Climate and Seasons
The typical weather in a particular region over a period of years is called the region's climate.
Climate patterns may be marked by traditional divisions of a year based on distinctive weather conditions, what we call "seasons." For example, the continental United States is considered a "temperate region" in which there are four seasons -- spring, summer, autumn (fall), and winter. On the other hand, in tropical regions of the Earth, there are generally only two seasons -- a dry season and a rainy season. Seasons are shaped by the relative position of the Earth to the Sun.
The continental United States is part of what geographers call the northern hemisphere. A hemisphere is one half of the Earth; when referring to a southern and northern hemisphere, the Earth is divided by the equator, an imaginary line that encircles the planet at equal distances from the North and South poles.