Archive for the ‘science’ Category

On the cenotes of the Yucatan Peninsula
March 8, 2019

A cenote close to the ancient Maya city known today as “Ek Balam”.

A cenote close to the ancient Maya city known today as “Ek Balam”.

I only learned about cenotes a mere weeks before I set foot on that magical country called México – what they are is quickly explained, but there is a much more profound story behind them than that they make for spectacular swimming pools or even that the ancient Maya apparently included them in sacrificial ceremonies.

Cenotes are natural sinkholes and they are the result of collapsing limestone ceilings – relatively soft rock from right below the earth’s surface. There are innumerable examples of sudden sinkhole breakaways all over the planet and even though that does sound like adventurous, it can turn out quite catastrophic in urban areas.

One such example was the 2007 sinkhole in Guatemala: Here, a 100m deep sinkhole was formed in the capital city’s northeast, in the middle of a poor neighbourhood; 5 people lost their lives and about a thousand needed to be evacuated.

The ‘city cenote’ within the charming town of Valladolid (in Yucatan State).

The ‘city cenote’ within the charming town of Valladolid (in Yucatan State).

Now, in the Yucatan Peninsula there are about 6,000 sinkholes (or cenotes) of varying sizes – most are reasonably small, but some are large enough to serve as a decent pool (and a favorite tourist attraction). Cenotes connect the planet’s surface with underground water bodies and that means mostly very clean fresh water. This was especially important for the ancient Maya since there are almost no rivers or lakes located on the peninsula.

So what is so interesting about the cenotes in that specific region? The Yucatan Peninsula is most famous among geologists for the location of the Chicxulub crater that was formed by the impact of either an asteroid or comet about 66 million years ago. That impact was a dramatic one and most likely responsible for a mass extinction including the disappearance of non-avian dinosaurs (today’s birds are the descendants of flying dinosaurs) which gave rise to populations of small possibly mouse-like mammals – our ancestors. However, it is estimated that about 75 % of all flora and fauna species then present on the planet became extinct.

The location of the Chicxulub crater in the north of the Yucatan Peninsula (the center being close to the town that gave the crater its name: Chicxulub).

The location of the Chicxulub crater in the north of the Yucatan Peninsula (the center being close to the town that gave the crater its name: Chicxulub).

The following map of the crater impact structure reveals a striking concentration of cenotes around the crater rim (represented by white dots; the white line shows the coastline). These sinkholes can not only be as deep as up to 100 metres, they are actually connected by a vast network of underwater cave structures. And these were most likely formed by the asteroid’s (or comet’s) tremendous impact that would change the face and shape of the planet until today. Keep all this in mind next time you jump into one of those wonderfully refreshing natural wonders!

The so-called Chicxulub ‘impactor’ had an estimated diameter of between 11 to 81 kilometres. As a result it carried the energy of about 21 to 921 Hiroshima Atomic bombs causing a 100 m high tsunami.

The so-called Chicxulub ‘impactor’ had an estimated diameter of between 11 to 81 kilometres. As a result it carried the energy of about 21 to 921 Hiroshima Atomic bombs causing a 100 m high tsunami.

Click here for a visual animation of the Chicxulub impactor on the Yucatan Peninsula.

At the Centre of the Rainbow Light Circle
December 22, 2018

Double rainbow on our third summer roadtrip (August 2016) – as seen in the Masuria region of Northern Poland.

Double rainbow on our third summer roadtrip (August 2016) – as seen in the Masuria region of Northern Poland.

I’m writing these lines after a day full of sightseeing lying in my hostel bed in Saigon, Vietnam. In stead of coming up with Vietnamese travel tales, however, this is going to be a different sort of post – not really about traveling at all, but rather about the magic of reality (but traveling often enough covers both: magic and reality).

This post is largely inspired by the fabulous sixth book of British evolutionary biologist Richard Dawkins, called Unweaving the Rainbow. In fact, this post is about exactly that: unweaving rainbows, metaphorical so, but also quite literally. To begin with: Dawkins wrote the book as a response to the claim that science would “take away” from the magic of reality, that it would diminish the view of the world – wrapping it up with some sort of sober and overly rational scientific blanket. Dawkins argues quite the opposite: Unweaving the rainbow does not diminish the imagination, it actually enlarges the picture as a whole: To actually grasp what a rainbow really is and what else there is to it is not only marvellous, it can be quite mesmerising. And that is what this post is about.

A rainbow as seen from the windows of my flat in Berlin-Friedrichshain.

