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.
But they donât. This is because the earth is round, and not flat: Eratosthenes (276-194 BCE) used this principle to calculate the circumference of the Earth quite accurately. To see this demonstrated, refer to my experiment video about Eratosthenes and the circumference of the earth â âThe Earthâs curvature is tasty!â.