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We're three million miles closer to the sun in January than we are in July. So why isn't it


There's something about the geometry of space that's never quite made sense to me. I know that the axial tilt of the Earth is the reason we have seasons, but if a slight angle away from the sun can make me see my breath in winter, why does being three million miles closer not make me melt in a pool of my own sweat? Is it really not any hotter when we're at our shortest distance from our star? And if it is, then why should the 23.5° tilt to our axis matter at all?

I have to re-Google these questions every year at the perihelion, the point at which we're the closest to the sun. Despite December 21 being the shortest day of the year in the northern hemisphere, it's not until early January that we reach perihelion, when Earth gets the most intense dose of solar rays it will receive all year. Averaged across the whole globe, we're getting sunlight 7-percent stronger in January than we are in July.

But it turns out that our distance to the sun actually has very little to do with the temperature we experience. It has far more to do with the angle at which the light hits us.

Light coming in at 90° hits as directly as possible. At the peak of winter in the northern hemisphere, the sun's rays are pointed right at the Tropic of Capricorn, which is 23.5° below the equator. That band is getting the most direct light. Everywhere else is getting hit at an angle, and that means that the same energy in each metaphorical ray is spread across a larger area, weakening the heating effects at any given point.

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