Two Weeks After the 2018 December Solstice Earth Reaches Perihelion

Summary: On Thursday, Jan. 3, 2019, two weeks after the 2018 December solstice, Earth reaches perihelion, Earth’s closest center-to-center point with the sun.

Center-to-center distance between Earth and sun in 2019 is closest, Thursday, Jan. 3, at 05:20 Coordinated Universal Time: (5:22 p.m. Eastern Standard Time): Grant Gilmore @grant_gilmore via Twitter July 6, 2018

At 05:20 Coordinated Universal Time (12:20 a.m. Eastern Standard Time), Thursday, Jan. 3, 2019, two weeks after the 2018 December solstice, Earth reaches perihelion, the closest center-to-center point in Earth’s orbit around the sun.

Perihelion in January 2019 equates to 0.9833012 astronomical units (AU), according to retired NASA astrophysicist Fred Espenak’s Astro Pixels website. An astronomical unit (symbol: au, ua or AU) is the unit of measure used by astronomers to express distances between Earth and sun. The unit represents the mean distance between Earth and sun. In 2012, the International Astronomical Union (IAU) established the value of one astronomical unit at 149,597,870,700 meters. One astronomical unit equals 149,597,870.70 kilometers or 92,955,807 miles.

The 2018 December solstice took place Friday, Dec. 21, at 22:22 Coordinated Universal Time (5:22 p.m. Eastern Standard Time). The December solstice opens astronomical winter in the Northern Hemisphere and astronomical summer in the Southern Hemisphere.

Earth’s revolutions around the sun trace an elliptical path. Unlike a circle, an ellipse does not allow for equal distances between the center and the boundary. The oval shape of Earth’s path accounts for two extremes, aphelion and perihelion. Aphelion (Ancient Greek ἀπό, apó, “from” + ἠέλιος, ēélios, “sun”) designates the farthest point in the center-to-center distance between Earth and sun. Perihelion (Ancient Greek: περί, perí, “near” + ἠέλιος, ēélios, “sun”) references the closest point in the center-to-center distance between Earth and sun.

Espenak notes that perihelion distance is not a constant. Lunar and planetary gravitational perturbations cause variations in Earth’s actual distance at perihelion. He considers extreme values of perihelion over a 200-year period between 1901 and 2100. Perihelion distances range from 0.9831914 astronomical units (147,083,346 kilometers) to 0.9833860 astronomical units (147,112,452 kilometers. Espenak calculates a mean perihelion distance of 0.9832899 astronomical units (147,098,074 kilometers).

The January 2019 perihelion is farther than the January 2018 perihelion. January 2019’s perihelion of 0.9833012 astronomical units exceeds January 2018’s perihelion of 0.9832843 astronomical units by 0.0000169 astronomical units. January 2018’s perihelion occurred Wednesday, Jan. 3, at 05:35 UTC (12:35 a.m. Eastern Standard Time).

The January 2019 perihelion is farther than the next perihelion. The January 2020 perihelion will be 0.9832436 astronomical units. The January 2019 perihelion of 0.9833012 astronomical units exceeds the January 2020 perihelion of 0.9832436 astronomical units by 0.0000576 astronomical units. Earth’s reach of January 2020’s perihelion distance is expected Sunday, Jan. 5, 2020, at 07:48 UTC (02:48 a.m. EST).

Espenak’s Earth at Perihelion and Aphelion: 2001 to 2100 chart includes the relative distance of perihelions, in kilometers, with regard to their mean distances. The January 2019 perihelion of 0.9833012 astronomical units varies from the mean distance by 1,681 kilometers. The January 2018 perihelion of 0.9832843 astronomical units varies from the mean distance by minus 845 kilometers. The January 2020 perihelion of 0.9832436 astronomical units varies from the mean distance by minus 6,935 kilometers.

Espenak also indicates the perihelion interval between current and previous perihelions. He finds that 364.99 days elapse between 2019’s reach of perihelion Thursday, Jan. 3, at 05:20 UTC (12:20 a.m. EST) and 2018’s reach of perihelion Wednesday, Jan. 3, at 05:35 UTC (12:35 a.m. EST). The January 2020 perihelion happens 367.10 days after the January 2019 perihelion.

