Chartham Downs, near Canterbury.
Don’t bother looking around midday – A rainbow cannot form if the sun is directly overhead. Your best bet is to look for them before 10am and after 2pm. (Possibly before 11am and after 1pm in winter when the sun’s lower)
Always have your back to the sun as the rainbow will only be created opposite the source of light.
You need a convective atmosphere – so a showery situation. You’re unlikely to see one with a passing weather front as there’s often too much cloud and rain to see the sunshine (unless it’s after a cold front when the cooler air recreates a convective atmosphere and therefore showers form readily). You also need the showers to be on the same side as the sun – they can be in front of you as well, but you’ll need a shower, and the sun behind you.
You can spot them at any time of the year.
We don’t see a full circle because the earth gets in the way. The lower the sun is to the horizon, the more of the circle we see -right at sunset, we would see a full semicircle of the rainbow. The higher the sun is in the sky, the smaller is the arch of the rainbow above the horizon. If you can get a bit of altitude (a few hundred feet) on a rainbow friendly day you could see the whole rainbow…which will be circular. It’s something I’ve still not seen, and if anyone has a photo I would go crazy for it!
For the most colourtastic ones you need the big hefty showers with large raindrops. Large drops (a few millimetres in diameter) will create the brightest colours and most defined bands of colour.
No two people see the same rainbow. This is because a rainbow is produced with reference to one definite point – the eye of the observer – so each of us sees a slightly different rainbow. (In fact technically each eye sees a different one too!)
Also Ian Atkin messaged to ask if anyone has ever noticed that when there are 2 rainbows together the colours are reversed in the secondary one. He gives this explanation; “Given the correct conditions the principle of secondary total internal reflection can occur resulting a sister to your primary rainbow being created, however the spectral sequence is reversed due to the internal reflection and refraction across the wavelengths as the light rotates and exits the raindrop thereby swapping the colour sequence to now be Vi Bgyor and not Roy Gbiv (as we were all brought up to remember)” Thanks Ian!
Happy spotting! Oh, and one more thing; There probably isn’t a pot of gold at the end…but I’ll keep looking.