A rainbow as seen from the windows of my flat in Berlin-Friedrichshain.

So we all know how a rainbow comes into being, right? In short: It is caused by reflection, refraction and dispersion of light in droplets of water in the sky. When caused by the light of the sun a rainbow always appears in the opposite part of the sky. This is because the back surface of raindrops (which are roughly spherical) act as concave mirrors. The lower the sun, the higher the rainbow, but if the sun is higher in the sky than 42 degrees above the horizon we can’t see a rainbow at all. (This is why we see rainbows usually in early morning or late afternoon.)

So the light of the sun hits the rain droplets’ concave walls, then gets reflected, leaves the drops and will land at your eyes, but not before being refracted while moving from water back into air. We see the complete light spectrum (from red via yellow and green to violet) because there are so many raindrops, enough for all the colours to hit your eyes.

Steep rainbow curve as seen in Bergen, Norway in September 2018.

Steep rainbow curve as seen in Bergen, Norway in September 2018.

Now, the fascinating part (something I never really bothered pondering about, but it is really quite worth it). All those different raindrops being able to perform a complete spectrum for you to see from whatever angle means something else as well: The rainbow you are seeing is slightly different all the time, depending on your position. It is not only different for every single being who sees it, it is (consequently) also different for each of your eyes. You are always standing at the centre of your personal rainbow, piecing it together from different collections of raindrops. (So everyone around you is always positioned at the centre of their very own rainbow).

And when you are staring at a rainbow while sitting inside a car or train you do not actually see “the same one” rainbow, but a steady series of rainbows in quick succession.

“Observe the rays of the sun in the composition of the rainbow, the colours of which are generated by the falling rain, when each drop in its descent takes every colour of the bow.”

(Leonardo da Vinci, Treatise on Painting in the 1490s)

Every colour of the bow, Leonardo remarks – but a bow, really? The classic romantic portray of the rainbow is caused by the illusion that it is always pegged far away at the horizon, impossible to approach. But a rainbow only appears as a semicircle (or bow) because “the horizon gets in the way of the lower part of the circle” as Dawkins puts it.

Red rainbows (and sometimes even monochrome rainbows) are possible when the colours with shorter wavelengths like blue and green are scattered and thereby removed from the spectrum.

Red rainbows (and sometimes even monochrome rainbows) are possible when the colours with shorter wavelengths like blue and green are scattered and thereby removed from the spectrum.

So when we see a rainbow, we are in fact merely seeing a part of the whole. And the reason it appears to be so huge (and hence far away) is that our brain is playing tricks: It projects the image we receive with our eyes “outwards on to the sky” (Dawkins), an effect easily being imitated by staring into some bright light (e.g. a lamp) and stamping the after-image on your retina before projecting it onto the sky.

So how can we see an actual full-circle rainbow? The largest section of the rainbow we would be usually able to see is about 50 % at either sunrise or sunset. In order to see the rainbow’s lower half there would need to be raindrops below the observer’s horizon plus sunlight that reaches them. This can be achieved by watching a rainbow either from a (very) high building or an airplane.

It is easy to create a (little) full-circle rainbow yourself by creating a water mist e.g. with a garden hose while facing away from the sun.

Note the reversed colours of the fainter upper rainbow.

Note the reversed colours of the fainter upper rainbow.

Why are there double rainbows? One not seldomly sees an additional (yet fainter) rainbow (at 8 degrees higher than the first and with reversed colours) which happens when light enters the raindrops both through the upper and the lower quadrant – under the right conditions the light can then “be reflected twice round the inside of the sphere” (Dawkins).

So much for rainbows on blogposts from my side! Keep all that in mind the next time you happen to experience a double rainbow (and possibly a monochrome one).

If you want to get to know more about what else there is to be unwoven I can only recommend to get a copy of the book mentioned in the beginning (see picture below). I will end this post with the following (highly enchanting) words by Richard Dawkins while celebrating the birthday of a dear friend of mine. Thank you for inspiring so many of my days. Much love to you!

“We are going to die, and that makes us the lucky ones. Most people are never going to die because they are never going to be born. The potential people who could have been here in my place but who will in fact never see the light of day outnumber the sand grains of Arabia. Certainly those unborn ghosts include greater poets than Keats, scientists greater than Newton. We know this because the set of possible people allowed by our DNA so massively exceeds the set of actual people. In the teeth of these stupefying odds it is you and I, in our ordinariness, that are here.”