Q:

You discuss calculating the distance and velocity of stars by measuring the "red shift" of their visible light as they move away from the Earth. It seems to me that you can only be sure that the light is "shifting red," instead of "really red" if you know the spectrum of a particular stars light prior to the shift.

I have two questions:

1. How do you know what a particular star's light would look like without the shift, so that you can calculate how much shift has occurred, and then the star's distance and velocity?

2. Do not visible portions of the electromagnetic spectrum, for example microwave and X-rays, also exhibit a "red shift" type of phenomenon? If so, what do you call and how do you measure this?

A:

1. Astronomers compare the spectrum from an arc lamp, other laboratory source, or some nearby star in which the spectral lines t are precisely known.

2. All forms of light experience spectral shifts depending on the their motion with respect to the observer. This shift is independent of the wavelength of the light.

Back | Index | Next