Artistic Science

kenobi-wan-obi:

Perihelion and Aphelion

The closest point to the Sun in a planet’s orbit is called Perihelion. The furthest point is called Aphelion. The planet moves fastest at perihelion and slowest at aphelion.

GIFs extracted from Year On Earth

Planets in our Solar System orbit the Sun. The orbits of some planets are almost perfect circles, but others are not. Some orbits are shaped more like ovals, or “stretched out” circles.

Scientists call these oval shapes “ellipses”. If a planet’s orbit is a circle, the Sun is at the center of that circle. If, instead, the orbit is an ellipse, the Sun is at a point called the “focus” of the ellipse, which is not quite the same as the center.

Since the Sun is not at the center of an elliptical orbit, the planet moves closer towards and further away from the Sun as it orbits. The place where the planet is closest to the Sun is called perihelion.

When the planet is furthest away from the Sun, it is at aphelion. The words “aphelion” and “perihelion” come from the Greek language. In Greek, “helios” mean Sun, “peri” means near, and “apo” means away from.

(Source: kn207, via kn207)