More info from Wookieepedia.com:
Note that Life Day most likely was originally intended as a stand-in for the American holiday of Thanksgiving, as the Holiday Special was originally aired on November 17, the day after Thanksgiving that year.
However, over time the term “holiday special” has caused most fans to misinterpret Life Day as a stand-in for Christmas instead, leading to games like Star Wars Galaxies and Star Wars Battlefront: Renegade Squadron to place Life Day on December 25. This is partly because after the initial US airing in November, the Holiday Special aired in December in other countries, where Thanksgiving is not observed and Christmas is the closest equivalent.
The canonical date for the observance of Life Day has, nevertheless, been established in what sources there are as December 25, or the equivalent thereof in the Wookiee calendar. Whether this means that Life Day actually is intended to be understood as a solstice festival akin to Christmas as opposed to a harvest festival akin to Thanksgiving is unknown.
Neither concept seems to hold much relevance on Kashyyyk, which appears to have temperate weather throughout the year (including on the Life Day we see in the Holiday Special) and where agriculture seems to be little practiced.
In honor of Life Day, here’s some of our favorite photos of celeb fans hanging out with Chewie.
Chewbacca & actor Milo Ventimiglia at the Fanboy premiere.