2017 Spring Equinox Happens Monday, March 20, in Northern Hemisphere

Summary: The 2017 spring equinox, which opens the Northern Hemisphere’s astronomical spring, happens Monday, March 20, at 10:29 Coordinated Universal Time (UTC).

time zone map: MrMingsz at English Wikipedia, Public Domain, via Wikimedia Commons

The 2017 spring equinox, which opens astronomical spring in the Northern Hemisphere, happens Monday, March 20, at 10:29 Coordinated Universal Time (UTC).

Also known as the March equinox, the astronomical event opens the Northern Hemisphere’s astronomical spring and the Southern Hemisphere’s astronomical autumn. The seasonal opposition of the two hemispheres explains the recognition of the March equinox as the autumnal equinox in the Southern Hemisphere.

The date of the March equinox exhibits annual variations. The March equinox may take place on March 19, March 20 or March 21, according to Coordinated Universal Time, the world’s official time standard. In the 21st century, which spans Jan. 1, 2001, to Dec. 31, 2100, Coordinated Universal Time claims March 20 as the most common date for the Northern Hemisphere’s spring equinox and the Southern Hemisphere’s autumnal equinox. March 20 makes 78 appearances. March 19 occupies second place, with 20 occurrences.

March 21 claims the 21st century’s lowest frequency, with only two occurrences. Both instances occur in the century’s first decade.

March 20 claims the 21st century’s opening and closing equinoxes in 2001 and 2100, respectively. The prevalence of March 20 in the first five decades of the 21st century signals the date’s centurial dominance. The equinox falls exclusively on March 20 from 2008 through 2043.

March 19 breaks March 20’s 3.6 decade-long run in 2044. March 20 reclaims the equinox in 2045, has a brief replacement by March 19 in 2048, and then resumes occurrence in the last two years of the fifth decade.

The second half of the 21st century is speckled with March 19 occurrences. The date claims 36 percent, with 18 occurrences, of the century’s last 50 March equinoxes.

Time zone differences account for an observational range of the March equinox encompassing the day before or the day after each year’s official date. In the 48 states of the continental United States, the northern spring equinox happens Monday, March 20. Times range from 3:29 a.m. Pacific Daylight Time (PDT) to 6:29 a.m. Eastern Daylight Time (EDT). For the United States’ two non-contiguous states, the equinox still takes place on Monday. Alaska Daylight Time (AKDT) clocks the northern spring equinox Monday morning, at 2:29 a.m. Hawaii-Aleutian Daylight Time (HADT) places the time at 12:29 a.m.

Time zones that lag more than 10 hours behind UTC have a date of March 19 for the 2017 equinox. The Territory of American Samoa, an unincorporated U.S. territory in the South Pacific Ocean, welcomes the equinox on Sunday, March 19, at 11:29 p.m. Samoa Standard Time (SST). Samoa’s time zone, which is 11 hours behind Coordinated Universal Time, is represented as UTC - 11. Also, because the archipelago of five main islands and two coral atolls is one of only two U.S. possessions located in the Southern Hemisphere, American Samoa experiences the event as an autumnal, not a vernal, equinox.

The highest time zone, which adds 14 hours to UTC (UTC + 14), always claims the privilege of being the first to welcome a new day and, therefore, also the first to greet a new year. When an event happens mid-morning, at 10 a.m. UTC, the highest time zone experiences the event as the next day.

Located northwest of American Samoa, the Independent State of Samoa (Malo Sa 'oloto Tuto 'atasi o Sāmoa) is on daylight savings in its West Samoa time zone (WST) at the time of the March 2017 equinox. Samoa's offset of Coordinated Universal Time during daylight savings, which is expressed as UTC + 14, places the South Pacific archipelago of two main islands and four smaller islands in the highest time zone. West Samoa Time clocks 2017's first equinox 25 hours after its southeastern neighbor, at 12:29 a.m., Tuesday, March 21. Samoa, however, joins its Southern Hemisphere neighbor in observing the event as the autumn equinox, the astronomical opener of autumn.

The takeaway for the 2017 spring equinox is that it happens, according to Coordinated Universal Time, Monday, March 20, as a spring equinox in the Northern Hemisphere and as an autumnal equinox in the Southern Hemisphere.

Relationships between such factors as Earth's rotational axis, Earth's rotational axial tilt, the celestial equator and the ecliptical explain the twice yearly astronomical events of equinoxes: Dennis Nilsson (Dna-Webmaster), CC BY 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:

time zone map: MrMingsz at English Wikipedia, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Timezones_UTC%2B14.png

Relationships between such factors as Earth's rotational axis, Earth's rotational axial tilt, the celestial equator and the ecliptical explain the twice yearly astronomical events of equinoxes: Dennis Nilsson (Dna-Webmaster), CC BY 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:AxialTiltObliquity.png

For further information:

“10 Things About the March Equinox.” Time And Date > Sun & Moon.
Available @ https://www.timeanddate.com/calendar/ten-things-march-equinox.html

“Equinox: Equal Day and Night, Almost.” Time And Date > Sun & Moon.
Available @ https://www.timeanddate.com/astronomy/equinox-not-equal.html

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

“March Equinox - Equal Day and Night, Nearly.” Time And Date > Sun & Moon.
Available @ https://www.timeanddate.com/calendar/march-equinox.html

Marriner, Derdriu. “First Point of Aries for Spring Equinox Actually Happens in Pisces.” Earth and Space News. Wednesday, March 8, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/03/first-point-of-aries-for-spring-equinox.html

“Spring Equinox - Vernal Equinox.” Time And Date > Sun & Moon.
Available @ https://www.timeanddate.com/calendar/spring-equinox.html