2018 Winter Solstice Happens Friday, Dec. 21, in Northern Hemisphere

Summary: The 2018 winter solstice happens Friday, Dec. 21, in the Northern Hemisphere while the Southern Hemisphere experiences the event as a summer solstice.

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

The 2018 winter solstice happens Friday, Dec. 21, in the Northern Hemisphere at 22:22 Coordinated Universal Time (5:22 p.m. Eastern Standard Time) and simultaneously opens astronomical summer in the Southern Hemisphere, where the event occurs as a summer solstice.

The 2018 winter solstice takes place either Friday, Dec. 21, or Saturday, Dec. 22. The world’s time zones convert Coordinated Universal Time (UTC), the world’s official time standard, into local times. Local time zones determine the occurrence of the 2018 December solstice as a Friday, Dec. 21, event or as a Saturday, Dec. 22, event.

Time zones express time ahead or behind Coordinated Universal Time, known as offsets, with positive or negative offsets, respectively. Time zones that are behind Coordinated Universal Time range in offsets from UTC-1 to UTC-12. Time zones that are ahead of Coordinated Universal Time range in offsets from UTC+1 to UTC+14.

The 2018 December solstice takes place Friday in all time zones with a negative offset. The 2018 December solstice also has a Friday occurrence in Greenwich Mean Time, the time zone that equates to Coordinated Universal Time. The offset of UTC+0 represents the Greenwich Mean Time Zone’s offset.

The 2018 December solstice occurs Friday for UTC+1 time zones. UTC+1 time zones add only one hour to Coordinated Universal Time. The 2018 December solstice takes place at 11:22 p.m. Friday, Dec. 21, in UTC+1 time zones. Central European Time (CET) and West Africa Time (WAT) are UTC+1 time zones.

The 2018 December solstice happens Saturday in time zones that are ahead of Coordinated Universal Time by two or more hours. Time zones with positive offsets ranging from UTC+2 to UTC+14 experience the 2018 December solstice as a Saturday event.

Saturday, Dec. 22, at 12:22 a.m. is the instant of the 2018 December solstice for UTC+2 time zones. UTC+2 time zones include Western European Time (WET), Eastern European Time (EET), Central Africa Time (CAT) and South African Standard Time (SAST). The 2018 December solstice happens as a summer solstice for most countries in the Central Africa Time zone and for all places in the South African Standard Time zone.

UTC+14 time zones claim the latest local time assigned to the 2018 December solstice. The event is timed for 12:22 p.m., Saturday, Dec. 22, in places observing UTC+14. Line Islands Time (LINT) and West Samoa Time (WST) are UTC+14 time zones. For some places in the UTC+14 time zones, such as the Southern Line Islands and the Independent State of Samoa (West Samoa), the December solstice opens astronomical summer. The December solstice opens astronomical winter for other locations in the UTC+14 time zones, such as the Northern Line Islands.

The December solstice occurs annually as the second of two solstices. The year’s first solstice takes place in June. The June solstice opens astronomical summer in the Northern Hemisphere and astronomical winter in the Southern Hemisphere.

The twice yearly astronomical events reflect the sun’s most northerly or southerly reaches with respect to the celestial sphere’s celestial equator. The celestial sphere is an abstract sphere imagined from Earth’s surface outward into space for astronomy and navigation. The celestial equator represents the outward projection of Earth’s equator onto the celestial sphere.

During the solstices, Earth’s Northern Hemisphere and Southern Hemisphere receive different amounts of sunlight as a function of Earth’s tilted axis. The axis, an imaginary line running through Earth and emerging at the poles, tilts maximally toward or away from the sun. During the December solstice, the South Pole exhibits maximum tilt toward the sun while the North Pole displays maximum tilt away from the sun. Consequently, sunlight directed toward the Southern Hemisphere exceeds the Northern Hemisphere’s receipt of sunlight.

The June solstice offsets the Northern Hemisphere’s December sunlight deficit. During the June solstice, the axis point at the North Pole bows maximally toward the sun while the South Pole’s tilt inclines maximally away from the sun. Consequently, the maximum sunlight reception favors the Northern Hemisphere.

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

the year’s seasonal pairings of equinoxes and solstices: Henry Kiddle’s A New Manual of the Elements of Astronomy, Descriptive and Mathematical (1877), page 83: Not in copyright, via Internet Archive

Acknowledgment

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

Image credits:

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

the year’s seasonal pairings of equinoxes and solstices: Henry Kiddle’s A New Manual of the Elements of Astronomy, Descriptive and Mathematical (1877), page 83: Not in copyright, via Internet Archive @ https://archive.org/stream/anewmanualeleme01kiddgoog#page/n88/mode/2up

For further information:

“10 Things About the December Solstice.” Time And Date > Sun & Moon.
Available @ http://www.timeanddate.com/calendar/ten-things-december-solstice.html

Byrd, Deborah. “Solstice Arrives December 21.” EarthSky > Astronomy Essentials > Earth. Dec. 21, 2017.
Available @ http://earthsky.org/astronomy-essentials/everything-you-need-to-know-december-solstice

EarthSky. “When Is My Earliest Sunset?” EarthSky > Earth. Nov. 28, 2017.
Available @ http://earthsky.org/earth/winter-solstice-and-late-sunrise</

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

Kiddle, Henry. A New Manual of the Elements of Astronomy, Descriptive and Mathematical: Comprising the Latest Discoveries and Theoretic Views: With Directions for the Use of the Globes and for Studying the Constellations. New York, NY: Ivison, Blakeman, and Co.; Chicago IL: S.C. Griggs and Co., 1877.
Available via Internet Archive @ https://archive.org/details/anewmanualeleme01kiddgoog

Marriner, Derdriu. “2017 Winter Solstice Happens Thursday, Dec. 21, in Northern Hemisphere.” Earth and Space News. Wednesday, Dec. 20, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/12/2017-winter-solstice-happens-thursday.html

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. “December Solstice Opens Astronomical Winter With 2016’s Longest Night.” Earth and Space News. Wednesday, Dec. 14, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/12/december-solstice-opens-astronomical.html

Marriner, Derdriu. “December Winter Solstice Opens Northern Hemisphere’s Shortest Season.” Earth and Space News. Wednesday, Dec. 21, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/12/december-winter-solstice-opens-northern.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

McClure, Bruce. “Believe It Or Not, Whole Earth Has Longest Days at Solstice-Time.” EarthSky > Tonight. Dec. 19, 2017.
Available @ http://earthsky.org/tonight/longest-days-of-year-accompany-the-december-solstice

McClure, Bruce. “December Solstice Starts Shortest Season.” EarthSky > Tonight. Dec. 18, 2017.
Available @ http://earthsky.org/tonight/years-shortest-season-starts-with-december-solstice

“Winter Solstice -- Shortest Day of the Year.” Time And Date > Sun & Moon.
Available @ http://www.timeanddate.com/calendar/winter-solstice.html