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, Indigo , Blue, Green, Yellow, Orange and Red
that are blended together into white by our eye (the first person to demonstrate this was Newton). Since Newton's time we have come to realize that the EM spectrum includes a variety of wavelengths and frequencies that extend well beyond visible light and range from the longest radio waves to extremely short gamma rays. 

B. The EM spectrum 
Shorter Wavelength----->                  Increasing Frequency--->            Increasing Energy------->
Radio Microwave 
Infrared Visible ROYGBIV Ultraviolet X rays Gamma rays 
<-----Longer Wavelength               <--------Decreasing Frequency     <--------Decreasing Energy
As different as they might appear to us, these waves are all related, they are all EM waves, differing only in wavelength, frequency and energy. In space, they all travel at the CONSTANT speed of light, 300,000 km/s or 186,000 mi/s.