The National Solar Observatory (NSO) is a United States public research institute to advance the knowledge of the physics of the Sun. NSO studies the Sun both as an astronomical object and as the dominant external influence on Earth.NSO is headquartered in Boulder and operates facilities at two locations - at the 4-meter Daniel K. Inouye Solar Telescope in the Haleakala Observatory on the island of Maui, and at Sacramento Peak near Sunspot in New Mexico.