Twitter index: happy birthday Mandela, RIP Khanna

Twitter users around the world are wishing a happy birthday to Nelson Mandela and mourning the death of Rajesh Khanna.

Former South African president Nelson Mandela celebrates his 94th birthday Wednesday.

Microbloggers are also mourning Rajesh Khanna, the Indian actor, producer and politician, who died at his home in Mumbai on July 18 after a long battle with a series of health problems.

Also causing a buzz on Twitter are teenage popstars Justin Bieber and One Direction's Niall Horan, who excited fans by exchanging a series of tweets congratulating one another on recent performances.

The top 10 most talked about topics on Twitter on July 18 at 10:40 AM GMT are:

01. #FirstDayOfSchoolThoughts
02. #benceasikolmak
03. #KalbimeGidenYol
04. Justin and Niall
05. RIP Rajesh Khanna
06. Happy Birthday Nelson Mandela
07. T.O.P & BNI Taplus Muda
08. Kartalice Demek Desiktas Demek
09. Özledik Be Fenerbahcem
10. Sadri Baskan Kimse Yoksa Biz Variz