*This chart shows the change in the length of daylight for a location in the Northern Hemisphere temperate zone. It has been estimated for approximately the latitude of New York City.

It should be noted that as one gets closer to the equator, the wave flattens out; as one gets closer to the North Pole, the wave gets more extreme.

For the Southern Hemisphere, move the wave 6 months along the time axis.

This causes the seasons.

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