December Solstice Always Occurs at the Same Instant Everywhere on Earth

Summary: The December solstice, which occurs Wednesday, Dec. 21, at 10:44 Coordinated Universal Time, always occurs at the same instant everywhere on Earth.

seasonal variations; solstices signal maximum polar tipping away from or toward the sun: NASA, Public Domain, via NASA Solar System Exploration

Every year the December solstice, which takes place Wednesday, Dec. 21, 2016, at 10:44 Coordinated Universal Time (5:44 a.m. Eastern Standard Time), always occurs at the same instant everywhere on Earth.

Conversion of the instantaneous 2016 December solstice to local times in the world’s capitals yields dates ranging from Tuesday, Dec. 20, to Thursday, Dec. 22. For example, Alofi, capital of the 100-square-mile (260-square-kilometer) South Pacific island state of Niue, lies 10 degrees 5 minutes east of the date-changing International Date Line. The December solstice, which opens astronomical summer for Niue, is timed for Tuesday, Dec. 20, at 11:44 p.m. Niue Time (NUT). Niue’s time zone lags 11 hours behind UTC (UTC-11).

Apia, capital city of the Independent State of Samoa in the South Pacific Ocean, lies 8 degrees 15 minutes west of the date-changing IDL. Adjusted for summer time, which began Sunday, Sept. 25, 2016, the December solstice takes place Thursday, Dec. 22, at 12:44 a.m. West Samoa Time (WST). Samoa’s summer time zone is 14 hours ahead of UTC (UTC+14).

Wednesday dates prevail for the world’s populous capitals. The 2016 December solstice happens in Mexico City, Mexico, at 4:44 a.m. (UTC-5). Across the Atlantic Ocean, in Lisbon, Portugal, it is 10:44 a.m. (UTC+1). Across the Pacific Ocean, in Jakarta, Indonesia, it is 5:44 p.m. (UTC+7).

Earth’s time zones convert Coordinated Universal Time (UTC) to local time. UTC has been the official standard for world time since Saturday, Jan. 1, 1972. UTC starts at midnight, indicated as 0:00, and applies the 24-hour styling of military time notation for succeeding hours. For example, four and one-quarter hours after midnight, 4:14 a.m. is styled as 4:14. Noon is represented by 12:00. Mid-afternoon, at 3 p.m., is designated by 15:00. One minute before midnight, 11:59 p.m., is noted as 23:59.

The world’s time standard is linked to zero degrees longitude. The world’s present-day time zones, which are angled around internal and international borders, are calculated as hours or hours and minutes ahead of or behind UTC.

The range of times and dates for the 2016 December solstice emphasizes Earth’s inhabited vastness. Whether they note the December solstice, Earthlings, with a global population of around 7.5 billion as of October 2016, are all affected by the impact of the changing astronomical seasons upon lifestyles and life events.

Every year the December solstice opens astronomical winter in the Northern Hemisphere and astronomical summer in the Southern Hemisphere. The astronomical event triggers the Northern Hemisphere’s shortest season, shortest day and longest night as the Earth’s tilted axis increases daily hours of darkness in the Northern Hemisphere and as Earth’s somewhat elliptical orbit reaches closest approach to the sun, known as perihelion (Ancient Greek περί, perí, “near” + ἥλιος, hḗlios, “sun”).

Earth’s axis, currently tilted at 23.43711 degrees to its perpendicular orbital axis, leans away from the sun at the North Pole and toward the sun at the South Pole. The tilt that favors the Southern Hemisphere with astronomical summer precipitates astronomical winter in the Northern Hemisphere. The December solstice, known as the Northern Hemisphere’s winter solstice, marks the year’s shortest day and longest night in the Northern Hemisphere.

At the instant of the 2016 December solstice, Earth is drawing close to maximum orbital nearness to the sun. On Wednesday, Jan. 4, 2017, two weeks after the December solstice, Earth reaches perihelion.

Earth travels faster in orbital nearness to the sun and slower in orbital remoteness from the sun. The faster travel shortens the duration of the astronomical season that occurs at or near perihelion. From 1246 through 6429, winter rates as the shortest astronomical season. In 6430, when perihelion coincides with the March equinox, the Northern Hemisphere’s astronomical winter will cede the title of shortest season to astronomical spring.

The takeaway for the astronomical event variously dated as Dec. 20, 21 and 22 is that the December solstice always occurs at the same instant everywhere on Earth.

With conversions to local time via Earth’s current time zones, the December solstice always happens at the same instant everywhere on Earth: standard world time zones as of September 2016: TimeZonesBoy, CC BY SA 4.0, via Wikimedia Commons

Acknowledgment

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

Image credits:

seasonal variations; solstices signal maximum polar tipping away from or toward the sun: NASA, Public Domain, via NASA Solar System Exploration @ http://solarsystem.nasa.gov/galleries/seasonal-variations

With conversions to local time via Earth’s current time zones, the December solstice always happens at the same instant everywhere on Earth: standard world time zones as of September 2016: TimeZonesBoy, CC BY SA 4.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Standard_World_Time_Zones.png

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