What percentage of the Earth's surface lies between the Tropic of Cancer and the Tropic of Capricorn?

Answer 1

The tropics are defined as the area between the Tropic of Cancer and Tropic of Capricorn, each of which lies 23.5° of latitude away from the equator. This is the part of the Earth where the sun is capable of passing directly overhead at least once per year; it is also on average the warmest region of the planet.

Common sense says that since this covers a span of 47 degrees, and there are 180 total degrees of latitude, this area must be around 1/4 (47/180, or 26%) of the total surface of the Earth.

This is a vast underestimate, which has to do with how the surface of a sphere is actually calculated. Without going into the math -- if you're interested, please see the attached link -- it turns out that because this band encompasses the widest part of the globe, it actually turns out to be just under 2/5, or a whopping 40%, of the surface area of the entire planet!

If you take the sine of 23.5 and multiply it by 100, you get 39.9.

Note that this total includes land and water areas together; I'll leave it to some other enterprising scholar to calculate the percentage of the land area which currently lies in the tropical region. However, by coincidence, 40% of the world's population currently lives in the tropics; although this number is forecast to rise substantially by the end of the century.