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 leaving Egypt. Here’s how:
Continue reading How Eratosthenes calculated the Earth’s circumference
A beautiful video, once again, from Michael Stevens, titled “How Earth Moves”. Michael explains many concepts, including “sub-solar point”, “sidereal day vs solar day”, or “how Earth moves in the space” etc, and he is doing it in a very simplified manner. Enjoy!
Continue reading How Earth Moves (Video)
In 1950, the Italian physicist Enrico Fermi was chatting with his colleagues at the Los Alamos National Laboratory(1). They talked about recent rise in UFO reports, then the conversation shifted to other subjects. But during the lunch, Fermi suddenly asked “Where is everybody?”. He was talking about the extraterrestrial life, especially intelligent life. He made some calculations on the probability of Earth like planets, the beginning of life, the probability of intelligent life and high technology and concluded that we ought to have been visited long ago and many times over.
But, there is no reliable evidence aliens have visited Earth and we have observed no intelligent extraterrestrial life with current technology nor has SETI found any transmissions from other civilizations. The Universe, apart from the Earth, seems “dead”.
So, where is everybody?
Continue reading Are we the first?
A nice interactive webpage by the BBC – The British Broadcasting Corporation: how you and the world have changed since you were born? You’re simply entering your birth date, gender and height; selecting units (metric or imperial/US) and then watching how our planet (and you) has changed in your lifetime.
Continue reading Your Life On Earth (presented by BBC)
No, no no, and again: no! The Earth would NOT look like this without water. Please stop sharing this nonsense.
Continue reading No! The Earth Would NOT Look Like This Without Water
It’s one of the basic Newton laws: how fast something falls due to gravity is determined by a number known as the “acceleration of gravity”, which is 9.81 m/s2 at the surface of Earth. The acceleration of gravity, shortly “a” means that in one second, any object’s downward velocity will increase by 9.81 m/s because of gravity. The gravity accelerates everything at exactly the same rate.
Continue reading A Bowling Ball and Feather Falling in a Vacuum (video)