As we cross the half-way point of the year, Twitter users are now sending 200 million Tweets per day.

In January 2009, users were sending 2 million Tweets a day, and this time last year the number was 65 million a day.

Here are the top Tending Topics for the first six months of 2011, split into the two most popular categories:

World News/Events

AH1N1 - Swine Flu
Mubarak - Former Egyptian President
Easter - Christian holiday
Cairo - Capital of Egypt
#prayforjapan – Relating to the March earthquake and tsunami
Chernobyl – Relating to the 25^th anniversary of the nuclear disaster in 1986
Libia/Libya – Relating to the ongoing civil war
Fukushima - Japanese nuclear power plant
William & Kate – ‘The Wedding’
Gadafi - Libyan political leader

Pop culture

Rebecca Black – Some annoying popular YouTube pop singer
Femme Fatale - Britney Spears’ latest album
Charlie Sheen - Actor
#tigerblood - Hashtag popularised by Charlie Sheen
Nate Dogg - Rapper
Anderson Silva - Brazilian UFC mixed martial artist
Tom & Jerry - Cartoon
Mumford & Sons - British band
Bieber alert – Relating to the nuisance that is Justin Bieber
Queen Gaga - Referring to pop artist Lady Gaga

Official source