Are caused by the Earth’s tilt. As the Earth goes around the sun, the tilt of Earth’s axis — 23.5 degrees — causes at different times of the year, the two hemispheres, North and South, to be either tilted towards the sun or away from it.

In Winter, and closer to the Poles, because light from the sun hits at a greater angle, the solar energy gets spread over a larger area. This makes it weaker, cooler and gives rise to Winter.

In Summer, and closer to the equator, light from the sun hits more directly and so is concentrated on a smaller area making it stronger.

The tilt also means that the number of daylight hours is greater in the Summer than in the Winter, and hence the amount of time it gets heated, which also contributes to the seasons.

Seasons are reversed in the two hemispheres, so if it’s Winter in the Northern Hemisphere it’s Summer in the Southern and vice-versa. The further from the equator you go, the bigger the effect of the seasons. So, temperatures in Ecuador stay relatively constant throughout the year, while the poles experience extremes of 24-hour daylight or 24-hour night and great freezes and great thaws.

PSThis is a correction to my original Seasons sketchplanation which implied that temperature difference was more due to the increased distance from the sun due to the tilt. This is not correct, and it’s taken me, embarrassingly, a long time to right it. Thanks to Adrián Fernández Martínez, marjancek and Reasons2AvoidAndroid for putting me straight. 

Seasons

The range around a star that’s not too hot and not too cold to support life. If you were looking for planets that may support life as we know it in distant solar systems it seems a good idea to look for planets in the Goldilocks Zone.

The Goldilocks Zone

…regulate temperature and (maybe) to keep feathers clean while eating. Keeping the feathers clean was my inspiration for this sketchplanation - there’s something about the cold practicality of not messing up your feathers while you’re tucking into some carrion. However, it looks like it is more likely to be for the more prosaic reason of regulating temperature and keeping cool. As Dominic McCafferty, at the University of Glasgow points out:

‘…other groups of scavengers, particularly giant petrels, have feathered heads. Large mammalian scavengers also don’t have bald heads, so why vultures?’

Should you be interested, read more at the University of Glasgow’s Why do vultures have bald heads?

Sketchplanations tagged with temperature