This week's equinox: the day light and dark strike a true balance
Tuesday, 18 March 2025
Paul Gorman is a senior journalist and award winning science writer. He will be writing about weather for Stuff.
If you’ve been feeling in a remarkable state of equilibrium in the past few days, considering the state of the world, it could be due to forces far more colossal than those prevailing on Earth.
New Zealand, like all the temperate countries in the Southern Hemisphere, is drifting a little closer to autumn every day. On Thursday this week we reach the autumn equinox at 10.01pm, one of two times in the year when the Sun is directly above the Equator and the Earth is not tilted towards or away from the Sun, producing almost the same amount of daylight across the world.
(Interestingly, as I write this, the sunlight is suddenly pouring through the window and full on to my computer screen, when just a few days ago it struck but a glancing blow.)
The days may still be warm – very warm in some cases earlier this week, with Australian outback air flooding across the Tasman – and the sun still strong and confident. But have you noticed the signs of imminent autumn? The glistening pearly dewdrops sprinkled across the lawns first thing after increasingly long nights? The need to pull the curtains a little earlier each evening?
The “official” arrival of autumn at your place depends which definition you wish to adopt.
The most generally accepted is that meteorological autumn lasts three months, from March 1 to May 31 – a convenient delineation given there are four seasons and 12 months in the year.
For convenient, maybe read too convenient. We all know the weather does not oblige the days of the calendar, particularly for the two transitioning seasons of spring and autumn.
While Kiwis enjoy complaining about the weather as much as any other nationality, we actually have it pretty good. Our spring can start early and eat into what might traditionally be winter months. It’s the same with autumn – it can start late and drift languorously on till winter’s inevitable arrival comes as a heck of a shock.
Of course, because autumn is a segue between summer and winter, the mellow days become fewer and further between as the months progress. March may have more warm northerlies than cold southerlies, but that has generally reversed by May.
Perhaps we should look at using astronomical autumn to define the season instead? This would make the first day of autumn March 20 or 21, depending on which day the equinox falls, arguably a more suitable date for New Zealand.
We could probably then run autumn through until the end of May, though by then the vivid leaf colours which usually peak around Anzac Day are long gone, and the gutters are full of mushy, slippery leaves.
For anyone else fascinated by the passage of the seasons, the rhythms of sunrises and sunsets and how they affect different parts of the country, the Time and Date website is a must.
On this week’s equinoctial Thursday, Auckland will have 12 hours and nine minutes of daylight, and the Sun will reach its highest elevation above the horizon of 54 degrees at 1.28pm.
Wellington gets the same daylight hours (plus 41 seconds), with the Sun at its zenith of 49 degrees at 1.28pm, while Christchurch has 12 hours, 10 minutes and four seconds, and the Sun is at its 47-degree zenith at 1.36pm.
In the deep south, Invercargill has daylight of 12 hours, 10 minutes and 37 seconds, with the Sun at its maximum elevation of 44 degrees at 1.54pm.
Hate to say it, but from here it is all downhill in terms of day length. Also, the angle of New Zealand’s landmass means places further west and south will start to have much later sunrises for the winter, even if sunsets are much the same throughout the country.
By the winter solstice, on June 21, Auckland’s daylight will last nine hours, 37 minutes and 53 seconds, Wellington’s nine hours, 11 minutes and 22 seconds, Christchurch’s eight hours, 56 minutes and 21 seconds, and Invercargill’s eight hours, 34 minutes and 59 seconds.
The Sun’s peak above the horizon will range from 30 degrees elevation in the north to just 20 degrees in the far south.
What is notable about the weeks around the equinox is how fast daylight is being lost each day, by about three minutes. Daylight Saving Time (DST) comes to an end early on April 6 – that means for the next two weeks there is quickly decreasing evening light and, arguably, quickly increasing pointlessness to being an hour ahead of New Zealand Standard Time (NZST), especially as it is also much darker later in the morning.
The government last changed the dates of daylight saving in 2007, extending it to a period from the last Sunday in September to the first Sunday in April. That means we now have more DST – 27 weeks a year – than NZST.
What do you think? Is that too much, or not enough?