2024, January 2: Earth is at Perihelion

January 2, 2024: Earth is at perihelion today – the point on the orbital path closest to the sun.

Earth is at perihelion, the point in the orbit closest to the sun. Aphelion, the point farthest from the sun occurs in over six months.
Chart Caption – 2024, January 2: Earth is at perihelion, the point in the orbit closest to the sun. Aphelion, the point farthest from the sun occurs in over six months.

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by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:18 a.m. CDT; Sunset, 4:31 p.m. CDT.  Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.

Summaries of Current Sky Events
Summary for Venus as a Morning Star, 2023-24

Earth is at Perihelion

black and gray desk globe
Photo Caption – Earth Globe (Photo by lilartsy on)

Earth is at perihelion today at 6:39 p.m. CDT. That is the point in the terrestrial orbit that is closest to the sun.

Earth’s distance from the sun is 0.9833 Astronomical Unit (A.U.) or 91.5 million miles.

Earth is farthest from the sun or at aphelion a few minutes after midnight on July 5th at 1.0167 A.U. or 94.5 million miles.

The planets do not revolve around the sun in perfect circles.  Rather, the orbits are ellipses.  Make an ellipse with a loop of string and two thumb tacks.  Poke the tacks into a sheet of cardboard and stretch the string taught with a pencil.  While holding the string in a tight loop, move the pencil in a rotary motion until an ellipse is made.

While the distance varies around three million miles during the course of a year, Earth’s orbit is 98% circular.  Only Venus has a more circular orbital pathway. 

Mars’ Eccentric Orbit

Mars at opposition, 2016 and 2018
These side-by-side images of Mars, taken roughly two years apart, show very different views of the same hemisphere of Mars. Both were captured when Mars was near opposition, which occurs about every two years, when Earth’s orbit catches up to Mars’ orbit. At that time, the Sun, Earth, and Mars fall in a straight line, with Mars and the Sun on “opposing” sides of Earth. (NASA Photo)

Mars orbit is 90% circular.  If the Red Planet is near perihelion when Earth passes between it and the sun, this event is known as a perihelic opposition. Such close oppositions occur every 15-17 years, with the last one in 2018.  Before spacecraft visited the planet, Earth-based telescopes made historic observations of the planet.

At the 1877 close opposition, Phobos and Deimos, the planet’s moon duo, were first observed.  During the 1894 Mars opposition, Percival Lowell first began to document his later-disproved discovery of “canals.”  

Mercury, the solar-system’s innermost planet’s orbit is only 80% circular, while the classic ninth planet Pluto’s orbit is 75% circular.

Comet Orbits

Comet West was discovered in photographs by Richard West on August 10, 1975. It reached peak brightness in March 1976. During its peak brightness, observers reported that it was bright enough to study during full daylight. Despite its spectacular appearance, it did't cause much expectation among the popular media. The comet has an estimated orbital period of 558,000 years.
Photo Caption – Comet West was discovered in photographs by Richard West on August 10, 1975. It reached peak brightness in March 1976. During its peak brightness, observers reported that it was bright enough to study during full daylight. Despite its spectacular appearance, it didn’t cause much expectation among the popular media. The comet has an estimated orbital period of 558,000 years. (Photo Credit: European Southern Observatory)

In comparison, comet orbits can be highly eccentric or out of round.  Comet Halley, the most famous comet, has an orbit that is only 3% circular.  Its aphelion point is 35 A.U., beyond Neptune’s orbit.  The comet passed that point last month and began its return trip toward perihelion, 0.593 A.U. inside Venus’ orbit in 2061.

Earth is at perihelion today.  So, happy Earth at Perihelion Day!

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