A. Light and Electromagnetic waves
How do we know anything about this universe in which we live? After all, we have barely stepped off the earth. While we have visited the moon and been in physical contact with the surface of Mars and Venus, it is doubtful that we will ever physically explore beyond the solar system. All that we know of the universe we learned from waves and light. Stars and galaxies all emit light and other electromagnetic waves; in fact all objects emit waves. From these waves we can figure out much about the objects that emit them or reflect them.
A wave is a disturbance that travels through space and carries energy.
There are all sorts of waves. Some waves, mechanical waves, such
as sound, earthquakes, or ocean waves, disturb matter, . Others waves are
electrical and magnetic in nature, electromagnetic waves (EM waves).
Light belongs in the latter category. What we see as white light is actually
a family of waves, a spectrum of 7 different colors (Violet,