That was an amazing rainbow show over the Philly region Saturday, and it foreshadows a gorgeous week

A serendipitous combination of end-of-day rains and the reappearance of the sun just as it was about to set created a spectacular rainbow show throughout the region Saturday.

A rainbow appears as an arc in the sky, however, in reality it is part of a circle of light created by raindrops and the sun — think of the light at the rim of a flashlight.

At the risk of wonkiness, the National Weather Service explains the process this way: “Light enters a water droplet, slowing down and bending as it goes from air to denser water. The light reflects off the inside of the droplet, separating into its component wavelengths, or color.”

This can happen only near sunset or sunrise, when the sun is low in the sky.

Forget about the pot of gold, by the way. The rainbow is an optical phenomenon, but as optical phenomena go, they don’t get much better.

Nor does the weather forecast for the week. The sky show came in the wake of a front that cooled things off in a hurry. Temperatures Monday morning will drop to near 50, the National Weather Service says, a good 10 to 15 degrees below normal.

The days will be sunny, forecasters say, with highs warming into the 80s by Tuesday and nights remaining cool. It is worth noting that foliage experts say that sunny days and cool nights are ideal conditions for persuading the trees to produce vibrant fall leaf color.

On Saturday, the colors belonged to the sky.

Here are some of the images that appeared on social media.