The Multiple Mirror Telescope (MMT)
The 6.5 metre Multiple Mirror Telescope (MMT) is operated by the MMT Observatory (MMTO), a joint venture of the Smithsonian Institution and the University of Arizona. The MMT is located on the summit of Mt. Hopkins, the second highest peak in the Santa Rita Range, approximately 55 kilometres (30 miles) south of Tucson, Arizona.
Although called the Multiple Mirror Telescope, the name is now historical. Before 1999, the telescope consisted of six small mirrors which collected the light and focused it towards the telescopes instruments. After 1999, those mirrors were replaced with a single 6.5 m diameter mirror, collecting twice as much light as before. Despite the change in mirror, the old MMT name stuck.
 MMT |
Some facts about the telescope:
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Observatory site
This primary mirror was successfully installed on 25 March 1999, with testing
of systems and instruments taking place in late 1999.
Stages in production of the main mirror
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This image (right) shows the mould into which glass chunks are placed. These are used
to produce the mirror blank.
The blank is simply a solid piece of glass having the correct diameter and thickness. |
 The mould used to cast the mirror © MMT |
 Glass chippings placed in secondary mirror mould © MMT |
The mould for the mirror was then loaded with 10,000 kg of glass chunks. Here
we show an example of the process with a smaller 1 metre mirror being made.
Everything is placed in the furness and heated up until the glass melts. |
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After heat treatment the mirror blank is allowed to cool over a long
period of time.
The new blank is marked with tape at 60-degree intervals. |
 Once heated the mirror is allowed to set © MMT |
 The secondary mirror being ground into the right shape © MMT |
The next stage in the process is to grind the surface of the mirror
blank.
This is a long process (many days) that is only completed once the shape of the mirror is a perfect curve. The main light gathering mirror in all astronomical telescopes is curved in this way. This is because that mirror must bring all the light to a point or focus. At this point, a camera is positioned to take a pictures of the star or galaxy under investigation by the telescope. |
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Finally the mirror is given a reflective coating. This results in
about 99% of all the light falling onto the mirror being reflected.
The reflective coating is replaced every year or two because contaminants in the atmosphere attack the surface and reduce the reflectivity over time. |
 The finished secondary mirror © MMT |
