What is Gemini?

The William Herschel Deep Field – most of the coloured dots in this picture are not stars but distant galaxies, with redshifts z = 5 or 6. The redshifts correspond to distances of about 10 billion light years, showing that galaxies had already formed when the Universe was quite young. The image is combination of optical and near-infrared images from the 4.2m William Herschel telescope in the Canary Islands, and mid-infrared images from the 3.5m Calar Alto telescope in Spain. Image credit: Dr Tom Shanks (Durham University), William Herschel Telescope/Isaac Newton Group and Calar Alto Observatory/Max-Planck-Institut fuer Astronomie The Gemini project consists of twin observatories, in the Northern and Southern Hemispheres, giving astronomers coverage of the entire sky from the North Pole to the South. Gemini North is on top of Mauna Kea, an extinct volcano in Hawaii, while Gemini South is high in the Chilean Andes. These sites were chosen because they are the best observing sites in the world – the skies are clear almost all year round, while the dry air means the telescopes can be used in the infrared as well as visible wavelengths.

Like most leading-edge astronomy projects, Gemini is an international collaboration between several countries; the USA, UK, Canada Chile, Australia, Argentina and Brazil. The UK is the second largest contributor, with almost a 25% share in Gemini, and UK astronomers will receive a proportionate share of observing time on the telescopes.

What will Gemini do?

Star formation

Stars form deep within dense molecular clouds. Newly formed stars are hidden from view by the surrounding gas and dust, but can be studied by using infrared and radio telescopes. Gemini's sensitivity in the infrared allows astronomers to peer into molecular clouds and study the processes that occur in star-formation regions. Infrared spectroscopy gives us an insight into the physical conditions in these regions, and the molecular chemistry that occurs in the gas.

Galaxy formation

The image above shows distant galaxies, as seen in a series of ten hour exposures by the William Herschel telescope in the Canary Islands, and the Calar Alto telescope in Spain. Gemini has 10 times the light gathering power of the Hubble Space Telescope, and 4 times the power of the William Herschel Telescope, allowing astronomers to study much fainter (and hence, more distant) galaxies. This gives us the opportunity to look further out into space, or further back into the history of the Universe, in order to try and discover how galaxies were originally formed.

Brown Dwarfs

Brown dwarfs are objects which, like stars, formed out of dense clumps of gas and dust inside molecular clouds. However, unlike stars, they are not massive enough for nuclear fusion to have started in their cores. They are very dim at visible wavelengths, but should be detectable by an infrared telescope.

Active and adaptive optics

Shortly after its first coating in December 1998, engineer John Filhaber inspects the reflective coating on the 8-meter Gemini North mirror on Mauna Kea. The first test coating had a total of about 1.5 aluminium cans worth of aluminium over the entire surface of the mirror. The mirror has since been coated with silver, using a special technique, to significantly enhance infrared performance. Photo Courtesy of Gemini Observatory Gemini's mirrors use a combination of active and adaptive optics to improve the quality of the images delivered by the telescopes. Active control of the shape of the primary and secondary mirrors corrects for errors in tracking, compensates for buffetting of the telescopes by the wind and provides some compensation for the blurring effects of the Earth's atmosphere. At the same time, the adaptive optics system adjusts the shape of the primary mirror up to 100 times a second, in order to compensate for the blurring caused by atmospheric turbulence.