Double Rainbow

The Ring Nebula (M57) versus the Morning Glory geyser pool at Yellowstone National Park. How is that they look so similar? I can answer that.

• M57 was once a star like the Sun which exhausted its hydrogen fuel and puffed up into a red giant giving off winds; it is a planetary nebula. At the center an aging super hot star emits ultraviolet radiation exciting the nearby gas the most thus giving off the blue color. Towards the edge the gas is cooler and appears red. This is a real color image. View M57 with even a pair of large binoculars (3 inch) and it will look like a smoky ring, moving up to a larger telescope the colors and structure will become visible.
• The Morning Glory pool is a hot spring in Yellowstone National Park. It is an upwelling of water geothermally heated by the Earth's tectonic activity. The water at the center is blue because of the intrinsic color of water (it preferentially absorbs red light) and the depth at the center of the pool. At the edges of the pool bacteria in microbial mats grow (bacteria are absent in the center because of the lack of light and high temperatures). The color of the bacteria is determined by the amount of pigments in them particularly chlorophyll and carotenoids. This is a real color image (also see this even more vibrant picture of the Morning Glory Pool). Perhaps, life started in a hot bubbly pool like this on the primordial Earth. 

Wow, these phenomena are self similar in their optical, geometric, and thermal properties. I will leave it as an exercise to the reader as to answer why nature is so amazing.