The winter solstice is here - but what does it mean?

As northern hemisphere prepares for the arrival of the longest day of the year with the summer solstice, the rest of the world is bracing for winter solstice.

For Australians, the winter solstice - otherwise known as the shortest day of the year - will be upon us Friday night.

But what actually is it?

The winter solstice marks the shortest day of the year. It’s the day that has the least daylight hours of any other in the year.

This happens when the South Pole is tilted furthest away from the sun. The further south you are, the shorter the day will be.

It is also the unofficial start of winter for us southern hemisphere dwellers.

Google has even marked the occasion on June 21 with a Google Doodle of the Earth topped with a snowman.

“Because the path of the Earth around the sun is an ellipse, not a circle, and because the Earth is off-centre on its axis, these combined phenomena can create up to several minutes difference between solar and mean time,” according to Geoscience Australia.

What about the summer solstice?

In contrast, summer solstice is the northern hemisphere tilted most closely towards the sun.

For us, the summer solstice occurs once a year in December when the sun's track across the Australian sky reaches its highest point.

It is the day that has the most daylight hours of any in the year. The summer solstice usually occurs on 22 December, but can occur between 21 and 23 December.

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