Tag Archives: rainbow

Rainbows in regnbyen Bergen

Yesterday when approaching Bergen airport, I saw something super cool: The lower half of a rainbow!

Even though I grabbed my phone and snapped a picture in record time, I didn’t manage to capture it. Bummer! But that doesn’t keep me from writing about it while showing you a “normal” rainbow I took a picture of a couple of minutes later.

Rainbow seen from a plane approaching Bergen airport

Rainbow seen from a plane approaching Bergen airport

Have you ever seen the lower half of a rainbow?

But can you imagine it? A u-shaped rainbow?

Have you ever seen anything like that before? It’s not something that we are used to seeing, at least not if we are looking a) at rainbows that are occurring on natural rain “curtains” and b) while we are on the ground. Let me explain…

Under perfect conditions, a rainbow is a full circle

Imagine you are a floating in space, looking at a curtain of rain drops. The sun is shining from behind you onto that curtain. What you then see on that rain curtain is a full rainbow circle, purple towards the middle and red towards the outside.

The size of the rainbow depends on how far away from the rain curtain you are. Imagine looking at the shadow that your head is making on the rain curtain. The line from your eyes to the shadow of your head will be our reference. Now imagine looking at any point on the rainbow. The line from your eyes to any point on the rainbow will be at a 40 to 42 degree angle to the reference line (40 degrees if you are looking at a purple point, 42 if you are looking at a red point, anything in between for the other colors).

Tweaking the size of the rainbow

Now imagine moving the rain curtain farther away. The angle between the reference line and the line to the rainbow stays the same, but the further away the rain curtain, the larger the rainbow. And vice versa: The closer the rain curtain, the smaller the rainbow!

So now imagine a nice curtain of droplets that you can walk towards and away from (sprinklers! garden hoses!) — the further you walk away, the larger the rainbow gets. And the closer you come, the more it shrinks again.

Standing on the ground, you only see the upper half

If you walk close enough to the rain curtain, you can actually see a full rainbow. But typically when we think of rainbows, we think of those occurring naturally, and then the rain curtains aren’t as neat and tidy as those from a sprinkler, and rainbows that we see are usually far far away, and thus really big. And that is why we aren’t used to seeing the lower half of a rainbow: Where the lower half would be there isn’t any rain curtain for it to appear on, because there is ground there! And the only way not to have the rainbow hit the ground is either have it close enough in front of us so it’s too small to even reach the ground, or to look at it from a plane that is high enough above the ground that even a large rainbow has enough space above the ground to fully appear on the rain curtain.

Next steps

So where do we go from here? I need to a) play with sprinklers and take pictures of rainbows! b) draw illustrations of the stuff I tried to describe above, and c) hope that I’ll be faster next time to finally get my u-shaped rainbow picture from a plane!

Alexander’s band: the dark space in between a primary and secondary rainbow

Bergen is a fairly wet place with on average 240 rain days every year. But that actually provides us with the perfect opportunity to see plenty of rainbows. Here is the view from the window of my apartment in the university guest house yesterday (and I love the raindrops on the windowpane!):

Bergen, Norway: primary and secondary rainbow on August 17, 2018. Note the "Alexander's band", the dark space between the two rainbows!

Bergen, Norway: primary and secondary rainbow on August 17, 2018. Note the “Alexander’s band”, the dark space between the two rainbows!

Isn’t this beautiful?

I am always fascinated by the intensity of the colors in a rainbow, and in cases where you get a primary and a secondary rainbow, of the darkness between those two. That area is called “Alexander’s band”, and occurs because the inner, primary rainbow focusses light towards its inside, whereas the outer, secondary rainbow spreads it towards its outside. So we end up with this dramatic dark band in between the two. I love how dramatic it looks!

Bergen, Norway: primary and secondary rainbow on August 17, 2018. Note the "Alexander's band", the dark space between the two rainbows!

Bergen, Norway: primary and secondary rainbow on August 17, 2018. Note the “Alexander’s band”, the dark space between the two rainbows!

