Final answer:
The wavelength of light increases when it moves away from a strong gravitational field, a phenomenon known as gravitational redshift. The light's frequency decreases due to the influence of gravity, but its speed remains constant.
Step-by-step explanation:
As light travels outward through the gravitational field of a planet or star and the field becomes less strong, the wavelength of the light increases. This phenomenon is known as gravitational redshift. When light leaves a strong gravitational field, it 'climbs out' of the gravitational well, losing energy in the process. The loss of energy due to gravity is evidenced by a decrease in frequency and a corresponding increase in wavelength, but the speed of light remains constant. This behavior reflects the fact that time runs more slowly in stronger gravitational fields, which means that seen from a distance, the light waves appear to stretch out and have a longer wavelength.