I never thought about a rainbow being in a full circle until an airplane pilot told me that from the ground you can only see where it stops at the horizon.
Here is a photo of one from a site with more information:
earthsky.org/earth/can-you-ever-see-the-whole-circle-of-a-rainbow
Full circle rainbow was captured over Cottesloe Beach near Perth, Australia in 2013 by Colin Leonhardt of Birdseye View Photography. He was in a helicopter flying between a setting sun and a downpour. Used with permission
wordofthedaychallenge/rainbow/