It's #Imbolc / #Imbolg eve! Or was it #Oimelc? Hard to say honestly.
This is the Dawn Festival of Irish culture, paralleling similar festivals throughout "Spring". Officially it's Feb 1st, but things begin at Nightfall in Celtic culture, so it begins tonight.
Like Samhain, it's likely the festival was originally on a different Solar-Calendar date (e.g. "Old Samhain"), or instead that it was, like Christian Easter, falling on a Lunar event following a yearly Solar milestone.