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Winter starts now, right? Depends where you stand on solstice and the seasons

Kate Doyle, Sunday June 21, 2020 - 07:40 EST
ABC image
The winter solstice is the shortest day and longest night in our passage around the Sun. - ABC

Every year as the temperatures get cooler and the days get shorter we all know winter is coming. But what exactly do you call "winter"?



Here in Australia we generally use the beginning of June to mark the start of the coldest season but the solstice means something different to Indigenous Australians and people in other parts of the world. So which is best?

As Dr Blair Trewin, senior climatologist at the Bureau of Meteorology and general fount of wisdom for all things historical and weather, explains seasons everywhere "are a matter of how popular usage has evolved — there isn't really anything 'official' about them".

But arguing over largely arbitrary definitions is a favourite pastime in the world of weather, so let's indulge and compare astronomical, meteorological and Indigenous perspectives.

Astronomical seasons

It's a common misconception that the seasons are determined by a change in distance between us and the Sun. It is actually the tilt of the Earth that has the biggest effect on the distribution of energy around the globe.



Model globes are not displayed on a jaunty angle simply for aesthetic effect. Their tilt is representative of the angle of the Earth relative to our orbital plane around the Sun.

Most importantly, though, for our seasons, weather, oceans, crops, flora, fauna, climate and life as we know it generally, the part of the world pointing toward the Sun changes as we orbit around it each year.

"The solstices describe the points in the Earth's orbit where the tilt is pointing towards or away from the Sun," Dr Vanessa Moss, astronomer at the CSIRO, Australia's national science agency, said.

Our winter solstice occurs when the southern hemisphere is pointed most away from the Sun, which coincides with when the northern hemisphere is most pointed towards the Sun, making it the northern hemisphere's summer solstice.



The tilt of the Earth dictates both how long the Sun is "up", as well as how much the Sun's energy spreads over the globe.

As the southern hemisphere is tilted further from the Sun, the angle at which sunlight hits the Earth is shallower, meaning the light and energy spreads across a larger area.

"So because the energy is spread out, it also means that the Sun feels weaker. It's not as intense and the heat is not as effective," Dr Moss said.

This is why it is colder in winter.

Beware the lag

The winter solstice may be the shortest day in terms of daylight and when there is least energy in the southern hemisphere, but the land, atmosphere and, especially, oceans are still cooling.

"It means there is a lag associated with how long it takes us to feel on Earth the effects of this peak energy or minimum energy," Dr Moss said, which is why it makes sense not to use the solstice to mark the start of winter, or even middle of winter.



The solstice marks the middle of the time of low energy input and even then the coldest time of year is generally after the winter solstice.

Of course, when exactly local weather conditions conspire to bring the coldest days for each location depends on more than just raw energy from the Sun.

Which brings us to . . .

Meteorological seasons

Meteorological seasons are largely defined by Gregorian calendar months.

"Popular usage in Australia (outside the tropics) tends to follow the meteorological seasons quite strongly," Dr Trewin said.

Most Australians define winter as starting on June 1 and lasting until the end of August. Each of the seasons last three calendar months, breaking up the year into four equal parts.

Dr Trewin said why, exactly, we took on meteorological seasons when other parts of the world, like the US, had stuck with astronomical seasons was unclear.



"However, it's worth noting that the coldest 90 days of the year start within a few days of June 1 almost everywhere in Australia, except in southwest WA where it's a week or two later," he said.

So it make sense that winter centres on the coldest part of the year, plus the convenience of the season starting on the same day at the beginning of the month does make the paperwork easier.

But as with anything arbitrary and dependent on place, there are many ways to define the seasons and the tropics' wet and dry seasons are just the start.

Indigenous seasons

Across the country, indigenous communities have a very different view of the seasons.

Tremaine Patterson, Banbai ranger at Wattle Ridge Indigenous Protected Area, near Guyra in the New England region of New South Wales, said his people had a far more fluid approach to the seasons.

"Like much of the culture in some areas, knowledge was lost due to people not being able to speak language because it was forbidden," he said.

"But to my knowledge, we didn't go off summer, winter, autumn, spring. We had our own bio-cultural indicators that we went off, that were taught and passed down through generations."

Some of these indicators included flowering plants and animal behaviours.



"We told stories with the stars and the moon and also off the land, the country. Different waters, different types of air, when it is colder, hotter.

"We had all these indicators that our people read from. Just for instance, in June it was cold but dry and frosty. So it would be an excellent time for cultural burning, which would regenerate country."

The Banbai Nation is one of the many regions working to record this cultural knowledge, specific to each region, in

"I've been on Banbai for 11 years now and I didn't really know much about culture [before then]," Mr Patterson said.

"When I found out we didn't have a spring, summer, autumn and all that, we had our own indicators, it has driven me more to find out more about what we did as people.

"Some of our old fellas are passing on now and knowledge is just going with them. It's pretty saddening.

"To be able to read country is more in depth, I think. It's an amazing thing to be a part of and to learn."


- ABC

© ABC 2020

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