Ostara is one of the Lesser Wiccan Sabbats and is celebrated on the Spring Equinox. The variance, as with all Solar festivals, is due to the differences between the actual astronomical event and our calendar, so be sure to check the calendar each year.
Keep your thoughts positive because your thoughts become your words. Keep your words positive because your words become your behaviors. Keep your behaviors positive because your behaviors become your habits. Keep your habits positive because your habits become your values. Keep your values positive because your values become your destiny.