What do astronomers mean by light pollution?
A) Light pollution refers to pollution caused by light industry as opposed to heavy industry.
B) Light pollution refers to harmful gases emitted by common street lights.
C) Light pollution refers to light used for human activities that brightens the sky and hinders astronomical observations.
D) Light pollution refers to the lights that must be used inside major observatories and that make it difficult for astronomers' eyes to adapt to darkness.
E) Light pollution is another name for sunlight, which makes it impossible to see stars in the daytime.
Answer: C