Why does it get dark quickly in winter?

23 September 2012


Why does it get dark quickly in winter?


Dave - This is mostly to do with the rate at which the Sun goes down over the horizon. If you think about the world being stationary and looking at the Sun going past you, it sort of goes up and then it comes down, and then it goes up... And you can imagine it being below the horizon as it goes around you. Now, in the summer then essentially, the whole thing is lifted up on the sky. So, it goes up really high and it comes down. It's starting to kind of flatten out as it goes below the horizon and then it comes back up again, and it's rising and falling relatively flat which means it's kind of just below the horizon for a very long time. It takes a long time to get a long way below the horizon, so it doesn't get dark very quickly. The same thing actually happens in the winter because you're looking at the flat bits of this wiggly sine wave near the top, so it's not going down below the horizon very quickly. At the equinoxes, around now, when it sets it's at the steepest part of the curve, so it gets below the horizon quickly. The same thing happens at the equator when it gets to the horizon very, very quickly and so, it gets dark much quicker at the equinox than it does in the midsummer and midwinter.

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