On average, Earth’s solar-heated global surface is warmer than the Moon’s by as much as 90 degrees Celsius! This is in spite of the fact that the mean solar flux – evened out globally and across the diurnal cycle – absorbed by the latter is almost 80% more intense than the one absorbed by the former.

**The Earth’s global surface**, absorbing on average **165 W/m ^{2}** from the Sun, has a mean temperature of

**~288K**(+15°C).

**The Moon’s global surface**, absorbing on average **295 W/m ^{2}** from the Sun, has a mean temperature of

**>200K**(-75°C).

A pure solar radiative equilibrium for each of the two bodies (according to the Stefan-Boltzmann equation: Q = σT^{4}, assuming emissivity (ε) = 1) would provide them with maximum steady-state mean global temps of 232K (-41°C) and 269K (-4°C) respectively.

As you can well gather from this, the Earth’s surface is 56 degrees *warmer* than its ideal solar radiative equilibrium temperature, while the lunar surface is at least 70 degrees *colder* than its ideal solar radiative equilibrium temperature. That’s a spread of no less than 126 degrees! On average …

Still, these two celestial bodies are at exactly the same distance from the Sun: 1AU.

So what could possibly account for this astounding difference between such close neighbours?

Very simple: **The Earth has an atmosphere. The Moon doesn’t.** Continue reading