Keck I and Keck II Telescopes

“ A great observatory like the Keck is one of those human achievements which, like the Large Hadron Collider, the Human Genome Project, William Shakespeare and Franz Schubert – render me tearful with pride at belonging to the species Homo sapiens.”
— Richard Dawkins

An altitude-azimuth design gives each 10-meter Keck telescope the optimal balance of mass and strength. Extensive computer analysis determined the greatest strength and stiffness for the least amount of steel- about 270 tons per telescope. This is critically important, and not only for economic reasons. A large telescope must remain resistant to the deforming forces of gravity as it tracks objects moving across the night sky.

Chilling the interior of the insulated dome during the day controls temperature variations that could induce deformation of the telescope’s steel and mirrors. This is a big task: The volume of each dome is more than 700,000 cubic feet. Giant air conditioners run constantly during the day, keeping the dome temperature at or below freezing.

Astronomers use the telescopes in shifts of one to five nights. Time allocation committees pre-approve all observing. Assistants operate the telescopes at the summit while astronomers gather data via remote observing from observatory headquarters in Waimea. The W. M. Keck Observatory was the first facility on Mauna Kea to use remote observing.


A telescope tracks objects, sometimes for hours, across the sky as the Earth turns. This constant but subtle movement results in slight deformations of the telescope structure despite all engineered precautions. Without active, computer-controlled correction of the primary mirror, scientific observations would be impossible.

For the Keck telescopes, new techniques for manufacturing, polishing and testing their mirror segments had to be invented, including “stressed mirror” polishing. Each segment’s surface is so smooth that if it were the width of Earth, imperfections would be only three feet high.

On the telescope, each segment’s figure is kept stable by a system of extremely rigid support structures and adjustable warping harnesses. During observing, a computer-controlled system of sensors and actuators adjusts the position of each segment – relative to its neighbors – to an accuracy of four nanometers, about the size of a few molecules, or about 1/25,000 the diameter of a human hair. This twice-per-second adjustment effectively counters the tug of gravity.

Ever since their invention nearly 400 years ago, Earth-based telescopes have suffered from image blurring caused by the turbulent atmosphere above them. This is true of even the world’s best observatory sites like Mauna Kea, though to a considerably lesser extent than elsewhere. In recent years, advances in optical and computing technology have made it possible to greatly reduce this blurring through the use of “adaptive optics” (AO). At the heart of the AO system is a six-inch-wide deformable mirror that changes its shape up to 2,000 times per second to cancel out atmospheric distortion; the resulting images are therefore ten times sharper than previous images taken with the telescopes. Successfully installing AO systems on both Keck telescopes has made it possible for Keck astronomers to study objects in far greater detail than ever before.


VISIBLE BAND (0.3-1.0 Micron)

DEIMOS – The Deep Extragalactic Imaging Multi-Object Spectrograph is the most advanced optical spectrograph in the world, capable of gathering spectra from 130 galaxies or more in a single exposure. In ‘Mega Mask’ mode, DEIMOS can take spectra of more than 1,200 objects at once, using a special narrow-band filter.

ESI – The Echellette Spectrograph and Imager captures high-resolution spectra of very faint galaxies and quasars ranging from the blue to the infrared in a single exposure. It is a multimode instrument that allows users to switch among three modes during a night. It has produced some of the best non-AO images at the Observatory.

HIRES – The largest and most mechanically complex of the Keck’s main instruments, the High Resolution Echelle Spectrometer breaks up incoming starlight into its component colors to measure the precise intensity of each of thousands of color channels. Its spectral capabilities have resulted in many breakthrough discoveries, such as the detection of planets outside our solar system and direct evidence for a model of the Big Bang theory.

KCWI – The Keck Cosmic Web Imager is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution, various fields of view and image resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope enables studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters and lensed galaxies.

LRIS – The Low Resolution Imaging Spectrograph is a faint-light instrument capable of taking spectra and images of the most distant known objects in the universe. The instrument is equipped with a red arm and a blue arm to explore stellar populations of distant galaxies, active galactic nuclei, galactic clusters, and quasars.

NEAR-INFRARED (1-5 Micron)

ADAPTIVE OPTICSAdaptive optics senses and compensates for the atmospheric distortions of incoming starlight up to 1,000 times per second. This results in an improvement in image quality on fairly bright astronomical targets by a factor 10 to 20.

LASER GUIDE STAR ADAPTIVE OPTICS – The Keck Laser Guide Star expands the range of available targets for study with both the Keck I and Keck II adaptive optics systems. They use sodium lasers to excite sodium atoms that naturally exist in the atmosphere 90 km (55 miles) above the Earth’s surface. The laser creates an “artificial star” that allows the Keck adaptive optics system to observe 70-80 percent of the targets in the sky, compared to the 1 percent accessible without the laser.

MOSFIRE – The Multi-Object Spectrograph for Infrared Exploration gathers thousands of spectra from objects spanning a variety of distances, environments and physical conditions. What makes this huge, vacuum-cryogenic instrument unique is its ability to select up to 46 individual objects in the field of view and then record the infrared spectrum of all 46 objects simultaneously. When a new field is selected, a robotic mechanism inside the vacuum chamber reconfigures the distribution of tiny slits in the focal plane in under six minutes. Eight years in the making with First Light in 2012, MOSFIRE’s early performance results range from the discovery of ultra-cool, nearby substellar mass objects, to the detection of oxygen in young galaxies only 2 billion years after the Big Bang.

NIRC-2/AO – The second generation Near Infrared Camera works with the Keck Adaptive Optics system to produce the highest-resolution ground-based images and spectroscopy in the 1-5 micron range. Typical programs include mapping surface features on solar system bodies, searching for planets around other stars, and analyzing the morphology of remote galaxies.

NIRSPEC – The Near Infrared Spectrometer studies very high redshift radio galaxies, the motions and types of stars located near the Galactic Center, the nature of brown dwarfs, the nuclear regions of dusty starburst galaxies, active galactic nuclei, interstellar chemistry, stellar physics, and solar-system science.

OSIRIS – The OH-Suppressing Infrared Imaging Spectrograph is a near-infrared spectrograph for use with the Keck I adaptive optics system. OSIRIS takes spectra in a small field of view to provide a series of images at different wavelengths. The instrument allows astronomers to ignore wavelengths where the Earth’s atmosphere shines brightly due to emission from OH (hydroxl) molecules, thus allowing the detection of objects 10 times fainter than previously available.

Future Instrumentation

KCRM – he Keck Cosmic Reionization Mapper will complete the Keck Cosmic Web Imager (KCWI), the world’s most capable spectroscopic imager. The design for KCWI includes two separate channels to detect light in the blue and the red portions of the visible wavelength spectrum. KCWI-Blue was commissioned and started routine science observations in September 2017. The red channel of KCWI is KCRM; a powerful addition that will open a window for new discoveries at high redshifts.

KPF – The Keck Planet Finder (KPF) will be the most advanced spectrometer of its kind in the world. The instrument is a fiber-fed high-resolution, two-channel cross-dispersed echelle spectrometer for the visible wavelengths and is designed for the Keck II telescope. KPF allows precise measurements of the mass-density relationship in Earth-like exoplanets, which will help astronomers identify planets around other stars that are capable of supporting life.