The key difference between perihelion and aphelion is that perihelion is the point in the orbit of a planet, asteroid or comet that is nearest to the sun, whereas aphelion is the point in the orbit of a planet, asteroid or a comet that is farthest from the sun.
The term apsis refers to either of the two extreme points of the orbit of a planet, an asteroid or a comet that rotates around the sun. For example, it is either the farthest or the nearest point of the orbit of a planetary body. When considering the planets rotating around the sun, the two extreme points are the perihelion and the aphelion, which are the nearest and the farthest points from the sun, respectively.
CONTENTS
1. Overview and Key Difference
2. What is Perihelion
3. What is Aphelion
4. Side by Side Comparison – Perihelion vs Aphelion in Tabular Form
5. Summary
What is Perihelion?
Perihelion is the point in an orbit that is the nearest point to the sun. Generally, we denote the term perihelion using the symbol “q”. The orbit we are considering in this context is the nearest point of a direct orbit of a planet, an asteroid, or a comet that orbits around the sun.
The term perihelion has a Greek origin where “peri-“ means “near” and “helios” mean the Greek god of the sun. Moreover, the Earth comes closest to the sun on 3rd January every year, where Earth occurs at the perihelion point. At this point, the distance between the Earth and the sun is about 91.4 million miles.
What is Aphelion?
Aphelion is the point in an orbit that is the farthest point from the sun. Generally, we denote the term aphelion using the symbol “Q”. The orbit we are considering in this context is the farthest point of a direct orbit of a planet, an asteroid, or a comet that orbits around the sun.
Figure 1: Occurrence of Perihelion and Aphelion on Planetary Orbits
The term aphelion has a Greek origin where “ap-“ means “far” and “helios” mean the Greek god of the sun. Furthermore, the Earth comes to the farthest point of its orbit on 4th July every year, where Earth occurs at the aphelion point. At this point, the distance between the Earth and the sun is about 94.5 million miles.
What is the Difference Between Perihelion and Aphelion?
Perihelion and aphelion come under apsis, which are the extreme points of a planetary orbit. The key difference between perihelion and aphelion is that perihelion is the point in the orbit of a planet, asteroid or comet that is nearest to the sun, whereas aphelion is the point in the orbit of a planet, asteroid or a comet that is farthest from the sun. In other words, perihelion is the nearest point to the sun while aphelion is the farthest point. At perihelion, the distance between the Earth and the sun is 91.4 million miles. At aphelion, the distance between the Earth and the sun is 94.5 million miles.
Below is a summary of the difference between perihelion and aphelion in tabular form.
Summary – Perihelion vs Aphelion
The term apsis refers to either of the two extreme points of the orbit of a planet, an asteroid or a comet that rotates around the sun. Perihelion and aphelion are two such points. The key difference between perihelion and aphelion is that perihelion is the point in the orbit of a planet, asteroid or comet that is nearest to the sun, whereas aphelion is the point in the orbit of a planet, asteroid or a comet that is farthest from the sun.
Reference:
1. “Perihelion.” Wikipedia, Wikimedia Foundation, 24 Feb. 2021, Available here.
Image Courtesy:
1. “Perihelion-Aphelion” By Chris55 – Own work (CC BY-SA 4.0) via Commons Wikimedia