LIGO detects gravitational waves from neutron star merger

Carl Sagan’s famous quote says “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” In that famous quote, Sagan makes reference to the whole universe started off with hydrogen and helium, all […]

Why do we see only one side of the Moon?

You have probably heard references been made to the “dark side” of the Moon – there’s even a Pink Floyd album with that name. But, in fact, there’s no “dark side” of the moon. Because our satellite is not illuminated by the Earth, it is illuminated by the Sun. All the surface of the moon gets lit by […]

Why astronauts float in space

We see images and videos from the International Space Station (ISS) where astronauts floating in the space freely. That’s because they’re in the space, so there is no gravitational force of Earth there, right? Wrong. The International Space Station is in Low Earth OrbitSee notes 1 with an altitude of between 330 and 435 km […]

How Eratosthenes calculated the Earth’s circumference

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 […]

Are we the first?

In 1950, the Italian physicist Enrico Fermi was chatting with his colleagues at the Los Alamos National Laboratory(1). They talked about the recent rise in UFO reports, then the conversation shifted to other subjects. But during lunch, Fermi suddenly asked: “Where is everybody?”. He was talking about extraterrestrial life, especially intelligent life. He made some […]

Your Life On Earth (presented by BBC)

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.

No! The Earth Would NOT Look Like This Without Water

No, no no, and again: no! The Earth would NOT look like this without water. Please stop sharing this nonsense. Here some numbers: the Earth has a diameter of about 12,735 kilometers (on average). The highest point on Earth is the top of Mount Everest, at 8,848 meters (29,029 feet). The deepest point on Earth […]

A Bowling Ball and Feather Falling in a Vacuum (video)

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 […]