Why Hindus fast on New Moon and Full Moon

Since time immemorial, Hindus have believed that the fortnightly cycle of the moon exerts a great influence on the human anatomy, just as it affects the water bodies on earth in cycles of tides. During a full moon, a person may tend to become restless, irritable and ill-tempered, showing signs of behavior that hints of 'lunacy'— a term derived from the Latin word for moon, "luna." Hence, in Hindu practice, there are specific rituals for the new moon and full moon days.