[Physics Class Notes] on Aphelion Pdf for Exam

We know that all planets, asteroids, and comets in the solar system revolve around the Sun in approximately elliptical orbits. Thus as a result there are points in the orbital pathways when the heavenly body is farthest and nearest to the sun. Aphelion is when a planet, an asteroid, or a comet is most distant from the sun in its orbit. This is the aphelion definition in astronomy. This answers the question of what is aphelion. All planets in the solar system have an aphelion. The perihelion condition is the exact opposite. The tilt of the axis of the planet and the elliptical orbital pathways cause aphelion and perihelion.

Perihelion and Aphelion of the Earth

Perihelion is the point in the orbital pathway of earth where it is closest to the sun. The distance is approximately 91.4 million miles or 147 million kilometers. Aphelion on the other hand is the point in the orbit when the earth is farthest away from the sun. The distance is approximately 94.5 million miles or 152million kilometers. Aphelion occurs around July 4 about two weeks after the June Solstice. Perihelion occurs around January 3 after about two weeks of the December Solstice. The aphelion and perihelion occur around the same time every year. This 2021, aphelion of Earth was observed on July 5, at 6.27 P.M (Eastern Time) and perihelion of Earth was observed on January 2, at 8,52 A.M (Eastern Time). The precession of the perihelion events is the reason why the orbit is not a simple closed curve such as an ellipse. Milankovitch Cycles occur because of these events.

Earth’s orbital pathway around the sun cannot be described as a perfect circle. The orbital path is an elliptical one with an eccentricity of 0.017. Therefore the sun will not be at the center. According to the laws of Johannes Kepler, all planets in the Solar system have elliptical orbits with the Sun at one of the focal points. Now due to this reason at times, Earth will be closer to the sun and at times it will drift far away from the sun. Thus we can confirm that the elliptical orbit of the earth around the sun is the cause for aphelion and perihelion. Another cause for this perihelion and aphelion may be the 23.5-degree tilt of the axis of Earth. This tilt results in the changing of the seasons.

When the earth is closest to the sun i.e. during aphelion, the northern hemisphere has a winter season, and the southern hemisphere experiences the summer season. Thus it can be seen that the distance between the earth and the sun does cause any noticeable effect in the changing of the seasons. The minor effects of the difference in distances are overshadowed by the oceanic southern hemisphere and the continental northern hemisphere. Hence the change of the seasons is due to the rotation of the earth around its tilted axis. The tilt is measured to be 23.5 degrees. This is the reason for winter in the northern hemisphere in December – January and summer in the southern hemisphere as the Sun is farther south during this time. The part of the earth where sun rays fall slantingly experience winter whereas the parts where the sun rays fall directly experience the summer season.

Did You Know? 

• The words “ perihelion” and “ aphelion” are derived from ancient Greek, where “apo” means far, “peri” means close, and “helios” stands for the sun.

• All planets, comets, and asteroids in the solar system have approximately elliptical orbits and thus also have a perihelion and aphelion.