Sometimes, writes Brian J Ford, well-intentioned efforts to bring science to the public can come to grief...

Last week on ITV, the perky and bright Becky Mantin popped up to give her weather report. First, though (while we were all waiting for the forecast) she gave her explanation of rainbows.

They happen, she said, because of the way that light is refracted through a raindrop. Fair enough, you might think, but her explanation fell into a trap. Her raindrop was shown as a cartoon teardrop – pointed. Yet no raindrop, anywhere in the world, since the dawn of time, has looked like that. Raindrops are round. They’re perfect little spheres, and never pointed.

The largest ones become slightly flattened, like a hamburger bun, but they’re never that teardrop shape. If they were, the refraction wouldn’t work, so there would be no rainbows at all.

She could have mentioned double rainbows, which thousands of people have recently seen. What’s interesting is that the colours are inverted in the faint extra rainbow, with red on the inside (normally, red – being the longest wavelength – is at the top).

Yet even the best resources get those the wrong way round. There’s a graphic online that offers you a “realistic rainbow” to add to your photo. It’s posted by the multibillions-worth Adobe Inc. And has all that money guaranteed reliability? Not really – their rainbow is inside out.