Fun fact on the side: A couple of years ago I did a couple of short movies on optics in rainbows, when I was playing around with different styles of teaching videos. Watching them back today is so painful, but at least this blog helps me to remember how far I have come… ;-)

But let’s get back to talking about the weather. As I learned during the “summer concert” of the Bergen Filharmoniske Orkester yesterday: According to conductor Edward Gardner, translating from Det finnes ikke dårlig vær, bare dårlige klær, “there is no such thing as bad weather, only bad cleather”. Hahaha.

Summer concert of the Bergen Filharmoniske Orkester under conductor Edward Gardner on August 17, 2018. On the big screen you get a glimpse of what the weather was like...

Summer concert of the Bergen Filharmoniske Orkester under conductor Edward Gardner on August 17, 2018. On the big screen you get a glimpse of what the weather was like…

Above, on the big screen behind the orchestra, you see the kind of clothing that was appropriate for the occasion. That was one brilliant concert and totally worth sitting in the pouring rain with rain coat, rain pants, waterproof shoes! There really is no such thing as bad weather! :-)

A touristy post about my trip to Heligoland

I recently went on a trip to Heligoland, Germany’s only island that is far away from the mainland (70 km in this case). It was a great trip, and I know you’ll be reading about it for some weeks to come :-)

Today, we’ll just do the touristy parts, though, and get into the oceanography later.

The trip started out super awesome. I went on a ferry and got the chance to see ships being greeted by Wilkomm Höft, the Ship Welcome Station, by dipping the Hamburg flag and playing the national anthem. I’ve seen this before, but only from land (this is a place that I love going to for birthdays, mine and other people’s). Sitting on a ship and being bid farewell this way is really touching! I loved it and got a little teary-eyed.

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Being bid farewell (by dipping the Hamburg flag and playing music) at Wilkomm Höft in Wedel on the Elbe river.

The ferry itself is a high speed catamaran, which, as you might have guessed, produces an amazing wake.

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Wake of the Halunder Jet, the high-speed ferry going from Hamburg to Heligoland.

Unfortunately, the ship is set up such that the rescue boats obscure the view of the wake a little. How inconsiderate ;-) Please ignore the outboard engine…

On Heligoland itself, there are the famous red cliffs, and tons of birds. Let me just show you a few:

Heligoland

Heligoland

The best-known part of Heligoland is the Lange Anna — a red rock called “long Anna”. You see it on the picture below. What I liked most about it — besides the beauty of the rock and the birds, obviously — was the wave breaker build there to protect the coast, and what it did to the waves.

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“Lange Anna”, the famous red rock on Heligoland in the German Bight

Zooming in on the wave breaker’s edge, there is clearly very strong winds coming around that corner:

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To be fair, it was a super windy day.

They also have a very nice beach on Heligoland, where you can see the bending of waves due to changes in topography that we talked about before.

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And if you look over to the second island, you can very nicely compare and contrast the upwind and downwind coasts of islands:

See how there are lots of breaking waves (well, you probably only see the foam) on the upwind coast of the island in the back of the image, and how there are absolutely no waves in the lee of the sea wall in the foreground of that picture?

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Btw, the downwind side of that same second island looks also a lot calmer as it is sheltered by the island itself:

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Unfortunately, I couldn’t take a picture of the whole island at once, I really need to upgrade my camera… But can you spot the rainbow above?

Also there is some more, pretty spectacular weather to be seen:

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If you go over to the other island, there are TONS of seals. Like several hundred, right on the beach! Obviously, I only have pictures of seals when there are also nice waves happening at the same time :-)

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Oh, and birds.

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And more seals! This one is cute, I have to admit…

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Oh, and I was lucky (lucky means bold enough to ask!) enough to hitch a ride on the local research vessel, Aade. Below, they just finish a plankton trawl. We weren’t allowed out on deck because the weather was so rough…

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What looks like a calm and serene morning really wasn’t one. It was super windy and wavy! Good thing I don’t get sea sick.

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It turns out it’s super difficult to take pictures of waves that look as impressive as the waves are in reality. I really need to learn how to do that! But even if you don’t see the size of the waves, at least you get a different look at “lange Anna” below.

