text: who decides when easter, fathers day n mothers day is? i know easter is something to do with the moon and the tides. easter falls on the first sunday after the first full moon after the vernal equinox (or autumnal equinox if you live in the southern hemisphere).  that's why it's called "a moveable feast."  it's a combination of catholic (sunday) and pagen (equinox, full moon) symbols.   father's day and mother's day are determined by whoever makes them up.  mother's day was created by a woman to honor her mother.  she lobbied various lawmakers until it became a quasi official holiday.  if you could get congress to establish a swedish one armed albinos day, you could pick the date....but it might be hard going to persuade anyone to honor this particular group.