Rainbow..prism and more

White light is reflected from the droplets almost straight ahead.

The light in the lower portion is caused by diffraction. We have a similar problem in Newtonian telescopes.

Those bright cruciform spikes you often see in photos taken of stars are a good example of what happens when light is diffracted.

The cause of the spikes at pin point sources of light (like around stars) is the telescope spider that holds the secondary mirror.

Incoming light strikes those thin metal blades and forms that brilliant spike you see at each star. When that happens, light also scatters on either side of the spike causing a loss in contrast

Some of us get rid of those spikes by building obstruction free telescopes (Schiefspieglers)

Sometimes we use curved spiders in Newtonians instead of the straight ones.

The diffraction is still there with curved spiders, but the curved spider distributes the scattered light over the entire view and is thus not nearly as apparent.

The colored rainbow is also the result of light diffraction in the water droplets but it occurs to such a degree that it causes separation into segments of the visible spectrum.

The brighter area below the rainbow is also diffracted light but not quite to the degree needed to see it's component colors. And, like driving in fog, the loss of contrast is caused by the same scattered light that makes it appear brighter.

L. J.

It's obvious on the face of it: Your future's so bright, you oughta wear shades...

I was in a airplane a month ago and had the chance to see a completely circular rainbow. The sun was on the other side of the plane about 60 degrees up. The rainbow was visible on the surface of the clouds with the shadow of the airplane in the middle. The Stewart had never seen this.

This was different from the semi-circular version we see from earth.

Was I lucky?