This is the Da Vinci Days poster for step 2
Why is the sky blue?
"The light that travels from the Sun to the Earth contains every color there is.  But the Earth's air lets the blue light shine through the best.  Sometimes when the air is very wet after it rains, it makes a rainbow with all the colors.  At sunset, red light can shine through as well."
Parade, 30 Jan 05
Where in the rainbow is the purple?
Light from the sun is white.  What direction is the light travelling when it appears blue?
What direction is it travelling when it appears reddish (like at sunrise or set)?
How many errors can you find in Parade's answer to "Why is the sky blue?"?
Da Vinci Days 2003