2019 September Equinox Happens Sunday, Sept. 22, or Monday, Sept. 23

Summary: The 2019 September equinox happens Sunday, Sept. 22, or Monday, Sept. 23, according to local time zone conversions of Coordinated Universal Time.

view of the 2017 September equinox from NOAA’s GOES (Geostationary Satellite Server)-16 satellite: NOAA Satellite and Information Service @NOAASatellites/Facebook Sept. 22, 2017, Public Domain, via Wikimedia Commons

The 2019 September equinox happens Sunday, Sept. 22, or Monday, Sept. 23, with the date range reflecting local time zone conversions of Coordinated Universal Time (UTC), the world’s primary time standard.

Coordinated Universal Time places the instant of the 2019 September equinox at 07:50, Monday, Sept. 23. UTC is the timescale observed by the U.S. Naval Observatory in Washington, D.C. The International Bureau of Weights and Measures (Bureau International des Poids et Mesures [BIPM]) is charged with maintaining UTC. BIPM is headquartered in Sèvres, southwestern Paris, north central France.

The world’s time zones convert UTC into local time. Negative and positive offsets express the differences between local time and UTC. Time zones east of the prime meridian (0 degrees longitude) have positive offsets to express time later than UTC. Time zones west of the prime meridian have negative offsets to designate time earlier than UTC.

The prime meridian pairs with the International Date Line (IDL). The dateline stretches across Earth’s surface as an imaginary line connecting the North Pole and the South Line. The IDL is considered as a line of demarcation that distinguishes the Eastern and Western Hemispheres.

The International Date Line also demarcates the date change between east and west. Passing from east to west across the IDL adds a day. A west-to-east transit across the IDL subtracts a day.

The date change in crossing the International Date Line does not necessarily amount to 24 hours. Time And Date website gives the example of traveling 1,061 kilometers (659 miles) across the IDL from the U.S. equatorial Pacific Ocean territory of Baker Island to New Zealand’s dependent territory of Tokelau requires the addition of 25 hours (1 day 1 hour).

Baker Island’s offset of UTC-12 indicates that the coral island’s time zone lags behind Coordinated Universal Time by 12 hours. Baker Island places the instant of the 2019 September equinox at 7:50 p.m. Sunday, Sept. 22.

Tokelau’s offset of UTC+13 reveals that three-island archipelago’s time zone is 13 hours later than UTC. The instant of the 2019 September equinox happens Monday, Sept. 23, at 8:50 p.m. Tokelau Time (TKT).

The U.S. Central Intelligence Agency’s (CIA) geographic coordinates for Baker Island are 0 degrees 13 minutes north latitude, 176 degrees 28 minutes west longitude. On the other side of the International Date Line, Tokelau’s CIA geographic coordinates are 9 degrees south latitude, 172 degrees west longitude.

Baker Island and Tokelau lie on opposite sides of the equator. Baker Island occupies the Northern Hemisphere, albeit less than one-fifth of a degree north of the equator. The Southern Hemisphere claims Tokelau, which is nine degrees south of the equator.

As a Northern Hemisphere occupant, Baker Island experiences the September equinox as an autumn equinox. As a Southern Hemisphere dweller, Tokelau welcomes the September equinox as a spring equinox.

The September equinox occurs as the second of two annual equinoxes. The year’s first equinox happens in March. Both equinoxes open opposite seasons in the Northern and Southern Hemispheres. The March equinox announces astronomical spring in the Northern Hemisphere and astronomical autumn in the Southern Hemisphere.

The yearly equinoxes associate with the perpendicular angle of Earth’s axis to Earth’s orbital plane around the sun. The axial-orbital perpendicularity accounts for equal illumination of both the Northern Hemisphere and the Southern Hemisphere by the sun’s rays. The designation of equinox (Latin: aequus, “equal” + nox, “night”) for the biannual astronomical event references the axial-orbital perpendicularity.

The annual equinoxes pair with annual solstices as astronomical seasonal events on Earth. The year’s two solstices take place in June and in December. The June solstice’s north polar tilt toward the sun marks astronomical summer in the Northern Hemisphere and astronomical winter in the Southern Hemisphere. The December solstice’s north polar tilt away from the sun initiates astronomical winter in the Northern Hemisphere and astronomical summer in the Southern Hemisphere.

The takeaway for the 2019 September equinox, which happens Sunday, Sept. 22, or Monday, Sept. 23, is that the year’s second equinox flips the March equinox’s seasons by opening the Northern Hemisphere’s astronomical autumn and the Southern Hemisphere’s astronomical spring.

woodcut illustration of equinoxes in Cosmographia (1600) by German cartographer and cosmographer Sebastian Münster (Jan. 20, 1488-May 26, 1552): Columbia University ITC, Public Domain, 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:

view of the 2017 September equinox from NOAA’s GOES (Geostationary Satellite Server)-16 satellite: NOAA Satellite and Information Service @NOAASatellites/Facebook Sept. 22, 2017, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:View_of_the_autumnal_equinox_from_GOES_16.jpg

woodcut illustration of equinoxes in Cosmographia (1600) by German cartographer and cosmographer Sebastian Münster (Jan. 20, 1488-May 26, 1552): Columbia University ITC, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Equinoxes_(2).jpg

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. “2016 Northern Autumnal Equinox Happens Thursday, Sept. 22.” Earth and Space News. Wednesday, Sept. 21, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/09/2016-northern-autumnal-equinox-happens.html

Marriner, Derdriu. “2017 Autumn Equinox Happens Friday, Sept. 22, in Northern Hemisphere.” Earth and Space News. Wednesday, Sept. 20, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/09/2017-autumn-equinox-happens-friday-sept.html

Marriner, Derdriu. “2018 Autumn Equinox Happens Sunday, Sept. 23, in Northern Hemisphere.” Earth and Space News. Wednesday, Sept. 19, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/09/2018-autumn-equinox-happens-sunday-sept.html

NOAA Satellite and Information Service @NOAASatellites. “Happy #FirstDayofFall & #FullDiskFriday! Enjoy this view of the autumnal #equinox from NOAA’s #GOES16 satellite!” Facebook. Sept. 22, 2017.
Available @ https://www.facebook.com/NOAASatellites/photos/a.230712210302397.59001.226849284022023/1792690767437859/

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

U.S.N.O. Astronomical Applications Department. “Universal Time.” U.S. Naval Observatory Astronomical Applications Department >Astronomical Information Center > Time > Universal Time and Greenwich Mean Time.
Available @ http://aa.usno.navy.mil/faq/docs/UT.php