The MMT is a telescope in Arizona, USA. It is run by the SAO and the University of Arizona. The area offers some of the best conditions for astronomy in the USA. This is because it is high above sea level, there is not much light pollution, and the skies are usually clear.
The MMT has a primary mirror which is 6.5 metres wide. It also has secondary mirrors which can be changed to fit what the astronomer want to observe. One mirror lets the MMT collect light across a large area of the sky. This allows the astronomer to observe several objects at once. Another mirror provides adaptive optics. This reduces blurring and gives sharper images. This lets the astronomer look at objects which are very far away in more detail.
The telescope used to be called the Multiple Mirror Telescope. It is now just the MMT. The original telescope had 6 small mirrors. These worked together to collect light and focus it towards the instruments. After 1998, the 6 mirrors were replaced with one large mirror. The new MMT can collect twice as much light as before.