You can’t see the Great Wall of China from space

It’s an often quoted myth but it is not true at all that the Great Wall of China can be seen from space. From up high, above the atmosphere, it’s possible to see city lights and also, according to this Popular Mechanics article, the vast greenhouses of Almeria, in Spain. The Great Wall of China is really rather long (over 6000km) but it is also very narrow, on average about 6 metres wide (ranges from 5m to 9m) and doesn’t stand out much from its surroundings. To be able to see it from near-earth orbit (160km up) you’d need to …

Continue reading

6 surprising facts about the moon

There is no dark side of the moon, really. As a matter of fact, it’s all dark. The only thing that makes it look light is the sun. Gerry Driscoll, Pink Floyd, “Eclipse”, The Dark Side of the Moon. The moon is the only natural satellite of the planet we call home. It is much smaller (27% the diameter of the earth) and less dense (60% of the density of the earth) which makes it just 1.2% of the earth’s mass. It is also the second brightest object in the sky, after the sun. Here are six interesting facts about …

Continue reading

Does coffee make you poop?

As I sit here, holding a half-finished cup of coffee, I can already feel the internal rumbling. Soon, I will go to the toilet and do… my business. I’m sure you’re glad I told you that. Who wouldn’t want to know about my bowel movements. This is the internet, after all. But is the coffee responsible? Or is it psychological? Does coffee really make you poop?

If there are infinite stars, why is the sky dark at night?

Go outside tonight and look up into the sky. What do you see? A bunch of bright points in the sky: the light from far away stars (unless you’re in Britain, in that case the sky will probably be cloudy). But most of the sky is dark. Even if you go somewhere with very little light pollution (like the middle of the Sahara desert, for example) the sky will be dark. Sure, you’d be able to see more stars more clearly and observe the milky way in all its glory but the sky will definitely not  be as bright as …

Continue reading

Can too much water kill you? And should you drink 8 glasses a day?

All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy. – Attributed to Paracelsus (1493-1541) Let’s start with cliché. Water is life. Well, it’s not actually life itself (it is, after all, just a molecule), but  it is fundamental to carbon-based life forms such as us, bacteria and everything else that we consider to be living. So important that we first look for liquid water on other planets to determine the possibility of extra-terrestrial life. However, as our long dead friend explained above, anything can be bad for you taken …

Continue reading

Should you rinse soapy dishes – How soap works

I’ve been traveling in the past few weeks, as you may have noticed from the lack of articles. This week I’ve been visiting friends in Germany. To be a good guest, and less of a burden on my hosts, I’ve been helping out with the daily chores, including washing the dishes. And, as it turns out, my friends and I are split into two camps. Those who rinse dishes after soaping them up and those who don’t. And to show you how those in the second camp are clearly and utterly wrong, we first need to understand how soap (or …

Continue reading

How can human fluids be sterile? – There are no bacteria “inside” the body

Gut flora, the bacteria inside human’s digestive tract, performs a fundamental role. Without it, humans would not be able to digest a large variety of food (including complex carbohydrates). And there are a lot of these bacteria: they compose up to 60% of the dry weight of faeces. There are also a lot of bacteria on human skin. The number of bacteria on the skin of the average person is about 1 trillion. Which is a lot. Yet, bodily fluids (like blood, urine, cerebrospinal fluid, etc.) are considered sterile (while still inside the body). How is this possible, when there are …

Continue reading

Maps are all lies – Representing a spherical earth on a flat world map

Is Greenland really bigger than Africa and Australia?  Take a deep breath.  The big map in your high school classroom, the atlas you’ve used to navigate during a road trip and even google maps are all lying to you. They all start with the same big lie, that the earth is flat, two-dimensional, like a pancake. When in fact, as humans have known for a very long time, at least since the time of ancient Greeks, that the earth is spherical (that people thought that the earth was flat at the time of Columbus is a myth). Well, not exactly spherical, …

Continue reading

Whatever happened to the hole in the ozone layer?

We are all very familiar with global warming, a predicted ecological disaster that we’re still figuring out how to deal with (and also struggling to convince some people of its existence and importance). But if you’re a bit older, you might remember that there was another quite talked-about ecological disaster caused by humans: the depletion of the ozone layer (sometimes people conflate global warming and ozone depletion but they are two different phenomena caused by different types of man-made pollution). Back when I was a bit younger it was big news. UV rays are nothing to be trifled with. So …

Continue reading

How much water would you need to put out the sun?

The sun is a giant ball of gas that burns at the centre of the solar system. And the adjective giant is not unearned: the sun constitutes 99.86% of the mass of the solar system. Without it life as we know it would not exist. Water would not be liquid. Plants would not be able to photosynthesise. Without the sun the earth would just be a big icy rock floating through interstellar space. But let’s assume you have a death wish and want to try to put it out. How much water would you need?