I don't know what you guys think "raining fire in the sky" means but here's the true explanation:
In Denver's autobiography, he wrote: "I remember, almost to the moment, when that song started to take shape in my head. We were working on the next album and it was to be called Mother Nature's Son, after the the Beatles song, which I'd included. It was set for release in September. In mid August, Annie and I and some friends went up to Williams Lake to watch the first Perseid meteor showers. Imagine a moonless night in the Rockies in the dead of summer and you have it. I had insisted to everybody that it was going to be a glorious display. Spectacular, in fact.
The air was kind of hazy when we started out, but by ten p.m. it had grown clear. I had my guitar with me and a fishing rod. At some point, I went off in a raft to the middle of the lake, singing my heart out. It wasn't so much that I was singing to entertain anyone back on shore, but rather I was singing for the mountains and for the sky. Either my voice gave out or I got cold, but at any rate, I came in and found that everybody had kind of drifted off to their individual campsites to catnap. We were right below the tree line, just about ten thousand feet, and we hadn't seen too much activity in the sky yet. There was a stand of trees over by the lake, and about a dozen aspens scattered around. Around midnight, I had to get up to pee and stepped out into this open spot. It was dark over by those trees, darker than in the clearing. I looked over there and could see the shadow from the starlight. There was so much light from the stars in the sky that there was a noticeable difference between the clearing and everywhere else. The shadow of the starlight blew me away. Maybe it was the state I was in. I went back and lay down next to Annie in front of our tent, thinking everybody had gone to sleep, and thinking about how in nature all things, large and small, were interwoven, when swoosh, a meteor went smoking by. And from all over the campground came the awed responses "Do you see that?" It got bigger and bigger until the tail stretched out all the way across the sky and burned itself out. Everybody was awake, and it was raining fire in the sky.
I worked on the song - and the song worked on me - for a good couple of weeks. I was working one day with Mike Taylor, an acoustic guitarist who had performed with me at the Cellar Door and had moved out to Aspen. Mike sat down and showed me this guitar lick and suddenly the whole thing came together. It was just what the piece needed. When I realized what I had - another anthem, maybe; a true expression of one's self, maybe - we changed the sequencing of the album we'd just completed, and then we changed the album title."