NASA
National Aeronautics and Space Administration: Scijinks: Atmosphere
Activity describing how the Earth's atmosphere was formed, why it stays close to the Earth, and why the sky is blue.
Science Made Simple
Science Made Simple: Why Is the Sky Blue?
This website has three different projects from which to choose on the topic of why the sky is blue. Also, you can scroll up to learn more about why the sky is blue.
Physics Classroom
The Physics Classroom: Light Waves and Color: Blue Skies and Red Sunsets
Students will focus on the interaction of sunlight with atmospheric particles to produce blue skies and red sunsets.
Synopsys
Synopsys: A Gentle Intro to Optical Design: Why Is the Sky Blue?
Discusses Rayleigh scattering in plain language and attributes the blueness of the skies to this phenomenon. Discussion of scattering is just one topic of many on this lengthy page of optical topics.