In 240 BC, the Greek astronomer, geographer, mathematician, music theorist and librarian Eratosthenes of Cyrene (c. 276 BC – c. 195/194 BC) calculated the circumference of the Earth without even leaving Egypt. Here’s how: Eratosthenes knew that at local noon on the summer solstice (at the time of the longest day, about 21 June in […]
Earth, the blue planet: the oceans combined with the atmosphere makes the planet look blue. So its color mainly comes from water. About 71% of the Earth’s surface is covered with water, in fact, Earth is still the only planet we know where water can exist in liquid form on the surface. Water is also […]
The “Seven Wonders of the World”, also known as the “Seven Wonders of the Ancient World”, describes seven great constructions known in the Hellenistic period Notes 1. None of them but the Great Pyramid of Giza (Kheops Pyramid) do not exist today.