Earth Sun relationships. With courtesy.

 EARTH-SUN RELATIONSHIPS

It is the earth’s relationship to the sun, and the amount of light it receives, that is responsible for the seasons and biodiversity. The amount of sun a region receives depends on the tilt of the earth’s axis and not its distance from the sun. The northern hemisphere experiences summer during the months of June, July, and August because it is tilted toward the sun and receives the most direct sunlight. Inversely, summer for the southern hemisphere takes place during the months of December, January, and February because that is when it receives the most direct sunlight. Did you know that the earth is approximately 3.2 million miles closer to the sun in January than in June?

Rotation

Rotation describes the circular motion of an object around its center. There are different ways things can rotate.

Rotation of the earth.

A very familiar kind of rotation is when a spherical, three-dimensional object turns around an invisible line inside its center. This center is called an axis. Spinning basketballs turn around an axis. Globes turn around an axis. The Earth itself spins on an axis.

The Earth's axis is vertical, meaning it runs up and down. (A rolling log, on the other hand, has a horizontal axis, meaning it runs sideways.) The Earth's axis runs from the North Pole to the South Pole. It takes the Earth 24 hours, or one day, to make one complete rotation around this invisible line.

As the Earth rotates, each area of its surface gets a turn to face and be warmed by the sun. This is important to all life on Earth. The sun affects everything from the weather we experience to the food we eat, and even our health. If the Earth did not rotate, one half of the Earth would always be hot and bright, and the other part would be frozen and dark.

The Earth also moves around the sun. This movement is called a revolution, which is different from rotation. Objects rotate around an axis, but revolve around other objects. So the Earth rotates around its axis as it revolves around the sun. It takes the Earth 365 days, or one year, to complete a revolution.

Leftover momentum from when planets were forming makes the Earth, and all planets in the solar system, rotate and revolve. As the solar system formed, many moving particles clustered together. They formed a spinning mass. This mass eventually split into different bodies—planets, moons, asteroids, and comets. All these bodies revolve around the sun. In addition, all planets kept their own rotating motion, including the Earth.

The Earth rotates around its axis at a rate of about 1,600 kilometers (1,000 miles) an hour. It revolves around the sun at a rate of 107,800 kilometers (67,000 miles) an hour.

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What Is Earth's Axial Tilt or Obliquity?

By Vigdis Hocken

Earth's Axis Is Imaginary

In astronomy, an axis refers to the imaginary line that an object, usually a planet, rotates around.

Earth's rotational axis is an imaginary straight line that runs through the North and South Pole.  Earth's axis is drawn as a straight red line.

Earth has been orbiting the Sun at a slant. This slant is the axial tilt, also called obliquity.

Earth's obliquity angle is measured from the imaginary line that runs perpendicular to another imaginary line; Earth's ecliptic plane or orbital plane.

At the moment, Earth's obliquity is about 23.4 degrees and decreasing. We say 'at the moment' because the obliquity changes over time, although very, very slowly.

Earth’s Obliquity. 

on 9 November 2021 at noon, Earth's axial tilt, or mean obliquity was 23.43644° or 23°26'11.1".

Earth's mean obliquity today is about 0.00001°, or 0.04", less than 30 days ago.

The Arctic and Antarctic circles today are 1.2 m (4 ft) closer to the poles, and the Tropic of Cancer and Tropic of Capricorn are equally closer to the equator than 30 days ago.

The Tilt Changes

Earth's axial tilt actually oscillates between 22.1 and 24.5 degrees. The reason for this changing obliquity angle is that Earth's axis also wobbles around itself. This wobble motion is called axial precession, also known as precession of the equinoxes. It is caused by the gravitational force from the Sun, the Moon, and other planets.

Axial precession can be described as a slow gyration of Earth's axis about another line intersecting it. A complete wobble of Earth's axis takes around 26,000 years. It outlines the shape of a pair of cones or two spinning tops connected at the tips, which would be at the center of Earth.

Because Earth orbits the Sun at an angle, the solar energy reaching different parts of our planet is not constant, but varies during the course of a year.

This is the reason we have different seasons and why the seasons are opposite in the Northern and Southern Hemispheres.

From the March equinox to the September equinox, the Northern Hemisphere tilts towards the Sun. During this time, there are more than 12 hours of daylight north of the Equator.

At the same time, the Southern Hemisphere tilts away from the Sun, resulting in shorter days.

From the September equinox to the next March equinox, the days are longer south of the equator and shorter north of the equator.