While today is actually the shortest day of the year, with fewer than 10 hours' daylight to enjoy, the Australian National University engineering department staff and PhD students took part in their annual winter solstice dip yesterday morning on their way to work.

They are usually engaged in research to do with sunlight but there will be a shortage of it today with the sun due to rise at 7.12am and set at 4.58pm. The winter solstice, when the sun will be at its furthest point north for the year, is due to take place at 9.59am.

The days will get longer from here on, but as Sydney Observatory's curator of astronomy Dr Nick Lomb notes, the initial difference will only be a matter of seconds.

The winter solstice swim in Canberra, meanwhile, has been organised for at least the past eight years by the ANU's Mike Dennis.

The former New Zealander has marked the shortest day by leaping into cold water wherever he is in the world, whether it was the beaches of Taranaki or the North Sea in Europe.

''I don't know why we do it we haven't worked out a good reason,'' Dr Dennis said.

''It's not too bad in there.''

One of his mates was not so sure: ''Oh Mike, it's bloody cold. It hurt''.

Before yesterday's swim, there was an official reading of the lake water, which came in at a brisk 11 degrees.

Some of the dippers were well-prepared like ANU physicist Gert Wantenaar, who brought a large container of previously boiled water to pour over himself after the swim. He was literally steaming.

Maria Colom and Marta Vivar are studying in Canberra from their usual home in Spain.

''We're the crazy Spanish people,'' Ms Vivar said, after a dive into the lake. ''We usually celebrate the summer solstice, when it's warm.''

Not so crazy.

Others who bravely took part were: David Jacquier, James Cotsell, Ben Buchler, Evan Franklin, Joe Coventry, Chris Samundsett, Andrew Thomson, Jessica Preston, Rachel Poldy, David Barton, Rebecca Dunn and Vernie Everett.

And there was some concession to the usual winter solstice delights that might otherwise involve feasts and and wine and open fires. After the swim, everyone headed to the Yarralumla Bakery for hot chocolate.

The shortest day came as Canberra enjoyed with some winter rain overnight on Thursday and yesterday. Tuggeranong had received 6.2mm and Canberra airport 5mm to yesterday afternoon. Today is forecast to be mainly fine.