2018 Northern Hemisphere Spring Equinox Happens Tuesday, March 20

Summary: The 2018 Northern Hemisphere spring equinox happens Tuesday, March 20, at 16:15 Coordinated Universal Time (12:15 p.m. Eastern Daylight Time).

map of Earth at instant of 2018 northern spring equinox, Tuesday, March 20, at 16:15 Coordinated Universal Time (12:15 p.m. Eastern Daylight Time): John Walker/Earth and Moon Viewer, Public Domain, via Fourmilab Switzerland

The 2018 Northern Hemisphere spring equinox happens Tuesday, March 20, at 16:15 Coordinated Universal Time (12:15 p.m. Eastern Daylight Time), as an astronomical event marking the transition from northern astronomical winter to northern astronomical spring.

The March equinox announces astronomical autumn in the Southern Hemisphere. The March equinox is known as the vernal (Latin: vernalis, “of or pertaining to spring”) equinox in the Northern Hemisphere and as the autumnal equinox in the Southern Hemisphere.

The March equinox marks the sun’s apparent south-to-north crossing of the imaginary celestial equator into the imaginary celestial sphere’s Northern Hemisphere. The March equinox’s opposite occurs annually in September. The September equinox pinpoints the sun’s apparent north-to-south crossing of the celestial equator into the celestial sphere’s Southern Hemisphere. The September equinox is known as the autumnal equinox in the Northern Hemisphere and as the vernal, or spring, equinox in the Southern Hemisphere.

EarthSky Tonight lead writer Bruce McClure explains that, although the celestial equator and the celestial sphere are imaginary, events such as equinoxes are real. The use of these imaginary components, which is known as spherical or positional astronomy, dates back to antiquity. The celestial sphere, which is concentric to Earth, allows for determining the locations of objects in the sky by observers at a particular date, time and place on Earth.

The term of equinox (Latin: aequus, “equal” + nox, “night”) for the March and September astronomical events recognizes the almost equal solar illumination of the Northern and Southern Hemispheres. The approximately equal illuminations translates as an approximately equal length of daytime and nighttime.

At the time of each equinox, the tilt of Earth’s axis is perpendicular to the sun. The equinox sun appears exactly overhead at Earth’s equator.

In terms of the imaginary celestial sphere, the equinox sun’s location is on the celestial equator. The intersection of the observer’s horizon with the celestial equator serves as an indicator of due east and due west. Except at the North and South Poles, everywhere on Earth experiences the equinox sun’s due east rising and due west setting.

The 2018 March equinox takes place during the year’s second blue moon month. A blue moon’s designation derives from a full moon’s calendrical or seasonal occurrence. A calendrical blue moon occurs as the second of two full moons within the same month. A seasonal blue moon represents the third of four full moons within the same seasons.

Both of 2018’s blue moons qualify as calendrical blue moons. The year’s first blue moon happened Wednesday, Jan. 31, at 13:27 p.m. UTC (8:27 a.m. Eastern Standard Time). January’s first full moon occurred Tuesday, Jan. 2, at 02:24 UTC (Monday, Jan. 1, at 9:24 p.m. EST).

March 2018’s first full moon appeared Friday, March 2, at 00:51 UTC (Thursday, March 1, at 7:51 p.m. EST). The month’s blue, or second full, moon occurs Saturday, March 31, at 12:37 UTC (8:37 a.m. EDT).

After the March equinox, the year’s next astronomical seasonal event is the June solstice. The June solstice is known as the summer solstice in the Northern Hemisphere and as the winter solstice in the Southern Hemisphere. The 2018 June solstice takes place Thursday, June 21, at 10:07 UTC (6:07 a.m. EDT).

The March equinox’s opposite takes place in September as marker of northern autumn and southern spring. The September equinox occurs Sunday, Sept. 23, at 01:54 UTC (Saturday, Sept. 22, at 9:54 p.m. EDT).

The year’s final astronomical seasonal event occurs as the December solstice. The December solstice is known as the winter solstice in the Northern Hemisphere and as the summer solstice in the Southern Hemisphere. The 2018 December solstice happens Friday, Dec. 21, at 22:22 UTC (5:22 p.m. EST).

The takeaways for the 2018 Northern Hemisphere spring equinox happening Tuesday, March 20, at 16:15 UTC (12:15 p.m. EDT), are that the March equinox opens the year’s quartet of astronomical seasonal events and shares its month with 2018’s second blue moon.

every hour of equinox sun’s day arc, as seen on the celestial dome from the pole: Tau’olunga, 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:

map of Earth at instant of 2018 northern spring equinox, Tuesday, March 20, at 16:15 Coordinated Universal Time (12:15 p.m. Eastern Daylight Time): John Walker/Earth and Moon Viewer, Public Domain, via Fourmilab Switzerland @ http://www.fourmilab.ch/cgi-bin/Earth

every hour of equinox sun’s day arc, as seen on the celestial dome from the pole: Tau’olunga, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Equinox-90.jpg

For further information:

Espenak, Fred. “2018 Calendar of Astronomical Events Greenwich Mean Time.” Astro Pixels > Ephemeris.
Available @ http://astropixels.com/ephemeris/astrocal/astrocal2018gmt.html

Espenak, Fred. “Phases of the Moon: 2001 to 2100 Universal Time.” Astro Pixels > Ephemeris > Moon.
Available @ http://www.astropixels.com/ephemeris/phasescat/phases2001.html

Gaherty, Geoff. “Equinox Explained: Why Earth’s Seasons Will Change on Sunday.” Space.com > Skywatchng. Sept. 18, 2013.
Available @ https://www.space.com/22852-fall-equinox-earth-seasons-explained.html

Marriner, Derdriu. “2017 Spring Equinox Happens Monday, March 20, in Northern Hemisphere.” Earth and Space News. Wednesday, March 15, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/03/2017-spring-equinox-happens-monday.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. “First March Full Moon Friday, March 2, Opens Second 2018 Blue Moon Month.” Earth and Space News. Wednesday, Feb. 28, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/02/first-march-full-moon-friday-march-2.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

McClure, Bruce. “Equinox Sun Rises Due East, Sets Due West.” EarthSky > Tonight. March 20, 2018.
Available @ http://earthsky.org/tonight/equinox-sun-rises-due-east-and-sets-due-west

“The Seasons and the Earth’s Orbit: Milankovitch Cycles.” U.S. Naval Observatory > Astronomical Applications Department.
Available @ http://aa.usno.navy.mil/faq/docs/seasons_orbit.php