These forces of nature greatly affect people’s moods (emotional conditions and feelings) too. For many people, winter in the northern regions is very depressing. They eat and sleep a lot, but they usually feel tired. They are nervous and can’t work well. They are irritable (not very nice to other people). Biometeorologists even have a name for this condition. The name is Seasonal Affective Disorder (SAD). Scientist think that the cause of this mood disorder is the long periods of darkness. Even during the day, it is often cloudy or gray. What can people with SAD do about of moods? Naturally, they need more light! On bright days they feel better. But people don’t work very well on sunny, hot, and humid days. The best weather for good work and thinking is cool and clear.