I always thought the shorter day means the earth is further away from the sun, so why is all of winter after that point? (Similarly with summer).
In: Physics
1. Winter is not caused by the distance to the Sun, in fact we’re closest to the sun in early January. Seasons are caused by axial tilt.
2. There’s a delay in the system. Even though we get more sunlight every day after the solstice, it takes a while to turn the downward trend and provide enough sunlight to heat up.
Firstly, the seasons and lengths of the days have nothing to do with our distance from the Sun. The seasons are caused by the fact that Earth is tilted on its axis. In Winter one hemisphere is tilted away and so the sun is lower in the sky and its light is spread out over a larger area. Remember that while it’s winter in one hemisphere it’s summer in the other.
Secondly, seasons are defined in numerous different ways. The astronomical reckoning uses the solstice and following equinox to define it, because it takes a while for the planet to cool down and so the coldest period usually falls roughly between those points. Other methods just use, say, December-February etc.
It’s rooted in astronomical tradition. Back in the days, many people used to celebrate the winter solstice (shortest day), summer solstice (longest day), as well as the equinoxes in the middle between those two. So if you want to find an exact date where winter begins, the winter solstice is a pretty good one.
Of course, this doesn’t perfectly align with weather patterns in most of the world. So for meteorogists, winter goes from december to the end of february, which are the coldest months in the northern hemisphere.
That said, there are also much different definitions for seasons, for example some tropical areas only know dry season and wet season.
The summer solstice, for example, represents the day that sunlight is hitting you most directly. All else being equal, that is the day when your local environment heats up the fastest. It will, however, continue to heat up after that day, so the hottest days are after it.
As an analogy, when I cook spaghetti, I will turn the stove on high until the water starts to boil, then I turn it down. The hottest time occurs after the highest stove setting.
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