Question

1. if we observe a doppler blue - shift from a star, the star must be a) relatively cool in temperature b) moving toward us c) a blue star d) moving away from us

Explanation:

The Doppler effect for light shows that a blue - shift occurs when the source of light (in this case, a star) is moving towards the observer. It is not related to the star's temperature or its actual color. Red - shift occurs when the star is moving away.

Answer:

B. moving toward us