Wednesday, December 20, 2017

2017 Winter Solstice Happens Thursday, Dec. 21, in Northern Hemisphere


Summary: The 2017 winter solstice happens Thursday, Dec. 21, in the Northern Hemisphere at 16:29 Coordinated Universal Time (11:29 a.m. Eastern Standard Time).


map of Earth at instant of southern solstice, Thursday, Dec. 21, at 16:29 Coordinated Universal Time (11:29 a.m. Eastern Standard Time): John Walker/Earth and Moon Viewer, Public Domain, via Fourmilab Switzerland

The 2017 winter solstice happens Thursday, Dec. 21, in the Northern Hemisphere at 16:29 Coordinated Universal Time (11:29 a.m. Eastern Standard Time) and simultaneously opens astronomical summer in the Southern Hemisphere, where the event is known as a summer solstice.
The world’s time zones, which convert the world’s official time standard, Coordinated Universal Time (UTC), into local times, place the 2017 astronomical event either on the same date as UTC, Thursday, Dec. 21, or on the next day, Friday, Dec. 22. Time zones that are eight hours ahead of Coordinated Universal Time experience the 2017 December solstice on Friday, Dec. 22.
The highest time zone is 14 hours ahead of Coordinated Universal Time. With its offset expressed as UTC + 14, the time zone marks the latest local time assigned to the December solstice. The Independent State of Samoa (Malo Sa 'oloto Tuto 'atasi o Sāmoa) observes West Samoa Time, which has a 13-hour offset for standard time and a 14-hour offset for daylight savings. Samoa's 2017 daylight savings time began Sunday, Sept. 24, at 3 a.m. With the 14-hour offset in effect, Samoa observes the late year solstice Friday, Dec. 22, at 6:29 a.m. WST.
Also, as an island country in the Southern Hemisphere, Samoa knows the December solstice as a summer solstice. Samoa’s two main islands and eight small islets straddle the 13th and 14th parallels south of the equator.
In addition to its seasonal designations as the Northern Hemisphere’s winter solstice and the Southern Hemisphere’s summer solstice, the December solstice is also known as the southern solstice. Designation as the southern solstice references the directly overhead position of the sun over the Tropic of Capricorn in the Southern Hemisphere.
The sun’s overhead position directly above a particular point on the Earth’s surface represents the location’s zenith, or highest point, on the imaginary celestial sphere that is projected outward from the Earth. The term subsolar point astronomically designates the point on a planet’s surface touched perpendicularly by the rays of the zenithal sun.
The Tropic of Capricorn claims status as the subsolar point for the December solstice. Currently located latitudinally at 23.43708 degrees south of the equator, the Tropic of Capricorn is also known as the Southern Tropic. The directional designation references the Tropic of Capricorn’s status as indicator of the sun’s most southerly overhead position.
After the December equinox, the subsolar point moves northward from the Tropic of Capricorn to settle at the Southern Tropic’s counterpart in the Northern Hemisphere, the Tropic of Cancer. Known as the Northern Tropic, the Tropic of Cancer currently resides latitudinally at 23.43708 degrees north of the equator. The Northern Tropic marks the most northerly circle of latitude for directly overhead positioning by the sun. The December solstice’s counterpart, the June solstice, witnesses the subsolar point at the Tropic of Cancer.
According to Coordinated Universal Time, in the 21st century, the occurrence of the 2017 southern solstice falls variously on Dec. 20, Dec. 21 or Dec. 22. The Dec. 20 date experiences the event most infrequently, with only five occurrences.
Dec. 22 claims 13 occurrences of the southern solstice. All of the date’s occurrences happen in the first half of the 21st century.
Dec. 21 claims most frequent status with 82 occurrences in the century, according to Coordinated Universal Time. The date opens and closes the century, with Jan. 1, 2001, and Dec. 31, 2100, occurrences, respectively. For 35 straight years, from Wednesday, Dec. 21, 2044, to Friday, Dec. 22, 2079, the date will hold exclusive claim to the December solstice.
The takeaway for the 2017 winter solstice that happens Thursday, Dec. 21, in the Northern Hemisphere at 16:29 UTC (11:29 a.m. EST) is that the Southern Hemisphere knows the astronomical event as a summer solstice.

the year’s seasonal pairings of equinoxes and solstices: Henry Kiddle’s A New Manual of the Elements of Astronomy, Descriptive and Mathematical (1877), p. 83, Public Domain, 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:
map of Earth at instant of southern solstice, Thursday, Dec. 21, at 16:29 Coordinated Universal Time (11:29 a.m. Eastern Standard Time): John Walker/Earth and Moon Viewer, Public Domain, via Fourmilab Switzerland @ https://www.fourmilab.ch/cgi-bin/Earth
the year’s seasonal pairings of equinoxes and solstices: Henry Kiddle’s A New Manual of the Elements of Astronomy, Descriptive and Mathematical (1877), p. 83, Public Domain, 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. “Everything You Need to Know: December Solstice 2016.” EarthSky > Astronomy Essentials > Earth. Dec. 15, 2016.
Available @ http://earthsky.org/?p=2951
“December Solstice 2016.” Time And Date > Time Zones > World Clock > Event Time Announcer.
Available @ https://www.timeanddate.com/worldclock/fixedtime.html?iso=20161221T1044&msg=December%20Solstice%202016
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. “Solstices and Equinoxes: 2001 to 2100 Greenwich Mean Time.” Astro Pixels > Ephemeris.
Available @ http://www.astropixels.com/ephemeris/soleq2001.html
“Event in UTC on Thursday, December 21, 2017 at 4:29:00 p.m.” Time And Date > Time Zones > World Clock > Event Time Announcer.
Available @ https://www.timeanddate.com/worldclock/fixedtime.html?iso=20171221T1629&p1=1440
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. “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. “December Solstice Brings Longest Days for Whole Earth.” EarthSky > Tonight. Dec. 21, 2016.
Available @ http://earthsky.org/tonight/longest-days-of-year-accompany-the-december-solstice
McClure, Bruce. “Shortest Season Starts at December Solstice.” EarthSky > Tonight. Dec. 16, 2016.
Available @ http://earthsky.org/tonight/years-shortest-season-starts-with-december-solstice
“Time Changes in Apia Over the Years.” Time And Date > Time Zones > World > Samoa > Apia.
Available @ https://www.timeanddate.com/time/zone/samoa/apia
"Time Zone Abbreviations - Worldwide List." Time And Date > Time Zones.
Available @ https://www.timeanddate.com/time/zones/
“Winter Solstice -- Shortest Day of the Year.” Time And Date > Sun & Moon.
Available @ http://www.timeanddate.com/calendar/winter-solstice.html

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