Another fun rainbow science activity involves a glass of water, a box and a bright sunny day. (The boys and I have done a lot of experiments, which we later found in 365 Science Experiments. This is one of them! This is an affiliate link.)
When the sun is shining bright, fill a glass with water. Place it on a low table in the direct sunlight. Then look for the rainbow! If you can’t see it at all or not very well, change the height of your glass, possibly setting it on a box rather than a low table.
Questions to ask
Where is the rainbow in relation to the water? On the floor or the ceiling? Maybe its on the wall?
What happens throughout the day as the sun moves? Does the rainbow move? Does it change in appearance?
What colors can you see? What order are they in? Do the colors appear to change when they fall on different colors of paper?
The water acts as a prism, making the light separate into wavelengths, or individual colors! That is why we see rainbows when it’s raining and sunny!