What can Twitter tell us about the collective world psyche? Quite a lot, according to a new study.

Using Twitter to monitor the attitudes of 2.4 million people in 84 countries, Cornell University researchers found that people all over the world awaken in a good mood. As the day progresses, however, that mood evaporates.

Positive tweets were more common on Saturdays and Sundays, another sign that work affects mood, something few working people would doubt.

Tracking Twitter tweets over two-years, the researchers found our emotions are shaped by work, sleep and the number of hours of daylight. These factors influence the sorts of emotions that color our days: enthusiasm, pleasure, alertness, distress, fear and anger.

That work affects mood is not new or particularly surprising, but the ability to tap into a large and culturally diverse populations via social media is. Using Twitter in conjunction with language monitoring software, graduate student Scott Golder and Michael Macy, Cornell professor of sociology discovered that positive feelings tend to peak twice a day – fairly early in the morning and around midnight, suggesting that mood is being shaped by workday experiences. Positive tweets were more common on Saturdays and Sundays, another sign that work affects mood, something few working people would doubt.

The study offers a view into our cultural similarities in these daily rhythms. For example, positive tweets and late-morning mood peaks were more prominent on Fridays and Saturdays in the United Arab Emirates, where, according to the paper, the traditional work week is Sunday through Thursday.

So, are seasonal effects, like the winter depression seen in seasonal affective disorder, common to other cultures? Golder and Macy did not find a direct correlation between daylight and mood reflected in the tweets; but they did see positive mood diminishing in relation to relative daylight, such as the gradually decreasing length of days between the summer and winter solstices.

The paper is published in September 29th issue of the journal Science.