The winter solstice in Australia is today. Here's how the shorter days of winter can affect your sleep patterns

Australia will have its "shortest day of the year" today as the southern hemisphere experiences the winter solstice.

Where you are in Australia will determine just how much daylight you will get.

The shortest day of the year can also impact your sleep.

Here's what that means.

When is the winter solstice?

Saturday, June 21.

According to timeanddate.com, the exact moment the southern hemisphere is at its furthest tilt from the Sun will be at 12:42pm AEST.

What is the winter solstice?

While the winter solstice is referred to as the shortest day and longest night of the year, it actually just means it is the day with the least amount of daylight hours.

That's because it's when the southern hemisphere is at its furthest tilt away from the Sun, meaning we get less sunlight.

At the same time, the northern hemisphere will be experiencing the summer solstice, which is the longest day of the year.

This happens because the Earth tilts at about 23 degrees, meaning that when one side is closest to the Sun, the other side is furthest away.

As the Earth does a lap around the Sun each year, different parts of the planet get more sunlight than others.

When do the days start getting longer?

After Saturday, each day's total sunlight hours will get a fraction longer than the previous day until we reach the summer solstice on December 22.

What does the winter solstice symbolise?

According to the astronomical definition of the seasons, the winter solstice in some places marks the beginning of winter.

But in Australia, where only meteorological seasons are observed, this is not the case.

That's why the beginning of winter is June 1 here.

In some cultures, the winter solstice is celebrated as a time of rebirth because the days get longer.

Do long nights throw off my sleep schedule?

Because it is getting dark so early and the days are shorter, some people may experience changes in their sleep schedule and quality.

Elise McGlashan, from the University of Melbourne's John Trinder Sleep Laboratory, says shorter days and longer nights mean less sunlight, which can change circadian rhythms.

The circadian rhythm is the internal body clock that regulates sleep.

"Those changes in sleep can also be accompanied by changes in timings and function of our internal clock and the function of our clock is mainly driven by environmental light exposure," she says.

"In summer, we know the sun might be up until it's close to someone's bedtime, and part of the reason people are sleeping a little longer is they aren't getting those light cues when they're trying to wind down.

"But during winter, there is less light and more time to wind down."

When there is less light exposure, the body produces more melatonin — a hormone that makes people feel sleepy — and less serotonin, which can lower mood and energy, leading to feeling tired or sluggish.

As the sun comes up later, it may be tempting to sleep longer but oversleeping can also impact health.

Dr McGlashan recommends getting outside for some sunlight during the day and letting sunlight into your bedroom in the mornings if possible.

"Our rhythms need bright days and dark nights," she says.

"It can be hard to motivate ourselves to go outside in winter, particularly in a really chilly location, but even on those overcast days, the light outside is going to be brighter than indoor lighting.

"It's still really helpful for your body clock and sleep to get outdoor lighting every day."