The night sky above the Aoraki National Park and Mackenzie Basin in Canterbury has been declared an International Dark Sky Reserve - one of only four in the world.
"To put it simply, it is one of the best star-gazing sites on Earth," executive director Bob Parks said.
More than 4300sq km of sky in the South Island is now protected as a reserve. That makes it the largest in the world.
The skies are almost completely free from light pollution.
Outdoor lighting controls were put into place in the area in the early 1980s, which helped to minimise light pollution around the Mt John Observatory, which overlooks the Tekapo township.