People across the globe wake up happy and become progressively more grumpy throughout the day, a new study monitoring people's updates on Twitter throughout the day has revealed.
The survey analysed around 510 million posts on the social networking site over a two-year period.
Researchers used a computer programme that picked out key words indicating positive (happy and enthusiastic) and negative (sad and anxious) moods of 2.4 million users, then pitched these against the clock to work out when people appeared happiest.
The results indicated that people generally wake up feeling happy and full of optimism, then get gradually more and more desolate throughout the course of the day - only recovering at around 6.30pm, when the stresses of the work day are over. Mood levels were found to be lowest at around mid-morning and - perhaps unsurprisingly - peaked at weekends.
The findings, published in the journal Science, presented similar patterns in 84 countries across the world, despite varying geographical and cultural variables.
"PA (positive attitude) had two peaks; relatively early in the morning and again near midnight," wrote the researchers, led by sociology professor Michael Macy of New York's Cornell University.
"Although the shape of the rhythm was consistent across days, PA levels were generally higher on Saturday and Sunday than at any time during the weekdays, which points to possible effects of work-related stress, less sleep, and earlier wake time.
"PA decreased mid-morning (at the start of the work day) and increased in the evening (at the end of the work day)."
The study also appeared to indicate the presence of winter blues, with tweets becoming more positive as days lengthened into spring in various different countries, and less positive as they shortened into winter.