Why do astronomers think that there may be other advanced civilizations?

What technologies are astronomers using to look for life on other planets? Why?

What are the challenges of looking for Dyson spheres?

Astronomers have theorized that there could be three types of civilizations. What are they? How would they be recognized? Which one has been ruled out so far?

Do you think an advanced civilization may exist in the universe? Why or why not?

PLZ help :)

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.