12 Days After June Solstice Earth Reaches 2017 Aphelion Monday, July 3

Summary: Earth reaches 2017 aphelion Monday, July 3, at 20:11 Coordinated Universal Time, 12 days after the June solstice.

Earth’s elliptical orbit around the sun accounts for points of least and greatest center-to-center distances between the two celestial bodies; mean values for the orbit’s two extremes are 152,000,000+ kilometers for aphelion and 147,000,000+ kilometers for perihelion: Gothika (vector image from Horst Frank/German Wikipedia drawing), CC BY SA 3.0 Unported, via Wikimedia Commons

Earth reaches 2017 aphelion Monday, July 3, at 20:11 Coordinated Universal Time (4:11 p.m. Eastern Daylight Time), 12 days after the June solstice.

The mid-year solstice that opens astronomical summer in the Northern Hemisphere and astronomical winter in the Southern Hemisphere takes place Wednesday, June 21, at 4:24 a.m., according to Coordinated Universal Time (UTC), the world’s official time standard. The world’s local time zones either place the astronomical event one day earlier, on Tuesday, June 20, or coincide with the UTC date but may differ in the time at which the solstice occurs.

The attainments of aphelion, which is the farthest center-to-center distance between Earth and sun, and of perihelion, the closest center-to-center distance between the two celestial bodies, usually occur within about two weeks of the year’s two solstices. Aphelion is reached after the June solstice. Perihelion is attained after the December solstice.

Earth does not experience a consistent center-to-center distance from the sun because the Earthly orbit is not circular. Earth’s orbit is somewhat elliptical because of disturbances, known as perturbations, from outside forces or influences. For example, Earth’s moon acts as a perturbing influence on Earth’s orbit around the sun. An elliptical orbit displays two extreme points, termed apsis in the singular and apsides in the plural. Apsides (Ancient Greek ἁψίς, hapsís, “arch, vault”) for a celestial body’s orbit around the sun are identified as aphelion (Ancient Greek: ἀπό, apó, “from” + ἥλιος, hḗlios, “sun”) and perihelion (Ancient Greek: περί, perí, “near” + ἥλιος, hḗlios, “sun”).

Deviations, known as eccentricities, in Earth’s orbit account for annual variations in aphelic and perihelic distances. Retired NASA astrophysicist Fred Espenak notes that the current mean eccentricity of Earth’s orbit is 0.0167. An eccentricity of zero represents a circular orbit while numbers higher than zero denote somewhat elliptical orbits.

Astronomers express distances between Earth and sun in astronomical units (AU). An astronomical unit equates to the mean distance between Earth and sun. In 2012, the International Astronomical Union valued 1 AU at 149,597,870,700 meters, which equals 149,597,870.70 kilometers (roughly 92,955,807 miles). Espenak lists mean values of 1.0167103 AU (152,097,701 kilometers) at aphelion and of 0.9832899 AU (147,098,074 kilometers) at perihelion.

Earth’s 2017 aphelion marks a center-to-center distance of 1.0166756 AU (roughly 152,092,511 kilometers). Norway-based Time And Date website expresses the distance as 94,505,901 miles.

Espenak’s table of closest (perihelion) and farthest (aphelion) distances for the 21st century notes that the 2017 aphelion of 1.0166756 AU (152,092,504.953 kilometers) is 5,190 kilometers less than the mean aphelion of 1.0167103 AU (152,097,701 kilometers).

The 21st century, which spans Jan. 1, 2001, through Dec. 31, 2100, exhibits minimum and maximum extremes in aphelion. Minimum aphelion represents the lowest value. Maximum aphelion represents the highest value.

The 21st century’s minimum aphelion happens Wednesday, July 4, 2085, at 21:34 UTC (5:34 p.m. EDT). Minimum aphelion marks a distance of 1.0166125 AU (roughly 152,083,067 kilometers). Minimum aphelion of 1.0166125 AU (roughly 152,083,067 kilometers) is 14,634 kilometers less than the mean aphelion of 1.0167103 AU (152,097,701 kilometers).

The 21st century’s maximum aphelion occurs Thursday, July 4, 2019, at 22:11 UTC (6:11 p.m. EDT). Maximum aphelion logs a distance of 1.0167543 AU (roughly 152,104,291 kilometers). Maximum aphelion of 1.0167543 AU (roughly 152,104,291 kilometers) exceeds the mean aphelion of 1.0167103 AU (152,097,701 kilometers) by 6,590 kilometers.

Espenak identifies a difference of 0.0001419 AU (21,225 kilometers) in the range between the 21st century’s maximum aphelion and minimum aphelion.

Aphelion and perihelion are not responsible for Earth’s seasons. The tilt of Earth’s rotational axis accounts for Earthly seasons. Aphelion and perihelion influence the length of Earth’s seasons. Earth moves faster around perihelion (30,300 meters per second), effecting a shorter season, and slower around aphelion (29,300 meters per second), encouraging a longer season.

The takeaway for Earth’s reach of 2017 aphelion Monday, July 3, is the currently predictable occurrence of the annual milestone within two weeks of the year’s June solstice.

Earth view at instant of aphelion, July 3, 2017, at 20:11 UTC (4:11 p.m. EDT), 152,092,511 kilometers above 23 degrees 26 minutes north latitude, 0 degrees west longitude (Tropic of Cancer): John Walker/Earth and Moon Viewer, Public Domain, via Fourmilab Switzerland

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Earth’s elliptical orbit around the sun accounts for points of least and greatest center-to-center distances between the two celestial bodies; mean values for the orbit’s two extremes are 152,000,000+ kilometers for aphelion and 147,000,000+ kilometers for perihelion: Gothika (vector image from Horst Frank/German Wikipedia drawing), CC BY SA 3.0 Unported, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Seasons1.svg

Earth view at instant of aphelion, July 3, 2017, at 20:11 UTC (4:11 p.m. EDT), 152,092,511 kilometers above 23 degrees 26 minutes north latitude, 0 degrees west longitude (Tropic of Cancer): John Walker/Earth and Moon Viewer, Public Domain, via Fourmilab Switzerland @ https://www.fourmilab.ch/cgi-bin/Earth

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