Category Archives: observation

Diffraction of light

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Today I’m playing with the sun.

As I mentioned in the sun dog post already, I recently went on the ferry from Kiel to Gothenburg. And I had plenty of time to watch the sun rise and set.

One thing that kept me entertained for quite a while is to squeeze the sun through the imaginary eye in the mast:

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As the sun moved behind the mast (or as I moved in front of the mast, whatever), the sun seemed to get pinched in while passing.

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Watch the video below to see the whole thing in action:

Also highly entertaining: Watching how the sun eats into my finger tips as I bring them together in front of the sun:

Kids. If you try this at home, please make sure you only look at the sun on the display of your camera, never look directly into the sun…

Tidal elevations and currents in Fowey, Cornwall

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Tides in Cornwall.

The other day we talked about a very simplistic models of tides in a glass, and how the high tide and low tide travel as a wave around an ocean basin. This isn’t really a news flash for people reading this blog, I know. But it is sometimes hard to imagine how big the differences between high tide and low tide actually are, since the water rises and falls so slowly it is hardly noticeable.

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Fowey harbor in Cornwall at high tide

On my most recent holiday (even though “most recent” means “some time during summer”, which is actually quite a while ago), A and I stayed in Fowey and had the best time. Anyway, we happened to stroll along the pier, and I happened to snap this picture.

Some more strolling happened (and we might or might not have had Cornish Cream Tea), and six or so hours later we were back in the same spot, to see this:

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Fowey harbor in Cornwall at low tide

The water was gone! And I still find it absolutely fascinating.

Especially since at first glance the tides don’t seem to result in alternating currents. Which is really not possible.

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Fowey harbor – incoming tide

But it took more than just a second look to realize that the tide in the picture above is coming in, whereas the one below is going out (Pictures taken from pretty much the same spot).

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Fowey harbor – tide is going out

You can only see that if you look at the moored sailing ships far across the water. The colorful boats always face out towards the sea – because they are moored between two moorings and are not turning freely around a single mooring as I had assumed they would. Duh! But for the yachts in the background it is clear they are only moored in one spot: They face right on the upper, and left on the lower picture. Yep, those are the kind of things that fascinate me while I’m on vacation! :-)

Sun dogs

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More refraction of light.

Recently I found myself on the ferry from Kiel to Gothenburg, watching the sun rise.

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Next to the sun, I noticed a piece of a rainbow.

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Now as we all know, rainbows are supposed to only be visible when we are facing away from the sun. Clearly not the case here.

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By the way, I’m talking about the rainbow-y thingy to the right of the sun, the spec close to the sun is probably something on the lens of my camera, or some other artefact of some sort.

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So I read up on the rainbow-y thingy, and apparently it is called a sun dog.

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There are supposed to be two of those, on either side of the sun.

IMG_9494Do you know those medieval pictures of three suns, with the outer two facing the inner one? Apparently those are supposed to be sun dogs! I never knew.

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Anyway, I stood, fascinatedly watching the rainbow-y thingy.

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Occasionally distracted by cool ships.

IMG_9522The higher the sun rose, the more colorful the rainbow-y thingy became. While it had been colorful for the naked eye (ok, I’m wearing glasses, but you know what I mean. No filters or polarization or anything), it started to show up on pictures, too.

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In the beginning I tried finding the second sun dog on the left of the sun, but there was nothing. But the one on the right got prettier and prettier!

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Eventually we arrived in the port of Gothenburg and I got distracted by container terminals and other exciting things that you will surely hear about very soon.

IMG_9551But for now I’ll leave you with this amazing view of the little islands right before you enter Gothenburg. Ready for a Scandinavian holiday? :-)

 

Awesome fountain Birmingham

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Because water is endlessly fascinating.

As those of you who know me in person are acutely aware – I am traveling too much right now. Hence the content on this blog is a little thin right now, at least on the experimental side. Difficult to run a lot of awesome experiments when at conferences (although we did manage at EMSEA!). But I will come back to more experiments soon (plenty of things in the pipeline!!!) and the great thing is that as I travel, I get to see lots of cool places with even cooler water features.

So today I’m sharing something I saw at the ThinkTank science museum in Birmingham, UK: an amazing fountain. Enjoy!

 

Trajectories of a projectile

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And you know me – it had to be a projectile made of water.

The shopping mall where I live has some really nice water features that I always get fascinated by, so I had to share. My favorite one is the fountain in the picture below (and if it is too hard to see in the pictures, there is a movie at the bottom of this post).

It doesn’t look terribly spectacular here, but the really nice feature is that the water sometimes goes in short bursts.

