Complex sentence: Despite this, Sweden did not accept the Gregorian rules for determining Easter until 1844; from 1753 until then, Sweden observed Easter on the Sunday after the first astronomical full moon after the true vernal equinox.
Split into simpler sentences: Despite this, Sweden did not immediately accept the Gregorian rules for determining Easter. From 1753 to 1844, Sweden observed Easter on the Sunday after the first astronomical full moon after the true vernal equinox.