A few things I have learnt about rainbows and when and where to look for them:
1. Rainbows in the sky seen from the ground are commonly opposite to the sun with the sun unobscured.
2. The more common ones occur in slight drizzles when the sun is near the horizon. Sometimes they occur in a halo around the sun, but those are seen when the sun is overhead.
3. Due to optics of water droplets, there are always two rainbows with spectrum colour sequences opposite to each other, but the second one (usually on top) is often much less obvious.
4. The order of colours in the spectrum of a rainbow is always the same, relative to each other.

Enjoy the next rainbow and see if the above are all true.

Photo © Richard W J Koh, in New Zealand 2011. www.amaranthine.photos

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