In the picture below, for example, you see a moment where the water has stopped, but there is still quite a lot on its way.

You can watch it falling, and you see that on the right, the next burst is starting.

What I find so fascinating is that the short bursts of water visualize the trajectory so much more clearly than a continuous stream of water does, and also than a flying ball would. It almost gives the impression of being slow motion, even though of course it is not.

If I were to teach introductory physics any time soon, I would make a really nice teaching unit out of this one. But for now I’ll leave you with a movie:

Lighthouses and Fresnel lenses

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Or more reasons for why I want to live in a lighthouse.

I have always been fascinated by lighthouses. Always. Usually because they are built in the most wonderful places and I would just love to live there. For example one near San Francisco that has this view:

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Golden Gate Bridge

But then also because they can cast their beams of light over such long distances, even though they look perfectly harmless during daytime:

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Close-up of the same lighthouse as above

So this is what the inside looks like (pictures taken at the ThinkTank science museum in Birmingham, UK):

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The insides of a lighthouse

And the whole thing is only lit by a tiny lightbulb!

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And there is just a tiny light bulb on the inside!

Watch the movie below to see how the light is focused by the Fresnel lenses. Really fascinated how the light bulb is surrounded only by glass, but still the light is focused really sharply.

I have a Fresnel lense that I’ll play around with soon, so stay tuned for more on cool optics! :-)

What are the ingredients of a rainbow?

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Still collecting materials for our instructional short movies.

A while back I talked about how my colleague and I were experimenting with short instructional screen casts, and I shared some first attempts at movies on how rainbows form. We are still working on a story board for an improved version, but I was lucky enough to see a very pretty rainbow in a fountain the other day.

The picture below is a good demonstration of how rainbows form where there are water droplets in the air (provided there is enough sunlight, too, and we are watching from the right position) – we still see a bit of the rainbow to the right of the fountain, even though the wind direction has changed and the fountain is now blown to the left, visible because of the mist and the lower part of rainbow.

Fascinated as I was I had to film clips of this, too, which are combined in the movie below. There you see the rainbow appearing and disappearing, depending on where the fountain is moved by the wind, i.e. whether it is moved to the part of the sky where all the angles are right for us to see a rainbow, or not.

It was a magical moment – enjoy! :-)

Why do we only see rainbows in the mornings and evenings, but never at noon?

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Another movie on rainbows

My dearest readers, I hope you are still as fascinated by rainbows as I am? Today I’m giving you another movie explaining something rainbow-related, namely why we do not see rainbows when the sun is too high up in the sky. The video is stylistically similar to the ones I did before, and while practice really helps and I am getting pretty fast in making this kind of videos now, I am ready to try something new. But using doceri is something that I could imagine doing operationally if I was to use this kind of movies in my courses. It is really a nice tool!

So here is my movie. As always, let me know how you like it and what I could do better!

P.S.: Whenever I say or write 82, what I mean is 84! But according to my colleague it is actually beneficial to learning if movies aren’t perfect, because hesitation or small mistakes create irritations in the learner, which then make him think about what you were saying. And as the learner is now engaging more actively, the learning process is more successful. So there you go! :-)

Rainbows III

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Updated movie following Arne’s advice.

When I asked for feedback on the rainbow movies the other day, Arne had a pretty good idea for how one of the explanations could be made more intuitive. I have other people’s comments still in the queue and I’m working on them, this is still very much in the trial & error phase… And unfortunately it’s in german, which I didn’t realize until I had uploaded it.

But please do keep the comments coming, I will include them eventually!

Sun halo

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A rainbow that isn’t one, technically speaking.

Browsing through the photos on my phone, I came across the one below that I took two years ago in Bergen. I remember taking the picture with Nadine on our way home, and wanting to look up what phenomenon caused this ring around the sun, but I never did – until now.

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Halo in Bergen

So, according to Wikipedia and various other internet sources, what we see in that picture is a 22° halo. In contrasts to rainbows which you see when you are facing away from the sun, this kind of halo forms as a circle around the sun. Also in contrast to rainbows, in this case sun rays aren’t refracted at raindrops, but at ice crystals. Since ice crystals typically have a hexagonal shape, this causes the radius of the halo to be on average 22°. On average, since refraction still depends on the wavelength of the refracted light – hence the halo is red-ish towards the middle and blue-ish towards the outer rim. This is also different in a rainbow, where the outer rim is red and the inner rim is blue.

Why is that? Stay tuned for the next posts, I’m still trying to figure out a good explanation. For those of you who saw my post on teaching videos a week ago, you might have noticed that I was working on something related to refraction and reflection and light already then… ;-)