The days are getting shorter and colder and the afternoons spent sunbathing are long gone, especially in the southern states.
But if you think the mornings are dark and gloomy now, wait until we reach the winter solstice.
Next Tuesday, June 21, the southern hemisphere will experience the shortest day and the longest night of the year.
And while we are immersed in darkness, the northern hemisphere will enjoy the summer solstice, the longest day and the shortest night of the year.
So what’s behind this astronomical phenomenon?
Why do we have the winter solstice?
It all comes down to the fact that the Earth is a little uncomfortable on its axis.
Instead of rotating perfectly vertically, our planet is tilted about 23 degrees.
This inclination is what gives us the four seasons: winter, spring, summer and autumn.
Also, the Earth does not travel around the Sun in a perfect circle, but in a football-shaped ellipse.
As the Earth completes its orbit around the Sun each year, different parts of the planet tilt toward our star at different times and receive more direct sunlight.
The axial tilt of the Earth and its elliptical orbit give rise to the seasons, solstices and equinoxes. (Getty Images: Stocktrek Images / Photon Illustration)
This causes warm weather and short nights. Welcome to summer!
At the same time, the other side of the world is moving away from the Sun, causing cold temperatures and longer nights. This is winter.
“During the winter, our part of the Earth is tilted away from the Sun and therefore [the Sun] it’s not above the horizon for so long every day, ”said Tim Bedding, an astronomer at the University of Sydney.
When is the Winter Solstice?
The winter solstice marks the point at which the southern or northern hemisphere tilts farther from the Sun.
In the southern hemisphere, this falls between June 20 and 22, while in the northern hemisphere it usually happens on December 21 or 22.
The spring and autumn equinoxes occur when the Sun appears directly above the equator, making the days and nights roughly the same.
Why doesn’t it happen on the same day every year?
While our reliable calendars help us chart the year, they are not perfectly in sync with the Sun’s movements.
It takes the Earth about 365 and a quarter days to revolve around the Sun, so we have years of transition, said Professor Bedding.
“A year is not exactly an even number of days,” he said.
And what about late sunrises and early sunsets?
Similarly, the duration of a solar day is not exactly 24 hours.
This means that the solar noon, the time when the Sun reaches the highest point in the sky, does not occur at the time when your clock strikes noon.
Around the winter solstice, solar noon occurs a few minutes later than the day before.
Sunrises and sunsets also return later after the winter solstice.
This means that the earliest sunset will occur before the winter solstice, while the last sunrise will occur after it has passed.
“What matters is not the setting and sunrise, but the difference between them is shorter [on the winter solstice]”said Professor Bedding.
Is the shortest day of the year also the coldest?
Usually not. This is due to a strange delay called seasonal delay.
“There’s a delay because the Earth takes a while to cool down and reheat,” Professor Bedding said.
In Australia, the main culprit is the ocean, which takes longer to cool and warm than the earth due to its higher heat capacity.
The ocean takes longer to warm up and cool than the earth, which contributes to seasonal lag. (Getty Images: James D Morgan)
Consider heating a pot of water (or winter warming soup) on your stove.
Instead of going from cold to boiling as soon as you turn on the heat, the liquid will take a few minutes to warm up.
Similarly, the pot will gradually cool once the fire is extinguished.
It’s the same idea with Earth. Although we will gradually receive more sunlight after the winter solstice, the average temperatures will take a few months to catch up.
How short will the day be?
It depends on where you are.
At Darwin, you will experience just under 11.5 hours of daylight at the winter solstice, while Hobart will have about 9 hours of sunshine.
city
Sunrise of the solstice
Solstice sunset
Duration of the day of the solstice
Sydney
6:59 p.m.
16:53
9 hours and 53 minutes
Melbourne
7:35 h
17:08
9 hours, 32 minutes
Brisbane
6:37 h
17:01
10 hours, 24 minutes
Hobart
7:41 h
16:42
9 hours, 0 minutes
Adelaide
7:23 h
5:11 p.m.
9 hours, 48 minutes
Perth
7:16 p.m.
5:20 p.m.
10 hours, 3 minutes
Darwin
7:06 p.m.
6:30 p.m.
11 hours, 23 minutes
“The farther you are from the equator, the more difference there is,” Professor Bedding said.
“If you’re in North Queensland, you probably won’t even notice a difference, but if you live in Tasmania, you’ll definitely notice a big difference.”
But if you really want to feel the darkness of winter, look no further than the South Pole, said Professor Bedding.
From March, the South Pole is witnessing its last sunset for a few months, as it passes into a period known as polar night.
“The sun does not even exceed the horizon: it is night for 24 hours.”
Polar night gradually recedes after the winter solstice, but the South Pole still doesn’t see a decent sunrise until September.
What can I see in the night sky?
If the idea of spending most of the day in the dark is disappointing, you may want to look at the sky early in the morning if you can cope with the cold.
“There are beautiful planets visible in the morning sky,” said Professor Bedding.
If you look east, you will see Venus, Mars, Jupiter, and possibly even bright Mercury appearing in a straight line in the sky just before dawn.
“As far as astronomers are concerned, the winter solstice is a good time because we have more night and astronomers love the night,” he said.
“So if you like looking at the stars, this is a perfect time of year.”
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