Millions of people from around the world are heading to Uttar Pradesh in India to participate in the Mahakumbh Mela, the largest religious gathering of people on earth. This year, around 400 million people are expected to attend the 45-day spectacle, which is so large it can be seen from space. The BBC’s Anahita Sachdev lists three things that you need to know about the Mela. | BBC News India