The Doppler shift is the change in wavelength of radiation due to relative motion between the source and the observer along the line of sight. If the object is approaching the observer, then the wavelength gets compressed, and the shift is toward the blue end of the visible spectrum, and the shift is called blueshift. If the object is moving away from the observer, then the wavelength gets elongated, and the shift is toward the red end of the visible spectrum, and the shift is called redshift. By comparing a spectrum from the moving object with a spectrum from the same elements at rest, you can calculate the velocity of the object using the Doppler shift formula. Chapter 3 Review Questions 1.
Refraction is the bending of light rays upon passing from one transparent medium to another.
For example, light that passes from air through a glass lense and then back to air will be bent from its original direction in a very predictable way. Reflection is the bouncing of light off of a reflective surface, such as a mirror. Reflection simply changes the direction of the light. The direction change can be controlled in a very accurate way if the shape of the mirror is precisely known. Refractive telescopes gather light from a large area, direct that light through a precisely shaped lense, which focuses the light onto a smaller area which can be viewed by a person or detector.