Whether you believe in astrology or not, there may be a correlation between when you were born and mood/personality.
A group of Hungarian researchers looked at more than 400 subjects and found correlations between when they were born and their personality types.
According to the study, people born in summer are more likely than people born during winter to have a cyclothymic temperament, featuring extreme mood swings. And people born during spring and summer were more likely to be extremely, even excessively positive--a mood condition known as hyperthymic temperament.
How season of your birth affects mood is still unknown. But other studies have found evidence that seasons can affect levels of brain chemicals such as dopamine and serotonin, which influence mood.
This does not that if you were born during autumn, for example, you will definitely not be depressed. Rather, the study suggests that people born in the fall are less likely to have a depressive temperament, just as people born during the winter are less likely to have an irritable temperament.
"Birth Season Affects Your Mood In Later Life" (EurekAlert)