Cloud tops reaching to a level where the temperature is at least: minus 18Â°C. (but see 4, below) A large amount of energy available to be released (CAPE). If the CAPE is large, then the cloud top temperature can be as warm as minus 15Â°C, and thunder will occur - however, these are the exception rather than the rule.
Eratosthenes calculated the circumference of the Earth without leaving Egypt. Eratosthenes knew that at local noon on the summer solstice in the Ancient Egyptian city of Swenet (known in ancient Greek as Syene, and now as Aswan) on the Tropic of Cancer, the Sun would appear at the zenith, directly overhead.
Because the Earth slightly flattens out at the poles, its shape is an oblate spheroid, meaning that it is similar to a sphere but is not perfectly regular. The circumference of the Earth at the equator is 24,902 miles. Again, that is a bit more than its circumference from pole to pole, which is 24,860 miles. At 5.52 grams per cubic centimeter, the Earth is the densest planet in the solar system.