There are two ways to celebrate:
One is to offer thanks and express gratitude to the Divine.
The second is to forget the sadness and look at the bright side, knowing that life is eternally changing.
Thus, any excuse to celebrate is a good excuse! Like the evergreen Christmas tree, whose leaves cannot be withered away by any storm or snow, let's not forget that life too is evergreen and filled with hope in the face of despair. Similarly, our spirit is eternal, despite personal or social grief.
The nature of spirit is celebration; which is the best way to come out of any kind of gloom...