Last updated:
February 14, 2001



Laboratório Nacional de Astrofísica

Pico dos Dias Observatory (OPD)



8.1-meter Telescopes. An International Project: USA, United Kingdom, Canada, Chile, Australia, Argentina, Brazil.

The Gemini Project

The Gemini Project is an international partnership to build two 8-meter telescopes, one on Mauna Kea, Hawaii, and one on Cerro Pachon, Chile. The telescopes and auxiliary instrumentation will be international facilities open to the scientific communities of the member countries. Siting the telescopes on Mauna Kea (elevation 13,822 ft.) in Hawaii and Cerro Pachon (elevation 8895 ft.) near Cerro Tololo in central Chile will provide complete sky coverage, making key astronomical objects (e.g. Magellanic Clouds, M31, M32 and M33) accessible regardless of location on the celestial sphere. Both sites offer high percentages of clear weather and excellent atmospheric stability.

The Gemini telescopes are designed to exploit the best image quality allowed by the Earth's atmosphere at these sites. Images approaching 0.1 arcsec in size will be achieved near 2.2´m, with near diffraction limited imaging at longer wavelengths. Optical images of  Gemini IR performance, especially on Mauna Kea, will be further enhanced by minimizing the telescope contributions to the thermal IR backgrounds. The combination of large aperture, excellent imaging, and low IR background give the Gemini Telescopes an order of magnitude sensitivity increase over existing 4-meter class telescopes for many applications.

Initial instruments will provide a basic set of capabilities for IR and optical imaging and spectroscopy. Instruments will be constructed as work packages to be managed by the national project offices in the partner countries.

Gemini Goals

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Image Quality:

The telescopes will achieve near diffraction-limited images at 2.2´m and beyond, with minimal degradation of the best seeing conditions at shorter wavelengths. The telescope optics are compatible with adaptive optics.

Infrared Optimization:

Utilization of the articulated secondary as pupil stop, together with protected silver on Mauna Kea mirrors, yields telescope IR emissivity of ~4% (requirement) or ~2% (goal). This is comparable to the minimum atmospheric emissivity in the thermal IR windows on Mauna Kea.

Multiple Instruments for Versatile Observing:

Instrument interface will co-mount 3 to 5 science instruments with masses of up to 2 tons and capabilities ranging from the UV to beyond 30 ´m. Instrument interface will also house acquisition and guiding, low order adaptive optics module, and calibration facilities.

Operations Philosophy:

Gemini will support remote, queue, and classical observer-on-site observing modes. Switches between instruments can be made in minutes. Data will be archived.

Gemini Image Quality

Superb Mirror Surfaces:

The Gemini primary mirror surfaces will be locally very smooth, with global figure controlled by active mirror support system.

Active Optics:

The optics alignment and primary mirror figure will be updated via on-board wavefront sensors every few minutes to correct for gravity and thermal deformation.

Fast Guiding:

A focal plane sensor within the science instrument isokinetic patch will control fast guiding at > 10 Hz via the tip-tilt secondary mirror. Fast guiding will remove the atmospheric component of seeing and compensate for telescope wind shake and wavefront tilt.

Advanced Mirror Support System:

A stiff mirror cell and 3-6 zone switchable hydraulic whiffle tree support system will allow the primary mirror to passively resist wind buffeting.

System Thermal Control:

The enclosure, telescope and optics are designed for active thermal matching to environment, in order to minimize self-induced seeing effects.

Control of Airflows:

The telescope primary mirror will be located 20 meters above the ground, which is well above the boundary layer. The enclosure ventilation will be controlled for optimum flushing and wind reduction.

Scientific Opportunities


How do stars form and what conditions lead to protostellar collapse? Young stars are shrouded by dust and can be seen primarily in the IR. The imaging performance of Gemini telescopes will permit study of protostellar objects, disks, jets, and protostars themselves, down to the scale of the diameter of Jupiter's orbit, in nearby star-forming regions.

Origins of Heavy Elements:

Stellar nuclear furnaces leave their distinctive signatures in isotopic abundance patterns of the metals which they synthesize. Spectroscopic studies of stars with varying ages and metallicities will reveal the history of heavy element production in our Milky Way galaxy, as well as its two nearest neighbors, the Magellanic Clouds. Complementary studies of the variety of abundance patterns in quasar absorbers will begin to reveal the dependence of enrichment on local environment.

Gravitational Lenses:

Einstein bows can be seen in clusters of galaxies, and rings or multiple images behind individual galaxies, all due to lensing effects of gravitating masses. Detailed studies require the Gemini combination of wavelength coverage, angular resolution and sensitivity to probe matter distributions and distinguish the signatures of microlensing and variable substructures within lensed sources.

Galaxies at High Redshift:

How did galaxies form and evolve in the Universe? Excellent images and superb IR performance will allow Gemini to reach the farthest known galaxies, explore their structures and stellar content, and provide the key to understanding the relation between stellar populations, chemical enrichment history, and the dynamical history of present day galaxies.