Are there more DAY or NIGHT hours in a whole year?We all know that days are longer during Summer, and shorter in Winter. In fact, they are equal all year round in the equator. So the answer should clearly be: there is as much night as there is day!
Which is well thought, but wrong. There are two good reasons for this, but before we get to them we need to look at a pencil in a water glass.
When light crosses different materials it changes its path. This is why a straw in a glass of water looks broken, as you can see in the image below. For this same reason we misjudge the depth of submerged objects from above water, thinking they are closer than they really are. When the light comes out of the water it makes an angle, and our perception is fooled.
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The same happens when light crosses a material with changes in its temperature or density, and the atmosphere is no exception. In fact, this is the explanation for mirages.
Mirages happen because the light is bent when it passes through different temperature layers in the atmosphere. This can make us see the sky apparently coming from the ground, like reflected by water, or inversely (with cold air) objects floating in the sky, like ghost ships.
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The light coming from the Sun and the stars is also bent when it reaches the atmosphere. The result is that when we see the Sun meet the horizon it should have actually disappeared some minutes before. And when we see the Sun at dawn, it really should take a few more minutes to come up in the sky. So, day after day, we are getting a few extra sun-minutes.
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But if we lived in the Moon, where there is no atmosphere and no light-bending nonsense, then surely night and day would be equally long in a lunar year, right?
Still no. The reason is that the Sun is not a dot of light like the rest of stars, but it is big in the sky. This means it takes some time to set and rise. And even if we count twilight hours as night, we have to talk about daytime at least while some part of the Sun is over the horizon. Which is even more extra day-minutes everyday.
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