ASK TOM WHY: What causes double rainbows?

Dear Tom,


My grandson, Donovan, noticed double rainbows at about 5 pm on October 3 and we were wondering what causes this phenomenon.


RoseMary Jandes and Donovan, Downers Grove


Dear RoseMary and Donovan,


The beauty and awe-inspiring sight of double rainbows caught the attention of many readers that afternoon. The inner rainbow (the primary) is brighter and smaller. It forms when sunlight passes through raindrops and, after refraction and a single reflection within a raindrop, leaves the drop and returns to our eyes separated into the colors of the spectrum: red on top, followed by orange, yellow, green, blue, indigo and violet on the inside.


A wider, fainter rainbow (the secondary) forms outside the primary when some of the light is reflected twice within the raindrops before emerging, thereby reversing the sequence of colors.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s