How many satellites are orbiting Earth?

It seems like every week, another rocket is launched into space carrying rovers to Mars, tourists or, most commonly, satellites. The idea that “space is getting crowded” has been around for a few years now, but just how crowded is it? And how crowded is it going to get? I am a professor of physics and director of the Center for Space Science and Technology at the University of Massachusetts, Lowell. Many satellites that were put into orbit have gone dead and burned up in the atmosphere, but thousands remain. More

(Source: Astronomy Magazine - Sep 23)