American Samoa Has Autumn Equinox While United States Has Spring Equinox

Summary: American Samoa, one of only two US possessions in the Southern Hemisphere, has an autumn equinox while most of the United States has a spring equinox.

(left) Tutuila, largest island of American Samoa, imaged February 2000 by NASA Space Shuttle Endeavour’s Shuttle Radar Topography Mission: NASA/JPL ()/NGA, Public Domain, via NASA Jet Propulsion Laboratory Photojournal
(right) Jarvis Island, April 4, 2007: NASA Gateway to Astronaut Photography of Earth, Public Domain, via NASA JSC EOL (Earth Observing Laboratory)

Along with uninhabited Jarvis Island, the United States' only other possession in the Southern Hemisphere, American Samoa has an autumn equinox while the United States has a spring equinox.

The simultaneous experience of the March 2017 equinox as an autumn equinox by American Samoa and Jarvis Island in the Southern Hemisphere but as a spring equinox by the rest of the United States exemplifies the opposition of the seasons between the two hemispheres. The southerly locations of American Samoa and Jarvis Island, both sited south of the equator in the South Pacific Ocean, qualify them for experiencing the Southern Hemisphere’s seasonal progression.

The annual March equinox opens astronomical spring in the Northern Hemisphere and astronomical autumn in the Southern Hemisphere. In this way, the March equinox is known as a spring equinox in the Northern Hemisphere and as an autumn equinox in the Southern Hemisphere.

The March 2017 equinox happens Monday, March 20, at 10:29 Coordinated Universal Time (UTC), the world’s official time standard. Except for American Samoa, the equinox also takes place Monday, March 20, throughout the rest of the United States.

American Samoa operates under Samoa Standard Time (SST). The South Pacific Ocean archipelago of five main islands and two coral atolls does not observe daylight savings time, so no seasonal time changes take place.

Samoa Standard Time sets the March 2017 equinox a day earlier than the rest of the United States. American Samoa’s autumn equinox happens Sunday, March 19, at 11:29 p.m. American Samoa’s experience of the March 2017 equinox, then, also precedes the astronomical event’s occurrence according to the world’s official time standard. Lagging 11 hours behind UTC, Samoa Standard Time is represented as UTC – 11.

American Samoa covers more than 300 miles (482.8 kilometers) in its east to west stretch across the South Pacific Ocean. The U.S. possession roughly spans 11 to 15 degrees south latitude and 168 to 171 degrees west longitude.

American Samoa belongs to the Samoan archipelago, which hosts the Independent State of Samoa (Malo Sa 'oloto Tuto 'atasi o Sāmoa), formerly known as West Samoa. The International Date Line separates the two Samoas. American Samoa is just east of the imaginary line of longitude while Samoa is to the west.

The unincorporated U.S. territory lies 2,600 miles (4,184.29 kilometers) southwest of the United States’ mid-North Pacific Ocean state, Hawaii. New Zealand is located 1,800 miles (2,896.81 kilometers) to the southeast. French Polynesia dots the South Pacific Ocean over 1,500 miles (2,414 kilometers) to the east of American Samoa.

Jarvis Island, the United States’ other possession in the Southern Hemisphere, lies northeast of American Samoa. The uninhabited, small island of only 1.73 square miles (4.5 square kilometers) hugs the equator from a distance of only 22 nautical miles (25.31 miles; 40.74 kilometers). The U.S. Fish and Wildlife Service (USFWS) administers Jarvis Island as a National Wildlife Refuge, with public access by permit only and mostly restricted to educators and scientists.

The Central Intelligence Agency’s Map of Standard Time Zones of the World, as of October 2015, gives Jarvis Island an offset of 11 hours behind Coordinated Universal Time, expressed as UTC – 11. According to the CIA’s map, Jarvis Island shares the same date and time of occurrence of the March 2017 equinox with American Samoa. Both of the United States’ South Pacific Ocean possessions observe their autumnal equinox Sunday, March 19, at 11:29 p.m.

The takeaway for the flipped seasons between Earth’s Northern Hemisphere and Southern Hemisphere is that the United States’ two Southern Hemisphere possessions, American Samoa and Jarvis Island, experience the March 2017 equinox as an autumn equinox while the rest of the United States has a spring equinox.

International Date Line, with the United States' only two Southern Hemisphere possessions, American Samoa and Jarvis Island (center): CC BY SA 3.0, 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:

(left) Tutuila, largest island of American Samoa, imaged February 2000 by NASA Space Shuttle Endeavour’s Shuttle Radar Topography Mission: NASA/JPL/NGA, Public Domain, via NASA Jet Propulsion Laboratory Photojournal @ http://photojournal.jpl.nasa.gov/catalog/PIA11965
(right) Jarvis Island, April 4, 2007: NASA Gateway to Astronaut Photography of Earth, Public Domain, via NASA JSC EOL (Earth Observing Laboratory) @ https://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=ISS014&roll=E&frame=18970

International Date Line, with the United States' only two Southern Hemisphere possessions, American Samoa and Jarvis Island (center): CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:International_Date_Line.png

For further information:

“How Far Is Jarvis Island From the Equator?” University of Hawai’i at Manoa’s SOEST (School of Ocean and Earth Science and Technology) > Jarvis Island Information > Equator.
Available @ http://www.jarvisisland.info/equator.html

“Islands in the Pacific Ocean - Jarvis, Baker, and Howland Islands.” NOAA (National Oceanic and Atmospheric Administration) Charts > Booklet Chart™.
Available @ http://www.charts.noaa.gov/BookletChart/83116_BookletChart.pdf

“National Park of American Samoa.” National Park Service > National Park of American Samoa > Plan Your Visit > Maps.
Available @ https://www.nps.gov/npsa/planyourvisit/maps.htm

“PRIA: Jarvis Island.” Pacific Islands Benthic Habitat Mapping Center > Pacific Remote Island Area (PRIA).
Available @ http://www.soest.hawaii.edu/pibhmc/pibhmc_pria_jar.htm