go beyond the limitations of our eyes, we build telescopes and detectors that help us expand our physical perceptions. Some of these are the familiar visible-light telescopes seen at mountain-top observatories; they allow us to see fainter objects with more detail than our eyes alone could see. We also use sophisticated radio antennas and receivers—radio telescopes. In fact, there are different telescopes for all of the types of light in the electromagnetic spectrum: radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma-rays. Each kind of light has a different amount of energy and interacts differently with matter. By looking at what happens to light when it is emitted or absorbed by various types of objects, or when the light emitter is moving through space, we can determine important physical properties of astronomical objects, such as temperature, density, and chemical composition.