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.
I guess the person who 'proved' the world was round was Ferdinand Magellan, who was the first man to sail around the world. That was the first time it was conclusively proven that the world was round. Note that he never disproved that a belief in flat Earth was wrong. Neither Magellan nor anybody he ever met believed the Earth was flat. All Europeans knew it was round. Other cultures may have thought it was a dome but nobody had ever thought it was flat. ____Those who have answered âColumbusâ are completely wrong.