2015-07-19 – Yesterday was typical rainbow weather in Chicago: intermittent thundershowers. The key word here is “intermittent.” Rainbows appear when sunlight is scattered by raindrops. You need both, and that doesn’t happen often—mostly during the summer in Chicago. Certainly not in the winter.
If you know where to look, you can see them fairly frequently. They do not happen midday. Or, rather, they happen but they are in the ground, so you don’t see them (usually). When the sun is lower in the sky, the rainbow is higher and visible. That’s why you see them in the late afternoon and early evening.
You’d see them in the morning, too, if you would get out of bed!
When conditions are right, go outside stand with your back to the sun and look for an open patch of sky. Rainbows are always opposite the sun. If you look above the rainbow, you will notice that the sky above the bow is generally darker than the sky below. And if you look carefully into the darker sky above, you usually will see a second rainbow. I’ve even seen a third sequence of colors, though it wasn’t a complete bow. Scientists say that there are even more rainbows that you can see in a lab, but not in the sky.
Now, I just told you that you can’t see a rainbow at midday because the place where it would appear is in the ground. But I have seen a midday rainbow. I saw it from an airplane. And it was a full circle, appearing on clouds below. In the center of the circle was the shadow of the airplane.
In winter, you don’t normally see rainbows because it isn’t raining. You can, however, see a similar phenomenon produced by ice crystals. This is called a glory and appears as a halo around the sun. I used to sit on the west side of my northbound commuter train, so I would occasionally see these in the western sky, usually in February, on my trip home from work.