The summer solstice marks the longest day of the year. (ABC News: Andrew O'Connor)
Australia will experience its "longest day of the year" tomorrow as the Southern Hemisphere experiences its summer solstice.
But just how much daylight you'll get depends on where you are in the country.
Here's what you can expect.
What is the summer solstice?
It's often called the longest day of the year.
But technically, it's the day with the longest stretch of daylight over a 24-hour period.
It's when our side of the globe — the Southern Hemisphere — is at its closest tilt toward the Sun.
The Earth's tilt determines the solstice for the respective hemispheres. (Bureau of Meteorology)
At the same time, the Northern Hemisphere will be experiencing its winter solstice — when the North Pole is at its furthest tilt away from the Sun.
These phenomena, as well as the changing of seasons, all occur because of the Earth's 23-degree tilt, which exposes different parts of the planet to more sunlight as it orbits the Sun.
When is the summer solstice in Australia?
The summer solstice falls between December 21 and 23 in the Southern Hemisphere each year.
This year, it will fall on Saturday, December 21.
While we usually think of solstice as referring to a whole day, there's actually a specific moment when the Southern Hemisphere will be at its closest tilt toward the Sun.
Here's when the exact moment will fall for your time zone:
- AWST: 5.19pm
- ACST: 6.49pm
- AEST: 7:19pm
- ACDT: 7:49pm
- AEDT: 8:19pm
The Southern Hemisphere will be at its closest tilt toward the sun on Saturday. (AAP: Bianca De Marchi)
How long is the 'longest day of the year'?
That depends on where you are in Australia, because places further from the equator get more daylight during summer than those further north.
Here's how many hours of daylight our capital cities will get:
- Adelaide: 14 hours and 31 minutes
- Brisbane: 13 hours and 52 minutes
- Canberra: 14 hours and 33 minutes
- Darwin: 12 hours and 51 minutes
- Hobart: 15 hours and 21 minutes
- Melbourne: 14 hours and 47 minutes
- Perth: 14 hours and 14 minutes
- Sydney: 14 hours and 24 minutes
Why are the days longer in summer?
Because of the Earth's tilt toward the Sun.
It means when the Southern Hemisphere is facing the Sun more directly, the Northern Hemisphere is tilted away.
Australia experiences winter during the middle of the year, when the Southern Hemisphere is tilted away from the Sun. (ABC: Julie Ramsden)
This is why, when we experience summer here in Australia, the Northern Hemisphere experiences its winter.
During this time, we get more daylight hours and the light is spread over less surface area, meaning the days get warmer.
As for the days being longer in summer and shorter in winter, here's how science presenter Bernie Hobbs explained it:
"In summer, days are longer because more hours are spent facing the Sun.
"And they're hotter because we're facing the Sun more head-on — so we get hit by more rays of sunlight than if we were on an angle."
When do the days start getting shorter?
After the summer solstice.
Each day will get a fraction less daylight than the previous day's until we reach the winter solstice on June 21 next year.