Researchers with Cornell University used Twitter to monitor the attitudes of nearly 2.5 million people in 84 countries.
They tracked words like "happy" over the course of a day and week.
It turns out that people are happiest around 7 or 8 a.m. weekdays and on weekends.
However, no matter what day it is, our mood generally dips in the mid-morning, and then rises again in the evening.
Scientists think that might have to do with our biological clocks.