Weather is a set of all the phenomena occurring in a given atmosphere at a given time. WEather phenomena lie in the troposphere. WEather refers to current activity, as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of time. WHen used without qualification, "weather" is understood to be the weather of Earth. WEather occurs due to density (temperature and moisture) differences between one place and another. THese differences can occur due to the sun angle at any particular spot, which varies by latitude from the tropics.