2025, April 16-17: Dual Aphelions

April 16-17, 2025: Within 24 hours, Mercury and Mars pass aphelion, the closest points to the sun, dual aphelions.

Venus, Jupiter, Mars, Mercury, Regulus, October 15, 2015.
Photo Caption – Venus, Jupiter, Mars, Mercury, Regulus, October 15, 2015.

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by Jeffrey L. Hunt

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Planetary Revolution

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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

In this exaggerated diagram, the relative positions of perihelion, perigee, perigee, and apogee.
Chart Caption: In this exaggerated diagram, the relative positions of perihelion, perigee, perigee, and apogee.(NOAA diagram)

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 and Mercury at aphelion
Chart Caption – 2025, April 16-17: Mars and Mercury reach aphelion within a span of 24 hours.

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 at Perihelion. Lowell and his canals
Photo Caption – Percival Lowell and his map of Mars (Photo Credit: Lowell Observatory)

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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