Final answer:
Observatories must be in areas with dark skies and low water vapor to avoid light pollution and blurred star images caused by turbulence in the air.
Step-by-step explanation:
When the atmosphere is opaque, observatories must be located in areas with
dark skies and low water vapor, preferably away from large cities. This is because the atmosphere scatters the glare from lights near cities, causing light pollution that hides faint stars and limits the distances that can be observed by telescopes. Observatories are best positioned at least 100 miles away from the nearest large city to minimize light pollution. In addition, the air in the atmosphere is often unsteady, which leads to
blurred star images. This phenomenon, known as 'bad seeing,' is caused by turbulence in the air. Therefore, observatories are typically established in high-altitude locations with dry climates.