Twitter messages are short but can say a lot about the state of mind of English-speakers around the world.
After analyzing 4.6 billion tweets, researchers were able to follow levels of happiness.
It turns out the last months of each year, Saturdays, and the early mornings are happy times.
January, the first days of the week and late-nights are NOT.
Holidays and individual events, like a royal marriage or the death of a celebrity, can also have major effects on mood.
Daily happiness peaked at 5 a.m. to 6 a.m., then went down. It hit a low from 10 p.m. to 11 p.m., then peaked again overnight.
With holidays, happiness was highest on Christmas Day, followed by Christmas Eve.
There were sad days, too.
The bailout of the US financial system led to depression among twitterers.
Michael Jackson's death had the biggest single-day drop in mood.