Today will be the longest in terms of daylight hours for Australia this year, with the summer solstice occurring at 4:45pm EDST. The south pole is currently tilted towards the sun, meaning that our days are not only longer but the sun sits higher in the sky. The sun will pass directly overhead for locals in Rockhampton, which sits on the tropic of Capricorn. For those in southern cities such as Melbourne and Hobart, there will still be natural light past 9pm tonight. While days will gradually become shorter into January, there is a lag time for the Australian landmass and surrounding seas to warm up after the solstice. Therefore for most Australian capital cities (apart from Darwin where the wet season takes hold), average maximum temperatures continue to rise into January and hold steady into February before the cooler autumn months arrive. Traditionally in Australia summer is defined as the three warmest months based on the climate record. However, in some northern hemisphere countries, their definitions of seasons are based on the equinoxes and solstices. Therefore today marks the start of winter in countries such as the United States of America, who use this astronomical definition for their seasons.