Unusual rainbow seen in St Augustine Florida April 6th 2011,.?

We were on holiday sunbathing round the pool, when I looked up there was this rainbow in a complete circle that looked like I was looking at the planet earth from above, with all the colours of the rainbow going round it. We told other people round the pool area and they were all amazed at this lovely sight, can you tell me the reason for this unusual formation. thank you Linda Thompson, Hull, Yorkshire.