Espenak’s Astro Pixels website calculates the interval range during the 21st century at 363.08 to 367.86 days. The lowest interval of 363.08 days occurs between the January 2088 and the January 2089 perihelions. The 2088 perihelion occurs Monday, Jan. 5, 2088, at 14:59 UTC (9:59 a.m. EST). Earth reaches the 2089 perihelion Sunday, Jan. 2, 2089, at 17:01 UTC (12:01 p.m. EST).

The highest interval of 367.88 days occurs between the January 2073 and the January 2074 perihelions. The 2073 perihelion happens Monday, Jan. 2, 2073, at 14:41 UTC (9:41 a.m. EST). The 2074 perihelion occurs Friday, Jan. 5, 2074, at 11:25 UTC (6:25 a.m. EST).

The takeaway for Earth’s reach of perihelion two weeks after the 2018 December solstice, which occurred Friday, Dec. 21, at 22:22 Coordinated Universal Time (5:22 p.m. Eastern Standard Time), is that the 2019 perihelion happens Thursday, Jan. 3, 2019, at 05:20 UTC (12:20 a.m. EST).

December 2018's solstice precedes Earth's perihelion (closest center-to-center distance with the sun) by two weeks; sunlit Earth, December solstice, Dec. 21, 2010; imaged by Spinning Enhanced Visible and Infrared Imager (SEVIRI) on EUMETSAT’s (European Organisation for the Exploitation of Meteorological Satellites) Meteorsat-9: via NASA Earth Observatory

Acknowledgment

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

Image credits:

Center-to-center distance between Earth and sun in 2019 is closest, Thursday, Jan. 3, at 05:20 Coordinated Universal Time: (5:22 p.m. Eastern Standard Time): Grant Gilmore @grant_gilmore via Twitter July 6, 2018, @ https://twitter.com/grant_gilmore/status/1015307943665954822

December 2018's solstice precedes Earth's perihelion (closest center-to-center distance with the sun) by two weeks; sunlit Earth, December solstice, Dec. 21, 2010; imaged by Spinning Enhanced Visible and Infrared Imager (SEVIRI) on EUMETSAT’s (European Organisation for the Exploitation of Meteorological Satellites) Meteorsat-9: via NASA Earth Observatory @ https://earthobservatory.nasa.gov/images/52248

For further information:

“Astronomical Unit (AU).” NASA Jet Propulsion Laboratory Near Earth Object Program > Glossary.
Available @ http://neo.jpl.nasa.gov/glossary/au.html

EarthSky. “Are the December Solstice and January Perihelion Related?” EarthSky > Astronomy Essentials > Space. Dec. 31, 2015.
Available @ http://earthsky.org/space/are-the-december-solstice-and-the-january-perihelion-related

EarthSky. “Why Aren’t the Earliest Sunsets on the Shortest Day?” EarthSky > Earth. Dec. 7, 2014.
Available @ http://earthsky.org/earth/winter-solstice-and-late-sunrise

Espenak, Fred. “Earth at Perihelion and Aphelion: 2001 to 2100 Greenwich Mean Time.” Astro Pixels > Ephemeris.
Available @ http://www.astropixels.com/ephemeris/perap2001.html

Espenak, Fred. “Solstices and Equinoxes: 2001 to 2100 Greenwich Mean Time.” Astro Pixels > Ephemeris.
Available @ http://www.astropixels.com/ephemeris/soleq2001.html

Grant Gilmore @grant_gilmore. “FRIDAY FUN FACT: Today the Earth was 94,507,803 miles from the Sun as it reached aphelion, its furthest distance from the sun. We’ll be 3.1 million miles closer at perihelion on January 3, 2019.” Twitter. July 6, 2018.
Available @ https://twitter.com/grant_gilmore/status/1015307943665954822

Marriner, Derdriu. “December Solstice Always Occurs at the Same Instant Everywhere on Earth.” Earth and Space News. Wednesday, Nov. 30, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/11/december-solstice-always-occurs-at-same.html

Marriner, Derdriu. "2018 Winter Solstice Happens Friday, Dec. 21, in Northern Hemisphere." Earth and Space News. Wednesday, Dec. 19, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/12/2018-winter-solstice-happens-friday-dec.html

Marriner, Derdriu. "Two Weeks After 2016 December Solstice Earth Reaches 2017 Perihelion." Earth and Space News. Wednesday, Dec. 28, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/12/two-weeks-after-2016-december-solstice.html