Dual nature of light. Light has both wave and particle properties.
All light waves travel in vacuum with same velocity.
Red is about 600 nm, blue about 400 nm. Most of the light waves are not visible to the eye. Increasing order of l are gamma rays, X-rays, ultra violet, visible, infrared, microwaves and radio waves. Solar eclipses and lunar eclipses occur about once every 1.5 years somewhere on the surface of the Earth. Virtual images are formed when the eye focuses the light rays and an image are formed in the eye.