Of course, I had to check this out on Wikipedia, which pointed out that the second rainbow has the colours in reverse order to the first one. I didn't notice this last night but now that I look at the photo again, I can see that! A rainbow appears when the sun shines into drops of water in the Earth's atmosphere. The second rainbow is caused by a double reflection of sunlight within the raindrops. It's all rather scientific, it's probably better if you read it for yourself, if you are so inclined: http://en.wikipedia.org/wiki/Rainbow
It was certainly one of the clearest rainbows I have ever seen and I could see where it ended at ground level. As you can see from this second photo, it seemed to end right on top of this house, or at least, in the park across the street from it.
I was tempted to rush down and look for the leprechaun and his pot of gold that is said to be found at the end of a rainbow, but as Wikipedia points out, this is merely an optical effect - as the viewer walks towards it, it will move farther away. Good thing I didn't go chasing after it!