National Astronomical Observatory of Japan

TMT (Thirty Meter Telescope)

What is TMT?

TMT (Thirty Meter Telescope) is a next generation optical-infrared extremely large telescope with an aperture of 30 meters currently under development. Construction is proceeding through international collaboration between Japan, the United States, Canada, China, and India. Japan has the important responsibility of producing the main body structure of the telescope and producing the mirror segments for the primary mirror which gathers light. Once constructed, TMT will achieve unprecedented resolution and sensitivity.

The most outstanding feature of TMT is its huge primary mirror. As its name suggests, TMT’s primary mirror has a diameter of 30 meters. It is segmented mirror formed by combining 492 small hexagonal mirrors. In order to make full use of the primary mirror’s collecting power, TMT employs leading edge technology such as adaptive optics which correct for atmospheric fluctuations in real time. Development is proceeding for first-light instruments, such as the Infrared Imaging Spectrograph (IRIS), Wide-field Optical Spectrometer (WFOS), and Infra-Red Multi-object Spectrograph (IRMS), all of which will begin operation as soon as TMT is completed.



A new world of optical-infrared astronomy will be opened when TMT is completed. TMT is expected to revolutionize many research themes that have been started by the Subaru Telescope and other telescopes; for example the search for the furthest galaxies and the first stars in the early Universe; efficient spectroscopic observation of many galaxies and stars; and direct imaging and spectroscopic observation of extrasolar planets.


Aperture of primary mirror30 meters (492 segments)
FocusNasmyth focus
Combined focal length450 meters
Field of view15 arcminutes
Primary mirror F-number1
Diffraction limit 8 arc milliseconds (1 micrometer in wavelength)
Observing wavelength0.31 to 28 micrometers
Main observing instrumentsInfrared Imaging Spectrograph (IRIS)
Wide-field Optical Spectrometer (WFOS)
Infra-Red Multi-object Spectrograph (IRMS)


April 2005ELT (Extremely Large Telescope) Project Office established
July 2009Maunakea, Hawai‘i Island chosen as site for TMT
April 2010ELT Project Office renamed as the TMT Project Office
2012TMT Project Office renamed as the TMT-Japan Project Office
May 2014Thirty Meter Telescope International Observatory (TIO) established