List the major characteristics of the early 19c artistic movement known as the Hudson River School.

The Hudson River School was a mid-19th-century American art movement by a group of landscape painters, whose aesthetic vision was influenced by romanticism and luminism. Their paintings depict the Hudson River Valley and the surrounding area, as well as the Catskill Mountains, Adirondack Mountains, and White Mountains of New Hampshire. Note that "school" in this sense refers to a group of people whose outlook, inspiration, output, or style demonstrates a common thread, rather than a learning institution.