A lower frequency is measured for the spectral line emitted by the sun.
Work Step by Step
Strong gravitation expands time intervals, i.e., it slows down the passage of time. The gravitational field is about 28 times stronger at the sun's surface than it is on Earth's surface. Atoms at the sun's surface vibrate more slowly and emit light of a lower frequency than corresponding atoms on Earth. This is discussed on page 692.