How can we tell that some stars are relatively close to Earth in the sky?
A) The stars appear to move periodically back and forth against the background stars because of Earth's movement around the Sun.
B) The stars appear to be extremely bright and must therefore be very close to us.
C) The stars are occasionally occulted or eclipsed by the Moon; hence, they must be close.
D) The light from these stars shows only a very small redshift caused by the universal expansion of the universe, so they must be close.

Question

Quizplus · Accepted Answer

Stars appear to move periodically back and forth against the background stars because of the Earth's movement around the Sun. This is called parallax, and the apparent shift in position can be used to calculate the distance to the star. The closer the star, the larger the parallax shift.

How Can We Tell That Some Stars Are Relatively Close