What is aphelion and perihelion

Perihelion: closest to the sun

Winter when the earth is closest to the sun?

Despite the short distance to the sun, the northern hemisphere is in deep winter. The astronomical start of winter is reached on December 21st, at the winter solstice. That may all sound strange at first. After all, the closer you get to the sun, the warmer it should be.

The reason that it is still winter north of the equator is due to the inclination of the earth's axis. This does not run vertically during the hike around the sun. It is inclined at 23.4 degrees to the orbit. That is why both hemispheres have opposite seasons.

When the earth is in perihelion, the earth's axis points outwards - away from the sun. The South Pole is facing her. It is now summer in the southern hemisphere. It is true that a little more radiation arrives on earth at perihelion. Since the southern part of the world is covered with more sea areas than the north, it is - despite the proximity to the sun - not warmer there than in summer in the northern hemisphere. This is due to the air, which heats up less quickly over the water masses than over the land masses. When the earth is in aphelion, the earth's axis and its north pole point towards the sun. It is summer in the northern hemisphere and winter in the southern hemisphere.

Why is the earth's axis inclined?

The distance from the sun has hardly any influence on the climate or the seasons. But why is the earth's axis inclined at all? It's because of our moon. Its gravitational forces pull us. Compared to other planets, the moon - in relation to its mother body - is the largest satellite in the solar system. Accordingly, its forces of attraction are also stronger than those of other moons, for example Phobos and Deimos, the moons of Mars.

The moon is our savior. It enables different seasons on earth. Without it, there would be no climate-friendly conditions - the best counterpart to this is Venus, which has no moon and is sizzling hot. In addition to the moon, other celestial bodies have a strong gravitational effect on the earth: On the one hand, Jupiter pulls on the earth's axis, on the other hand, the sun. Without the moon, the earth's axis would go crazy. Life could therefore probably never have come into being.

Sometimes fast, sometimes slowly: the earth

The position of the earth in relation to the sun has another property to show: When the earth is in perihelion, the speed at which it moves around the sun increases. On average, the earth moves on its orbit at 29.7859 kilometers per second. This corresponds to 107,229.24 km / h. For comparison: the Russian hyper-sonic rocket "Avantgarde" can, according to official information, reach about 30,000 km / h. It is one of the fastest man-made objects. However, it cannot compete with the speed of the earth.

When the earth is in perihelion, its speed increases to 30.29 kilometers per second (or 109,044 km / h). When it is in aphelion, its speed decreases. Then it is 29.29 kilometers per second. This corresponds to 105,444 km / h. The difference in speed can be explained with Kepler's third law. It says that the orbital speed of planets decreases as the distance from the sun increases.

By the way: The temporal proximity to the solstices is coincidental. It changes at a rhythm of around 100,000 years.