In AOM theory, the same yin and yang forces of nature that are seen in the four seasons, influence the body. Yin is attributed to night time, cold temperature and contracting energy so therefore yin time of year is when there are long nights and short days, as in Autumn and Winter. Yang is the opposite, being daytime, hot temperature and expanding energy that we experience in Spring and Summer. Good health is when the body is in perfect balance, however illness and disease occurs when there is too much or not enough heat, cold, dryness, moisture and circulation.