Dec. 21 Solstice Opes Northern Astronomical Winter and Southern Summer

Summary: With a south polar tilt toward the sun, the Dec. 21, 2024, solstice simultaneously opes northern astronomical winter and southern astronomical summer.

winter solstice, rainbow and Castle Geyser eruption, Upper Geyser Basin, Yellowstone National Park, Teton County, Wyoming; image credit National Park Service / Jacob W. Frank: via National Park Service

With Earth's South Pole tilting toward the sun and its away-tilted North Pole, the Dec. 21, 2024, solstice simultaneously opes the astronomical seasons of winter in the Northern Hemisphere and summer in the Southern Hemisphere.

The December solstice in 2024 is scheduled for Saturday, Dec. 21, 2024, 4:21 a.m. Eastern Standard Time (EST) in the Northern Hemisphere. The Earth-wide astronomically seasonal event takes place at 09:21 Coordinated Universal Time (UTC), the Earth's primary time standard, according to the U.S. Naval Observatory, Astronomical Applications Department's "Earth Seasons -- Equinoxes and Solstices -- 2023-2026," published on the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service website. The solstice happens on Saturday, Dec. 21, for all 14 times zones (UTC+1 through UTC+14) lying east of UTC. It occurs Saturday, Dec. 21, for the first nine (UTC-1 through UTC-9) of the 12 time zones west of UTC. It takes place on Friday, Dec. 20, for the last three (UTC-10 through UTC-12) of the 12 times zones west of UTC, according to "Time Zone Converter -- Time Difference Calculator (Classic)," published on the Time and Date website.

A positive UTC offset, indicated as UTC+1 through UTC+14, references time zones east of UTC. A negative UTC offset, designated as UTC-1 through UTC-12, signifies time zones west of UTC. Time zones east of UTC are ahead of UTC. Time zones west of UTC lag behind UTC.

The December solstice complements the year's June solstice with respect to the astronomical seasons of summer and winter. The December solstice reverses the June solstice's hemispheric seasonal openings. Accordingly, the December solstice signals astronomical winter in the Northern Hemisphere and astronomical summer in the Southern Hemisphere.

The involvement of "some imaginary lines on our planet" answers the question "But what is the solstice exactly?" asked by NASA Jet Propulsion Laboratory web producer, editor and writer Jessica Stoller-Conrad in "What Is a Solstice?" on the National Oceanic and Atmospheric Administration's (NOAA) SciJinks website. Earth's axis of rotation, the equator and "special" tropical latitudinal circles of Cancer in the Northern Hemisphere and Capricorn in the Southern Hemisphere associate with the year's two solstices.

Each of the two solstices specifies its own tropical latitudinal circle. The June solstice connects with the Northern Hemisphere's Tropic of Cancer. December's solstice links with the Southern Hemisphere's Tropic of Capricorn. The sun's directly overhead placement at high noon, i.e., 12:00 p.m., characterizes each solstice's respective circle of latitude. Accordingly, the sun sits directly above the Tropic of Cancer on the June solstice and directly above the Tropic of Capricorn on the December solstice.

These two imaginary circles demarcate, respectively, the northernmost and southernmost latitudes experiencing a directly overhead sun at high noon during the sun's two annual crossings above the equator. Solstices (Latin: sol, "sun" + sistere, "to stand still") represent the stops of directly overhead placements in the sun's northward and southward equatorial crossings. "Outside the tropic zones, whether to the south or north, the sun is never directly overhead," explains Jessica Stoller-Conrad.

The year's two solstices participate in the openings of Earth's astronomical seasons with the year's two equinoxes, which occur in March and September. The March equinox announces astronomical spring in the Northern Hemisphere and astronomical autumn in the Southern Hemisphere. September's equinox introduces astronomical autumn in the Northern Hemisphere and astronomical spring in the Southern Hemisphere.

Three-month intervals distinguish the annual lineup of equinoxes and solstices. Accordingly, the year's first equinox appears in the Gregorian calendar's third month, March. Three months later, as the year's sixth month, June initiates the year's first solstice. After three months, the year's second equinox takes place in the year's ninth month, September. Three months later, as the year's 12th month, December closes the annual lineup with the year's second and final solstice.

In 2024, the schedule of the December solstice's three predecessors began with the March equinox's happening Tuesday, March 19, at 11:06 p.m. Eastern Daylight Time (EDT) and Wednesday, March 20, at 03:06 UTC. March's successor, the June solstice, took place Thursday, June 20, at 4:51 p.m. EDT and at 20:51 UTC. September's equinox occurred Sunday, Sep. 22, at 8:44 a.m. EDT and at 12:44 UTC.

full disk geocolor image of Earth captured by NOAA's GOES (Geostationary Operational Environmental Satellites)-East geostationary satellite, also known as GOES-16, at the beginning of astronomical winter, Dec. 21, 2017, at 11:28 a.m. EST (16:28 UTC): NOAA Satellites (NOAASatellites), Public Domain, via Flickr

Acknowledgment

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

Dedication

This post is dedicated to the memory of our beloved blue-eyed brother, Charles, who guided the creation of the Met Opera and Astronomy posts on Earth and Space News. We memorialized our brother in "Our Beloved Blue-Eyed Brother, Charles, With Whom We Are Well Pleased," published on Earth and Space News on Thursday, Nov. 18, 2021, an anniversary of our beloved father's death.

