September 1 or 23?
September is the first month of spring, so most accept it begins on the first day of that month.
But as Stardome Observatory astronomer Josh Aoraki said, “there is no real ‘correct’ answer, as a season is really just a human-made construct of time”.
“There is no real ‘correct’ answer” to when spring begins, Stardome Observatory’s Josh Aoraki says. Photo / Michael Craig
“In saying that, there are three main factors that I’d take into consideration – meteorological, astronomical, and ecological/social.”
MetService meteorologist Mmathapelo Makgabutlane said the astronomical definition tracks seasons according to the earth’s position around the sun, a practice used for thousands of years.
Astronomical spring begins on the spring equinox – when the sun passes directly over the earth’s equator – which falls between September 22 and 23 in the Southern Hemisphere.
“This means spring goes until the summer solstice around 21 or 22 December,” Makgabutlane said, noting that our winter is also four days longer than the Northern Hemisphere’s.
“The earth’s orbit is slightly oval-shaped [rather than a perfect circle] and the earth speeds up a bit during our summer.”
Astronomers therefore mark seasonal changes by correlating the position of Earth around the sun with four divisions in the calendar year.
These divisions – the solstices and equinoxes- work as seasonal tentpoles.
“By this definition, spring for us will begin on the equinox which starts on September 23 and ends on the solstice which is on December 21,” Aoraki said.
Meteorological spring runs from September 1 to November 30, while astronomical spring begins on September 23. Photo / 123rf
What do meteorologists think?
Meteorologists and climatologists use the meteorological definition of the seasons – the ones we’re most familiar with – which are directly tied to the calendar months.
“By this definition, spring runs from September 1 to November 30, with meteorological summer starting on December 1 to the end of February,” Makgabutlane said.
“Using the calendar months has a practical use for things like long-term tracking of climate records since the seasons always fall on the same days.”
By following the meteorological definition, the Southern Hemisphere has a 92-day winter and 90-day summer, with an extra summer day during a leap year.
What about the environment’s role?
Nature also plays a part in determining when seasons start and end, and many cultures use environmental cues or tohu (signs) like the flowering of a plant or migrating birds to mark the occasion.
“Plants and animals are able to sense when the right time is to do what they need to do, and sometimes that’s earlier, other times that’s later,” Aoraki said.
Ecological signs, like the welcoming of lambs, also indicate spring’s arrival. Photo / Sylvie Whinray
“Here in Aotearoa, the call of the pīpīwharauroa/shining cuckoo is often used as a sign of spring when the birds return to New Zealand as it begins to get warmer,” Makgabutlane added.
Meanwhile, New Zealand’s seasonal temperature changes often lag by a few weeks, so the changing of seasons can almost feel muted to begin.
“Our temperatures are closely tied to the ocean, which warms and cools more slowly than land, so it takes a little longer for temperatures to catch up.”
Does it matter which one I use?
“Although the two definitions have the seasons start and end on different days, broadly speaking, they both cover the warmest, coldest, and transition times of the year,” Makgabutlane said.
“Which one people use is down to whichever is most relevant for them. As a meteorological agency, MetService uses meteorological spring for practical and climate record keeping purposes.”
While each definition serves its own purpose, Aoraki said they exist as “arbitrary ways for humans to understand the division of time and help us organise our lives around them”.
“The earth’s tilt, equinoxes and solstices, and seasons will change over aeons, as will the meteorological markers of a season, so neither would be relevant in thousands of years.”
Tom Rose is an Auckland-based journalist who covers breaking news, specialising in lifestyle, entertainment and travel. He joined the Herald in 2023.
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