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And these are white caps on the “open” sea, not waves breaking on a shore.

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And for a nice comparison: The Aade (the research vessel I was on) and the catamaran that took me home later that night.

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Anyway, it was a great trip!

The difference between secondary rainbows and double rainbows

More reflection or more rain?

Ha, aren’t you enjoying talking about optics again?

Sometimes you see two rainbows that both have red on the outside and blue on the inside. And according to my post on secondary rainbows, that should not be the case. Yet is has been observed. Why?

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Rainbow and secondary rainbow, seen at Heathrow Airport. Picture by my friend F.

As you remember, secondary rainbows form outside the primary rainbows because the light is reflected twice inside the raindrop rather than only once as in the case of a primary rainbow. But that second rainbow with red on the outer rim and blue on the inner is formed differently.

Until now we’ve assumed that all the rainbows appear on the same rain front. This is not the case for the rainbow we are talking about here – it is formed on a second rain front behind the first one. So the path of light within rain drops of both rainbows on both fronts is similar, with light being only reflected once for each rainbow.

When you google double rainbows, you sometimes find pictures of two rainbows, both with red on the outer rim, nicely separated from each other. And when you see those pictures, you can be pretty sure that they’ve been photoshopped. Double rainbows of the kind we are talking about here overlap, and usually you see one full rainbow with all its colors, and then a slightly smaller rainbow with only green, blue and purple peeking out:

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If you look closely, there is a green-and-purple band on the inside of the complete rainbow. Double rainbow!

Sun dogs

Recently spotted: sun dogs, a special form of halo! Or rather sun dog (singular), since there was only one to be seen and not a second one at equal distance from the sun but on its opposite side.

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Sun dog spotted somewhere between Mölln and Hamburg

These pictures are exactly as my camera took them without any filters or color enhancement or anything. Isn’t it weird that we appeared to be the only car stopping every couple of minutes to watch while everybody just continued driving?

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Sun dog spotted somewhere between Mölln and Hamburg

Rainbows and prisms

Lets go back and talk about one of my favorite non-oceanographic topics: Rainbows!

When I had my rainbow phase about a year ago, my mom sent me the movie below, which shows what you see when you look directly into the prism that paints these kinds of rainbows all over my parents’ living room:

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Rainbow from glass prism

When you look directly into the prism, you don’t see a rainbow like the one projected on the wall, but you see one color at a time. Only as the prism moves you experience all the different colors of the rainbow. And that is interesting because in a rainbow you see all colors at once, yet here you don’t. This is going to go into the next version of my rainbow movie, but for now check out my mom’s:

My renewed interest in rainbows was sparked one Saturday where I saw one on my way to the swimming pool in the morning.

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And then a double rainbow on an evening walk with a friend.

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And then another friend, F., sent me the picture below which he had taken at Heathrow and which he kindly allowed me to use for educational purposes on my blog.Screen shot 2015-06-07 at 8.09.47 PM

Are you as exited as I am that we are finally getting back into rainbows? :-)

What are the ingredients of a rainbow?

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?

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

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!

Secondary rainbows

Sometimes you get lucky and see a double rainbow. But how does the second rainbow form?

On my first 17th of May in Bergen, Ellen invited me to her home for a traditional dinner, which was exceptional. And as a bonus we got to see a double rainbow over Store Lungårdsvann!

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Double rainbow in Bergen on May 17th 2011

The outer rainbow is the so-called secondary rainbow, and as you can see the colors in the secondary rainbow are reversed, with red being on the inside and blue being on the outside.

Having watched my explanations in the textbook-style movie or in the short movie collection, is the sketch below enough information for you to make sense of how a secondary rainbow forms?

If the sketch isn’t clear – what additional information would you need to make sense of the sketch?

Here comes the movie in case you’d like to watch it:

I have yet a newer version of the rainbow movies as well as the one pictured above ready for you, but I thought I’d give you a bit of a break from rainbows and talk about something else for a while. But we’ll be back to rainbows soon, promise!