By Sally Thorsteinsson and Michael Williams, UNE Discovery Voyager

Here in the Southern Hemisphere, the Winter Solstice has just past. From the 22 June, the shortest day and the longest night of the year are behind us. This is the time when the Earth’s south pole is pointed away from the sun due to the tilt of the Earth’s axis, so the sun is at its lowest point in the sky. In our temperate climate, I notice this most in three ways: the obvious one being darker mornings and earlier sunsets. The second one is the shadow cast by our house over our south-facing back garden – it is noticeably longer in the winter when the sun is lower in the sky than in the summer when the sun is high. From now on, the shadow will cover less of the garden as the sun’s angle increases.

And thirdly, how far the sun reaches into north-facing rooms in our house – you may also notice this in your home. In winter, the sun floods into our living room, casting long strips of brightness across the floor and warming the room even on the coldest sunny days. Opening the curtains in the morning, we can already feel the ‘glasshouse effect’ of the air being warmed between the glass and the fabric, and I imagine it streaming in and lifting the temperature of the room. Fortunately, in summer, when the South Pole is tilted towards the sun, the eaves of the house block some of that hotter sunlight; we really don’t appreciate its heating effects in the house then.

Post- Winter Solstice, the days will now lengthen, however, the sunrise will continue to get later for a couple more weeks. Because the earth has a slightly elliptical orbit around the sun, not perfectly circular, it means that in July, our winter, the earth is furthest from the sun. But the earth is spinning as well travelling around the sun, this gives us day and night. In the time it takes for earth to spin around once, the earth has continued to travel around the sun. Earth has to spin a bit more than once to be looking at the sun in ‘the same place’. The faster the sun moves, the longer this takes, the later the sunrise.

Because we are furthest from the sun in July, the earliest sunset and latest sunrise are slightly offset from the shortest day. The earliest sunset occurs slightly before the solstice (in Armidale June 10) and the latest sunrise happens to occur slightly after (July 2).

When the south pole is pointed away from the sun our hemisphere spends less time being warmed by it, hence the cooler weather in winter. In addition, the sun being lower in the sky means less direct (less intense) sunlight. It delivers less energy than summer sun.

You will also have observed that the winter temperatures are not at their coldest around the solstice, we still have that pleasure to come! This is due to a seasonal lag effect as the land and the sea take time to cool (and in summer, warm. This is often most noticeable at the coast, when the ocean can be at its warmest around Easter, when the air temperatures are already cooling).

Day length affects the patterns of the natural world; the timing of flowering, leaf drop, migration and breeding for instance. In humans it can affect our sleep patterns, physical activity and mood, and many cultural rites and celebrations recognise its significance to us.

While we can’t change the regional climate or the angle of the sun, we do have the opportunity to adapt our spaces to make the most of them. A classroom, house or other building intentionally designed to make the most of the sun’s energy is called a passive solar building. In temperate climates, this means warming a building in winter and protecting it from the overly heating sun in summer. It includes design features such as the overhang of eaves (relating back to the sun’s angle in the sky), orientation (the direction the building faces), and the location of windows. However, you don’t need to redesign your house to benefit from the sun. You can apply other simple things. For instance, in this area, planting a deciduous tree on the hot westerly side shades the wall in summer and allow sun though in winter. Modifying our environment to make it more comfortable begins with making observations about what is happening now and then thinking about which elements can be changed. How exciting – you can even apply your scientist skills – noticing things and asking questions about those things – to make your living environment more comfortable!

Daylight duration and time allocation of children and adolescents – ScienceDirect

It’s the winter solstice in Australia, so when will mornings get lighter? – ABC News

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