September Signals Spring Equinox for American Samoa and Jarvis Island

Summary: September signals a spring equinox for American Samoa and Jarvis Island but an autumn equinox for the rest of the United States.

American Samoa is one of only two U.S. possessions lying in the Southern Hemisphere; mountainous surround of Pago Pago harbor, Tutuila, American Samoa; February 2009 photo by Dr. Matt Kendall, NOAA (National Oceanic and Atmospheric Administration/NOS/NCCOS/CCMA/BGB: NOAA Photo Library, CC BY 2.0 Generic, via Flickr

September signals a spring equinox for American Samoa and Jarvis Island, as the only two U.S. possessions in the Southern Hemisphere, but an autumn equinox for the rest of the United States, as Northern Hemisphere occupiers.

The 2019 September equinox occurs Monday, Sept. 23, at 07:50 (7:50 a.m.), according to Coordinated Universal Time (UTC). Coordinated Universal Time functions as the world’s primary time standard.

The world’s time zones relate to Coordinated Universal Time as negative and positive offsets. Time zones that are east of the prime meridian, 0 degrees longitude, use positive offsets indicating time ahead of UTC. Time zones that are west of the prime meridian use negative offsets indicating time behind UTC.

American Samoa and Jarvis Island are located in the Southern Hemisphere. Both U.S. territories lie south of the equator in the South Pacific Ocean.

The U.S. Central Intelligence Agency (CIA) assigns geographic coordinates of 14 degrees 20 minutes south latitude, 170 degrees west longitude to American Samoa. Jarvis Island’s CIA geographic coordinates are listed at 0 degrees 22 minutes south latitude, 160 degrees 1 minute west longitude.

The two United States’ Southern Hemisphere territories share the same offset, UTC-11. Jarvis Island’s time zone and Samoa Standard Time (SST) zone lag behind Coordinated Universal Time by 11 hours.

American Samoa and Jarvis Island experience the instant of the 2019 September equinox Sunday, Sept. 22, at 8:50 p.m. local time. The September equinox announces astronomical spring for American Samoa and Jarvis Island. Meanwhile, the September equinox opens astronomical autumn for the rest of the United States, as Northern Hemisphere occupants.

Including American Samoa and Jarvis Island, 11 U.S. territories are located in the Pacific Ocean. Nine lie north of the equator. The Northern Hemisphere’s U.S. Pacific Ocean territories comprise two permanently inhabited territories (Guam, the Commonwealth of the Northern Mariana Islands) and seven territories without native or permanent populations. The Northern Hemisphere’s seven uninhabited U.S. Pacific Ocean territories are Baker Island, Howland Island, Johnston Atoll, Kingman Reef, Midway Atoll, Palmyra Atoll and Wake Island.

The September equinox pairs annually with its counterpart, the March equinox. The annual March equinox marks astronomical spring in the Northern Hemisphere and astronomical autumn in the Southern Hemisphere.

The equinoxes capture the points of perpendicularity in the angle formed by Earth’s rotational axis with the plane of Earth’s orbit around the sun. The lack of axial tilt away or toward the sun explains the equal receipt of the sun’s rays by Earth’s Northern Hemisphere and Southern Hemisphere at the instants of the March and September equinoxes (Latin: aequus, “equal” + nox, “night”).

The June and December solstices join the March and September equinoxes as announcers of Earth’s astronomical seasons. The June and December solstices concern the astronomical opening of summer and winter.

The June solstice signals astronomical summer in the Northern Hemisphere and astronomical winter in the Southern Hemisphere. The favoring of the Northern Hemisphere by Earth’s tilted rotational axis occasions the Northern Hemisphere’s experience of the June solstice as astronomical summer. The north polar terminus of Earth’s axis tilts toward the sun while the south polar terminus tilts away from the sun.

Contrastingly, December’s solstice initiates the Northern Hemisphere’s astronomical winter and the Southern Hemisphere’s astronomical summer. The favoring of the Southern Hemisphere by Earth’s tilted rotational axis induces the start of the hemisphere’s astronomical summer. The south polar terminus of Earth’s axis tilts toward the sun while the north polar terminus tilts away from the sun.

The takeaway for the September signal of the spring equinox for American Samoa and Jarvis Island is that the rest of the United States, as Northern Hemisphere occupants, experiences seasons oppositely from American Samoa and Jarvis Island, as Southern Hemisphere occupiers.

The U.S. Pacific Ocean territory of Jarvis Island joins American Samoa as only two U.S. possessions with opposite seasons from the rest of the United States; blue noddy (Procelsterna cerulea) at Jarvis Island: U.S. Fish & Wildlife Service, Public Domain, via USFWS Jarvis Island National Wildlife Refuge

Acknowledgment

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

Image credits:

American Samoa is one of only two U.S. possessions lying in the Southern Hemisphere; mountainous surround of Pago Pago harbor, Tutuila, American Samoa; February 2009 photo by Dr. Matt Kendall, NOAA (National Oceanic and Atmospheric Administration/NOS (National Ocean Service)/NCCOS (National Centers for Coastal Ocean Science)/CCMA (Center for Coastal Monitoring and Assessment)/BGB: NOAA Photo Library, CC BY 2.0 Generic, via Flickr @ https://www.flickr.com/photos/51647007@N08/5123384618/

The U.S. Pacific Ocean territory of Jarvis Island joins American Samoa as only two U.S. possessions with opposite seasons from the rest of the United States; blue noddy (Procelsterna cerulea) at Jarvis Island: U.S. Fish & Wildlife Service, Public Domain, via USFWS Jarvis Island National Wildlife Refuge @ https://www.fws.gov/refuge/jarvis_island/wildlife_and_habitat/blue_noddy.html

For further information:

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

Marriner, Derdriu. “2019 September Equinox Happens Sunday, Sept. 22, 0r Monday, Sept. 23.” Earth and Space News. Wednesday, Sept. 11, 2019.
Available @ https://earth-and-space-news.blogspot.com/2019/09/2019-september-equinox-happens-sunday.html

Marriner, Derdriu. “American Samoa Has Autumn Equinox While United States Has Spring Equinox.” Earth and Space News. Wednesday, March 1, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/03/american-samoa-has-autumn-equinox-while.html

Marriner, Derdriu. “March Signals Autumn Equinox for American Samoa and Jarvis Island.” Earth and Space News. Wednesday, March 20, 2019.
Available @ https://earth-and-space-news.blogspot.com/2019/03/march-signals-autumn-equinox-for.html

U.S. Central Intelligence Agency. “Field Listing: Geographic Coordinates.” Central Intelligence Agency > Library > Publications > The World Factbook.
Available @ https://www.cia.gov/library/publications/the-world-factbook/fields/2011.html

U.S. Central Intelligence Agency. “Standard Time Zones of the World, May 2018.” Central Intelligence Agency > Library > Publications > The World Factbook.
Available @ https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf

U.S.N.O. Astronomical Applications Department. “Equinox.” U.S. Naval Observatory Astronomical Applications Department > Information Center > Terms Used on This Website > The Astronomical Almanac Online.
Available @ http://asa.usno.navy.mil/SecM/Glossary.html#_E

U.S.N.O. Astronomical Applications Department. “Equinoxes.” U.S. Naval Observatory Astronomical Applications Department > Information Center > Phenomena of the Sun and Moon > Length of Day and Night at the Equinoxes.
Available @ http://aa.usno.navy.mil/faq/docs/equinoxes.php