere while the other side would cook. It is hard to imagine how multicellular life would have managed to survive in such a harsh system.

But Anat, there is a reason why the Earth, and the rest of the planets rotate (mostly) like shawarma skewers in relation to the sun and all (almost) in the same direction. All the planets revolve around the sun (to be more precise: revolve around their center of gravity and that of the sun which in our case is very close to the center of the sun) in the same direction which is also the direction of rotation of the sun itself around an axis, they are all approximately in the same plane and the axis of rotation of almost all of them is similar to ours and they are holidays from west to east. The exceptions are Venus, which rotates "upside down", meaning that the sun rises in the west and sets in the east, and Uranus, whose axis of rotation faces the sun.

This uniformity led already in the 18th century (even before Uranus, Neptune, Pluto, the asteroids and most of the planets' moons were discovered) the scientist and mathematician Pierre Laplace to hypothesize about the origin of the solar system "the movements of the planets in one direction and almost in one plane, the movement of the moons in the same direction as the stars Halacht, the rotational movements of these bodies and of the sun on their axis in one direction. From the analysis of the movements of the planets, we conclude that due to extreme heat, the atmosphere of the sun first extended beyond the orbits of the planets. A bit surrounded by clouds.. If we assume that all the stars were formed in this way, then we can imagine their previous nebulous state.."

About 250 years after Laplace it turns out that his speculation was quite good. The solar system was formed about 4 billion years ago from a swirling cloud of gas and dust and our rotation around our axis and around the sun is a continuation of that movement. The deviation of our axis of rotation is explained by most researchers in the collision of a large body that was named "Thea" on the ancient Earth, which except for the deflection of the shawarma skewer, splashed us the moon that surrounds us to this day.

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More of the topic in Hayadan:

4 תגובות

  1. The seasons are not a consequence of the ellipticity of the orbit. The earth's orbit is almost circular and the change of seasons originates from the inclination of the axis of rotation so that each half of the globe receives half a year of solar radiation at a sharper angle. We are closest to the sun in January.

  2. It is not clear why there were no seasons - after all, the earth does not remain at a fixed distance from the sun because its orbit is elliptical. Therefore there was a period when there is more heat coming from the sun and a period when less heat is coming.

  3. Even without the tilt of the axis there were springs, rivers and deltas so that the amount of water was not necessarily uniform in the same latitude

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