From an old 1966 slide. Going back to the "heroic" era of Shackleton, Mawson and Scott, Antarctic expeditions have always celebrated Midwinter on 21 June. This is probably the world's most international holiday, celebrated equally by Australians, Japanese, Russians, Americans, French, Poles, and all the many other nationalities with Antarctic stations: whatever their nation's politics and whatever their religion. In the "old" days before satellite communications, there often were "radio blackouts" for some time..... This was the only time all year when everyone went "formal".