Image credits:

winter solstice, rainbow and Castle Geyser eruption, Upper Geyser Basin, Yellowstone National Park, Teton County, Wyoming; image credit National Park Service / Jacob W. Frank: via National Park Service @ https://www.nps.gov/subjects/naturalphenomena/winter-solstice.htm

full disk geocolor image of Earth captured by NOAA's GOES (Geostationary Operational Environmental Satellites)-East geostationary satellite, also known as GOES-16, at the beginning of astronomical winter, Dec. 21, 2017, at 11:28 a.m. EST (16:28 UTC): NOAA Satellites (NOAASatellites), Public Domain, via Flickr @ https://www.flickr.com/photos/noaasatellites/27423141859

For further information:

Marriner, Derdriu. "2017 Winter Solstice Happens Thursday, Dec. 21, in Northern Hemisphere." Earth and Space News. Wednesday, Dec. 20, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/12/2017-winter-solstice-happens-thursday.html

Marriner, Derdriu. "2018 Winter Solstice Happens Friday, Dec. 21, in Northern Hemisphere." Earth and Space News. Wednesday, Dec. 19, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/12/2018-winter-solstice-happens-friday-dec.html

Marriner, Derdriu. "2019 Winter Solstice Happens Sunday, Dec. 22, in Northern Hemisphere." Earth and Space News. Wednesday, Dec. 11, 2019.
Available @ https://earth-and-space-news.blogspot.com/2019/12/2019-winter-solstice-happens-sunday-dec.html

Marriner, Derdriu. "American Samoa Has Summer Solstice As Rest of U.S. Has Winter Solstice." Earth and Space News. Wednesday, Dec. 12, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/12/american-samoa-has-summer-solstice-as.html

Marriner, Derdriu. "December Signals Summer Solstice for American Samoa and Jarvis Island." Earth and Space News. Wednesday, Dec. 18, 2019.
Available @ https://earth-and-space-news.blogspot.com/2019/12/december-signals-summer-solstice-for.html

Marriner, Derdriu. "Wednesday, November 30, 2016 December Solstice Always Occurs at the Same Instant Everywhere on Earth." Earth and Space News. Wednesday, Nov. 30, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/11/december-solstice-always-occurs-at-same.html

Marriner, Derdriu. "December Solstice Opens Astronomical Winter With 2016’s Longest Night." Earth and Space News. Wednesday, Dec. 14, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/12/december-solstice-opens-astronomical.html

Marriner, Derdriu. "December Winter Solstice Opens Northern Hemisphere’s Shortest Season." Earth and Space News. Wednesday, Dec. 21, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/12/december-winter-solstice-opens-northern.html

Marriner, Derdriu. "Northern Latitudes Have Least Amount of Daylight Near December Solstice." Earth and Space News. Wednesday, Dec. 4, 2019.
Available @ https://earth-and-space-news.blogspot.com/2019/12/northern-latitudes-have-least-amount-of.html

Marriner, Derdriu. "Two Weeks After 2016 December Solstice Earth Reaches 2017 Perihelion." Earth and Space News. Wednesday, Dec. 28, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/12/two-weeks-after-2016-december-solstice.html

Marriner, Derdriu. "Two Weeks After the 2018 December Solstice Earth Reaches Perihelion." Earth and Space News. Wednesday, Dec. 26, 2018.
Available @ https://earth-and-space-news.blogspot.com/2018/12/two-weeks-after-2018-december-solstice.html

National Park Service. "Winter Solstice." National Park Service > Natural Phenomena. Last updated Dec. 24, 2022.
Available via National Park Service @ https://www.nps.gov/subjects/naturalphenomena/winter-solstice.htm

Stoller-Conrad, Jessica. "What Is a Solstice?" NOAA SciJinks > Topics > Weather Forecasting. Updated Oct. 3, 2023.
Available via NOAA SciJinks @ https://scijinks.gov/solstice/

Stoller-Conrad, Jessica. "Why Does Earth Have Seasons?" NOAA SciJinks > Topics > Weather Forecasting. Updated Oct. 3, 2023.
Available via NOAA SciJinks @ https://scijinks.gov/earths-seasons/

U.S. Naval Observatory, Astronomical Applications Department. "Earth Seasons -- Equinoxes and Solstices -- 2023-2026." NOAA National Weather Service.
Available via NOAA National Weather Service @ https://www.weather.gov/media/ind/seasons.pdf