A White Christmas is a Christmas with the presence of snow: either on Christmas Eve or on Christmas Day, depending on local tradition. This phenomenon is most common in the northern countries of the Northern Hemisphere. Because December is at the beginning of the Southern Hemisphere summer, White Christmases there are extremely rare, except in Antarctica (uninhabited), in the Southern Alps / Kā Tiritiri o te Moana of New Zealand's South Island, and in parts of the Andes in South America as well as the southern tip of the continent, in places like Ushuaia, Argentina. The opposite of a white Christmas, when there is no snow and thus the ground is bare, is traditionally known as a "green Christmas," from the color of bare grass.