The Sankt Andreasberg Observatory is located near the Rehberg on the premises of the Internationale Haus Sonnenberg, an international educational facility. It is one of the most elevated observatories in northern Germany. The air in an altitude of 710 metres is especially low on turbidity and since the Harz Nature Park is far away from big cities, there is far less light pollution there then in other parts of northern Germany. According to the Federal Agency for Nature Conservation, Sankt Andreasberg is one of the six best locations for astronomy in Germany. In April 2011 the Sky Quality Meter measured 21,81 mag/arcsec².