A hemisphere is half of a sphere.
When Europeans arrived in the Western Hemisphere, they encountered diverse Indigenous cultures and civilizations, such as the Aztecs, Incas, and various North American tribes. These societies had established complex social structures, economies, and trade networks. The arrival of Europeans led to significant disruptions, including the spread of diseases, land dispossession, and violent conflicts, which drastically altered the demographics and cultures of the continent. Ultimately, this encounter marked the beginning of profound and often devastating changes for Indigenous peoples.
The first day of summer (on or about June 21 in the Northern Hermisphere) is the longest day of the year, meaning the most hours of sunlight. From there, each day is a little bit shorter until you come to the shortest day, the first day of winter (on or about December 21). Then they start getting longer again. The first day of summer is called the Summer Solstice, and the first day of winter is called the Winter Solstice.