April 16-17, 2025: Within 24 hours, Mercury and Mars pass aphelion, the closest points to the sun, dual aphelions.
by Jeffrey L. Hunt
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Planets revolve around the sun in elliptical orbits, so that their distance from the sun is in constant change. On the invisible planetary path, perihelion is the name of the point closest to the sun, while aphelion is the point farthest away.
Planets at Aphelion
Earth is at aphelion on July 3rd, followed by perihelion on January 3rd, 2026.
All the planets’ perihelion and aphelion points are not aligned. Mars’ aphelion occurs 102° from Mercury.
Solar System Distances
In the solar system, distances are measured in astronomical units (A.U.) Earth’s average distance from the sun is defined to be 1 A.U., that equals about 93 million miles. The other planets’ distances are measured compared to our planet. Mercury’s average distance is 0.387 A.U. and Neptune’s is 30.12 A.U. In short, Mercury is about 40% of Earth’s solar distance, while Neptune is 30 times farther away from the sun.
Earth’s distance ranges from 0.983 A.U. to 1.017 A.U.
Mars reaches its most distant point on the 16th, at a solar distance of 1.666 A.U., while Mercury is farthest from the sun on the 17th at 0.467 A.U.
Martian Perihelic Oppositions
Mars reaches aphelion again on March 4, 2027, following its opposition on February 19th, when Earth is between the planet and Sun. Such events occurring near aphelion are known as aphelic oppositions, compared to those occurring near perihelion or perihelic oppositions.
When at a perihelic opposition, Mars is closest to Earth and nearly at its brightest. Before the invention of robot spacecraft, Martian moons were first observed through telescopes, as well as features that were misinterpreted as canals, supposedly constructed by intelligent Martians.
Mercury is at aphelion again on July 14th, from its rapid revolution around the sun.
Mars and Mercury are at aphelion, the points farthest from the sun, within about 24 hours, a dual aphelion.
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