The Native Indians had no clocks but used the environment to measure time. Sunset and sunrise organized the parameters of the day. The cycles of nature, the cold and warm seasons, organized task related work especially agricultural life such as the planting seasons. Rituals and special ceremonies were also scheduled by nature. The summer solstice scheduled the Sun Dance ritual of the Kiowa tribe, the spring equinox scheduled the First Thunder ceremony of the Pawnee tribe and the Zuni tribe celebrated the Great Feast of the Winter Solstice. Seasons are marked by the the turning of the sun on the solstices. Winter Solstice on December 21 marks the onset of winter, it is the shortest day of the year in the Northern Hemisphere. After the Winter Solstice, each day becomes longer until the longest day of the year arrives around June 21st.