Help with doppler effect?

Question

I need to:

understand the doppler effect with respect to light (red and blue shift) and sound

understand that astronomers use the doppler shift to estimate the distance of objects millions and billions of light-years away....

THANKYOU!

Answer 1

Light and sound have certain frequencies. As you travel towards the source the frequency will compress and be higher. As you travel away it will expand and become lower. That's why a train horn changes pitch as it speeds closer.

Answer 2

Imagine it like this.  You toss a ball at a wall and it bounces off.  It will bounce back toward you at the same speed that it hit the wall (simplified answer for this question).  Now imagine if that wall, like a baseball bat, swung toward the ball and hit it.  The ball would come back to you at a faster speed than you threw it .  That is because the forward momentum of the "wall" was added to the momentum of the ball.  If you know the original speed of the ball, you can subtract that from the speed you measure from the returning ball, giving you the speed of the moving wall.  The Doppler effect is this characteristic in frequency changes, as was described in the earlier answer.

Answer 3

Keep in mind that the astronomical Doppler shift is based on the expansion of space, with points farther from us expanding faster than those nearer to us.  So far, all the answers have give you the relative motion definition of the Doppler shift.  However, the spatial expansion explanation is the relevant one for astronomical distance measurements.  This Doppler shift is also relativistic, which is somewhat more complicated than non-relativistic Doppler.