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In 1861, the unsurpassable Charles Dickens penned the words: "It was one of those March days when the sun shines hot and the wind blows cold: when it is summer in the light, and winter in the shade." There are few sentences that capture the essence of how important it is that Earth is at the Goldilocks distance from the Sun. Not too hot, not too cold, but just right.
The distance from Venus to the Sun is 72.3% as far as the distance from Earth to the Sun, and so it gets 191% or nearly twice the sunlight of Earth. That's 243,000 lumens per square meter at Venus' orbit. This increased solar irradiance combined with a healthy amount of carbon dioxide and sulfur dioxide in Venus' atmosphere that trap in heat, yield an average temperature of 864 F at the surface. That's even a little bit hotter than papa bear's porridge.
Conversely, the distance from Mars to the Sun is 152% of the distance of the Earth to the Sun, and so Mars only gets 43% of the sunlight that the Earth gets. That's 55,000 lumens per square meter. The lower solar energy that Mars receives combined with its thin atmosphere yield an average temperature of -81 F at its surface. And yep, mama bear's porridge is frozen solid at this temperature.
With earth's average surface temperature of 59 F life on the planet is pretty good. Nine degrees (5 C) colder and we are in an ice age. Nine degrees (5 C) hotter and we have oceans rising and agricultural areas tuning into desert. That's what I mean by baby bear's porridge being 'just right?'
So how far is the sun from earth? I'm going to give you the exact answer, and I'll show you why it is the exact answer, but there is a lot more to it than just a single number. The exact answer is 92,955,807.2730255 miles.
Astonomical Unit
Is Earth Getting Closer to the Sun?
