MMT Observatory

The MMT Observatory is a joint facility of the Smithsonian Institution and the University of Arizona. Located on the summit of Mt. Hopkins, about 50 miles south of Tucson, MMTO hosts the 6.5-meter MMT telescope.

Located on the summit of Mt. Hopkins some 50 miles south of Tucson, the MMT Observatory (MMTO) is owned and operated in partnership between the Smithsonian Institute and the University of Arizona.

Mt. Hopkins, nearly 9,000 feet in elevation, is the second highest peak in the Santa Rita Mountain Range, and an ideal location for operating the observatory.

After astronomers from both the Smithsonian Astrophysical Observatory and the University of Arizona became interested in a “multiple mirror telescope” (MMT), the two institutions signed a Memorandum of Understanding, committing both to collaborate in building and operating the new MMTO. The memorandum was signed in 1971.

The MMTO was built as a collection of six 1.8-meter mirrors. At the time, it was the third largest telescope in the world. It was also the first telescope to be housed in a rotating building and to be supported on ball bearings rather than hydrostatic bearings.

After nineteen years of productive operations, progress in the production of large mirrors—pioneered at the UA’s Mirror Lab—and new instrument technologies drove the desire to upgrade the telescope to utilize a single 6.5-m mirror in place of the smaller six-mirror array. The conversion would more than double the light-gathering power of the telescope and increase the area of sky the telescope could observe at one time by a factor of more than 300. The original telescope was decommissioned in 1998. The telescope enclosure was modified, the optics support structure was replaced, and a single 6.5-m primary mirror was installed. The new telescope was simply renamed the “MMT,” which is no longer an acronym.

The large, primary mirror now seen on the MMT telescope was cast at the UA’s Mirror Lab. New methods developed by Roger Angel at the University of Arizona allowed the casting of 10 tons of glass blocks into a honeycomb structure in a rotating oven. It took seven years from start to finish.

In 2016, scientists used the MMT to discover the most metal-poor galaxy in the observable universe.