The famous social media site has created a program to be able to tell when we are happy or sad. 

Facebook can analyze the sorts of words you use in your comments and then figure out how you are feeling on any given day. It can then find out what the overall feeling of a population is on a certain date.

For example, a sad day for all in the USA, according to Facebook, was the say when actor Heath ledger died and also the say Michael Jackson died. The words used again and again on those days were: tragic, sad, doubt.

The days when people seem to be happiest and use happy words are on the weekends and holidays. 

For right now this system is only set up in the USA, but Facebook plans to export the feeling rater to other countries. Who knows, one day we may be able find out what our international emotion is from day to day?