Rainbows are full circles, not semicircles – it’s just that from the ground you can usually only see their upper half. From the air, as this video from skydiver Anthony Killeen shows, the full circle can be seen in all its glory.
The Knowledge
You tube video added
Well, I’ll go to the foot of our stairs … 
Video? Judging by the other comments, I might not be the only person who can’t see the video. Without that, it’s hard to be persuaded.
Here’s a photo:
That rounds things off nicely! The thrilling moment a skydiver soars over a rare rainbow in the shape of a perfect circle
- British expat Anthony Killeen saw the 360-degree rainbow in New Zealand
- He was skydiving with an instructor when they spotted it mid-descent
- All rainbows are in fact circular, but can’t often be seen from the ground
Well you learn something new everyday.
I love seeing a rainbow,especially a double one.
Ah bless you Omah.
Thank you.
For the skeptics among us, this is the science of why we can only see half the rainbow.
Well, I never knew that!
But I’ve decided not to believe it in anyway because what about the pit of gold at the end of the rainbow and those poor leprachauns?
Of course they are circular, it is all geometry
That 42° is also the maximum angle the sun can be above the horizon (obviously that doesn’t apply to an airborne viewer.)
Now I’ll never forget that next time I see a rainbow
I’ve seen a full circle of rainbow around the sun three times. These occur when clouds were coming in to cover the sun. When the front arrives they can form around the sun.
Each time I’ve seen one it was followed by heavy snow
I have seen that too and also around the moon - I think the geometry of that is different because it is caused by ice crystals and I vaguely remember reading that the refractive index isn’t the same as raindrops.
Wonder if this means the pot of Gold is actually in the middle 
Wouldn’t that mean that in more cases, you’d be standing on it? 
Maybe that’s what it means, you are the pot of gold 
