Why are there fewer and fewer stars in the sky?

Because of air pollution, light pollution and thermal convection.

Most of the stars in the sky are out of sight now. In fact, there are three fundamental reasons. The first is air pollution. Now with the development of industry and urbanization, the earth's atmosphere is full of dust on a large scale, which will block some starlight and some less bright stars.

The second is light pollution. In big cities, street lamps, neon lights on billboards, car headlights and lighting of various buildings are constantly flashing, and the released light is reflected in the air. Lasers are stronger than the twinkling stars at night, so it is difficult for us to see them. This truth is actually the same as not seeing the stars during the day, except that the lights are not as bright as the sunlight.

The third type is thermal convection, which is mainly caused by human use of fuel and electricity. Heating the air will increase the disturbance, and the direct starlight in the atmosphere will be disturbed, resulting in scattering and reduced visibility.