Building the Giant Segmented Mirror Telescopes

The size and complexity of telescopes have grown enormously since Galileo first turned his simple 2-centimeter-diameter “spyglass” telescope to the heavens in 1609. The largest telescopes today are 10 meters in diameter, and much larger ones are being planned. Galileo made and used his telescope by himself. Today’s modern telescopes require hundreds of engineers and construction workers to design and build, and teams of astronomers and technicians to operate them. They cost many hundreds of millions of dollars, and once in place are difficult and expensive to move. Obtaining sufficient funds is always a challenge, and prime observing locations are not always easily obtained. Consequently, a lot of thought and effort goes into designing and locating a new telescope.

The next decade will see the completion of two new world-class astronomical observatories: the Atacama Large Millimeter/submillimeter Array (ALMA)—a coordinated array of up to 80 12-m antennas about 18 kilometers across on a plain in Northern Chile—and the James Webb Space Telescope—a 6.5-m mirror to be launched in 2013 to replace the amazingly successful Hubble Space Telescope. Complementing these two facilities, there are currently three projects underway to build the next world’s-largest optical-infrared telescope. All three projects are supported by the GSMT Program Office at the National Optical Astronomy Observatory.

In support of the design and development phase of Building the Giant Segmented Mirror Telescopes, the Educational Outreach group at the National Optical Astronomy Observatory in Tucson, AZ, has developed an educational module, Astronomical Site Selection, to introduce some engineering aspects of telescope design and development.

To begin the module, click on the Astronomical Site Selection link. For more information about the design and suggested classroom use of the module, follow the Teacher Information link.


The Giant Magellan Telescope (GMT) Project, a 24.5-m telescope.


The Thirty Meter Telescope (TMT) Project, a 30-m telescope.


The European Extremely Large Telescope (E-ELT) Project, a 30-60-meter telescope.