What is the small round sfere found in the middle of a opel/vauxhall Vectra's dashboard, under windscreen?

I saw that all cars in general have something like that on their dashboard right underneath the windscreen. Could it be a sensor of some sort or what?|||On most vehicles, this is an optical sensor to activate the automatic headlights.|||As with the above answer this may be a sensor for the auto headlamps, the other thing it could be is a sunload sensor for the vehicles automatic climate control, basically measuring how bright the sun is for the climate control ECU|||its to turn on the head lights but also it sences motion in cars with a motion detecting car alarm