10 Things You Maybe Didn’t Know About Rainbows

Science correspondent David Bradley describes some interesting facts about rainbows that you may not have known:

I am currently reading the most excellent “The Sun’s Heartbeat” by astronomy writer Bob Berman. It’s the kind of book I’d love to be able to write, informative, entertaining, engaging and witty. In it, Berman explains the solar things you may always have wondered about from total eclipses (far more astounding than any partial) and sun spots to the inner sun and the secrets of rainbows. Rainbows you will remember are formed by the refraction of sunlight through water droplets in the sky, what is more they don’t exist…without you. Every rainbow that ever there was there because someone glanced up and saw it. But, rainbows are even more strange and weird than that cynical glance might suggest. Here are Berman’s 10 things you probably didn’t know about rainbows:

1 Rainbows are seasonal, being observed late on summer afternoons and extremely rarely in winter

2 You will never see a rainbow if the sun is more than half way up the sky, so you won’t catch sight of one between 9am and 4pm in early summer

3 If the sun is low, the rainbow will be brighter and the colours deeper

4 The sky above a rainbow is much darker than the sky within its arc

5 The top of a rainbow can never be higher than 42 degrees from ground level, such high rainbows seen at sunrise or sunset lack depth in the blue part

6 The ends of a rainbow stop at the ground only because that’s where the rain stops. A rainbow at a waterfall can form a full circle 82 degrees in extent

7 Double rainbows are not that rare. The second bow appears 9 degrees outside the main bow and the colours are reversed. A third bow within the first is never formed but you might see alternating green and pink fringes (non-spectral colours) known as supernumerary arcs

8 The gap between a primary and secondary rainbow will be darker than the rest of the sky, this is Alexander’s dark band, named after Alexander of Aphrodisias (a great factoid for taking on a date, perhaps?)

9 Rainbows are like vampires, they have no reflection and cast no shadow. If you look at a rainbow in a mirror, it’s a different rainbow

10 Every rainbow is an arc, part of a circle and at the centre of the circle is no pot of gold, but something quite shocking. Think about it. The sun is directly behind you, the rainbow lies on an arc parallel to the base of a cone the apex of which is the point at which you stand. So, what’s at the centre of a rainbow? The shadow of your head, of course!

This article has been reproduced from Sciencebase Science News. Copyright David Bradley.

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About David Bradley Science Writer

David Bradley has worked in science communication for more than twenty years. After reading chemistry at university, he worked and travelled in the USA, did a stint in a QA/QC lab and then took on a role as a technical editor for the Royal Society of Chemistry. Then, following an extended trip to Australia, he returned and began contributing as a freelance to the likes of New Scientist and various trade magazines. He has been growing his portfolio and and has constructed the Sciencebase Science News and the Sciencetext technology website. He also runs the SciScoop Science Forum which is open to guest contributors on scientific topics.
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