Why is a rainbow always an arc?

What you’ll see

Sunlight enters a raindrop, bends, bounces off the back and comes out again, spread into colours. Red leaves at forty two degrees from the sunlight, violet at forty. So only the drops sitting on a forty two degree circle around your shadow send red into your eye. That circle is the rainbow.

• Paper orbits look
• Narrated
• 20 seconds
• Laptop and phone versions