How can astronomers tell that some stars are relatively close to Earth?
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 Earth.
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

The phenomenon described in choice A is known as parallax, where the apparent position of a star shifts against the background of more distant stars due to Earth's orbit around the Sun. This effect is more pronounced for closer stars, allowing astronomers to measure their distances from Earth.

How Can Astronomers Tell That Some Stars Are Relatively Close