Sep. 22 Equinox Opens Astronomical Fall in North and Spring in South

Summary: The Sunday, Sep. 22, 2024, equinox opens astronomical autumn in the Northern Hemisphere and astronomical spring in the Southern Hemisphere.

graphic of astronomical and meteorological seasons in 2022 in the Southern Hemisphere during Earth's orbit around the sun; image credit NOAA Office of Education/Kaleigh Ballantine: via NOAA Office of Education

The Sunday, Sep. 22, 2024, equinox opens astronomical autumn in the Northern Hemisphere and astronomical spring in the Southern Hemisphere as the second of the year's two equinoxes.

The September 2024 equinox takes place Sunday, Sep. 22, at 8:44 a.m. Eastern Daylight Time in the Northern Hemisphere. The time of the Earth-wide event at 12:44 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 equinox occurs on Sunday, Sep. 22, for the first 11 (UTC+1 through UTC+11) of the 14 time zones that lie east of UTC. The equinox happens on Monday, Sep. 23, for the last three (UTC+12 through UTC+14) time zones east of UTC. The equinox occurs on Sunday, Sep. 22, for all 12 (UTC-1 through UTC-12) time zones west of UTC, according to "Time Zone Converter -- Time Difference Calculator (Classic)," published on the Time and Date website.

A positive UTC offset, symbolized as UTC+1 through UTC+14, designates time zones east of UTC. A negative UTC offset, expressed as UTC-1 through UTC-12, indicates time zones that lie west of UTC. Time zones east of UTC are ahead of UTC. Time zones west of UTC lag behind UTC.

September's equinox functions as the announcer of astronomical autumn in the Northern Hemisphere. For the Southern Hemisphere, which experiences seasons oppositely from the Northern, September's equinox occurs as the opener of astronomical spring.

September's equinox pairs with the first annual equinox, which takes place in March. The two equinoxes complement each other by flipping astronomical spring and autumn according to astronomical date and hemisphere. Accordingly, the Northern Hemisphere and the Southern Hemisphere experience the two seasons oppositely yet completely during the year.

graphic of high-resolution image of transition from spring equinox to autumn equinox in 2020 obtained by NOAA's GOES (Geostationary Operational Environmental Satellites)-East geostationary satellite, also known as GOES-16: via NOAA / NESDIS (National Environmental Satellite, Data, and Information Service) Center for Satellite Applications and Research (STAR)

The September equinox marks the overhead sun's crossing of Earth's equator. The September equinox announces the reach of the midpoint of the sun's annual zenithal (Middle English: cenyth; from Medieval Latin: cenit; from Arabic سَمْت, samt, “direction, path”) journey between the Northern Hemisphere's Tropic of Cancer, also known as the Northern Tropic, and its southerly equivalent, the Tropic of Capricorn, also known as the Southern Tropic.

The overhead sun's position over the Tropic of Cancer represents the sun's northernmost overhead point on Earth, as explained by Indian journalist and content writer Mahima Sharma in "September Equinox 2023: Date, Time and Significance," published Sep. 22, 2023, in The Times of India. The year's June solstice associates with this point.

The sun's apparent northward journey toward the Tropic of Cancer becomes a southward traversal after the instant of the June solstice. The sun's six-month southward travel is known as Dakshinayan (Sanskrit: दक्षिणायन, Dakṣinayana) in India, explains Mahima Sharma.

The overhead sun's equatorial crossing occasions the next destination. The overhead sun's arrival at its southernmost point, above the Tropic of Capricorn, occasions the December solstice, three months after September's equinox and six months after June's solstice.

The December solstice coordinates astronomical summer and astronomical winter with the June solstice. The Northern Hemisphere's astronomical summer and the Southern Hemisphere's astronomical winter connect with the June solstice. Contrastingly, the December solstice opens northern astronomical winter and southern astronomical summer.

Interestingly, the equator, which divides the Northern Hemisphere from the Southern Hemisphere, passes through 13 countries, according to Matt Rosenberg in "Countries That Lie on the Equator: Nations Along the Line That Divides the Earth in Two," updated Jan. 28, 2020, on ThoughtCo website. In South America, the equator divides three countries: Ecuador, Columbia and Brazil. The equator travels through the island nation of São Tomé and Príncipe of the west coast of Central Africa in the Atlantic Ocean's Gulf of Guinea. Also, Africa's six equator-straddling mainland republics comprise the Republic of the Congo, Gabon, Democratic Republic of the Congo, Uganda, Kenya and Somalia. In Maritime Southeast Asia, the equator journeys through four islands in Indonesia: Sumatra, Kalimantan, Sulawesi and North Maluku.

The equator distinguishes the northern and southern territories of two island nations by passing through their territorial waters, but not their landmasses. The atolls of Addu and Fuvahmulah lie near the equator in the South Indian Ocean while the other 24 atolls in South Asia's Republic of the Maldives occupy the North Indian Ocean. As the dweller of all four of Earth's hemispheres, Oceania's Republic of Kiribati claims locations north and south of the equator for its three distinct island groups of the Gilbert Islands, the Line Islands and the Phoenix Islands.

Technically, the astronomical seasons differ for the northern and southern components of these 13 equator-touching countries. Accordingly, while opening astronomical autumn for these countries' occupants in the Northern Hemisphere, the September equinox signifies astronomical spring for their regions in the Southern Hemisphere.

graphic of astronomical and meteorological seasons in 2022 in the Northern Hemisphere during Earth's orbit around the sun; image credit NOAA Office of Education/Kaleigh Ballantine: via NOAA Office of Education

Acknowledgment

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

Image credits:

graphic of astronomical and meteorological seasons in 2022 in the Southern Hemisphere during Earth's orbit around the sun; image credit NOAA Office of Education/Kaleigh Ballantine: via NOAA Office of Education @ https://www.noaa.gov/education/resource-collections/climate/changing-seasons

graphic of high-resolution image of transition from spring equinox to autumn equinox in 2020 obtained by NOAA's GOES (Geostationary Operational Environmental Satellites)-East geostationary satellite, also known as GOES-16: via NOAA / NESDIS (National Environmental Satellite, Data, and Information Service) Center for Satellite Applications and Research (STAR) @ https://www.nesdis.noaa.gov/news/noaas-goes-16-sees-the-autumnal-equinox

graphic of astronomical and meteorological seasons in 2022 in the Northern Hemisphere during Earth's orbit around the sun; image credit NOAA Office of Education/Kaleigh Ballantine: via NOAA Office of Education @ https://www.noaa.gov/education/resource-collections/climate/changing-seasons

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