Harvest Moon Festival
From Nookipedia, the Animal Crossing wiki
The date of this event varies each year, as it occurs on the date of the full moon that occurs closest to the Autumnal Equinox.
In Animal Crossing
In Animal Crossing: City Folk
In Animal Crossing: City Folk, the Harvest Moon festival varies depending on the player's (or current host's) region. In the US and European versions of the game, it is referred to as the Autumn Moon, while in a Japanese regional game, the event is referred to as "Tsukimi" (Moon Viewing Festival). The celebration itself lasts from 6 a.m. until 12 a.m..
In New Leaf
In Animal Crossing: New Leaf, the event works similarly to City Folk, except Isabelle is now the host of the event. She awaits in the Plaza, giving a player a gift, depending on the player's region. In Korean versions, she gives them songpyeon. In European and American versions, she gives them a veggie basket and a wheat bundle, respectively. The standee is also different between regions. In Japanese versions, a table with dango on it is being overlooked by a mountain and a moon, where the player can make pictures from there. In the North American version, it's a scarecrow in a farm field where the player can pose for pictures overlooking the Autumn Moon.