Trinity Sunday is the first Sunday after Pentecost. It doesn't have a fixed date because Easter doesn't and therefore nor does Ascension Day (40 days post Easter) and Pentecost (50 days post Easter).
I've been told Trinity Sunday, inspires a sense of trepidation in preachers in some Anglican churches who observe the day. That's unfortunate, for Anglicans at least, because the Anglican tradition places the teaching of the Trinity liturgically1
at the centre of its worship.
