Gemini Observatory’s new
imaging spectrograph, without the help of adaptive
optics, recently captured images that are among the
sharpest ever obtained of astronomical objects from
the ground.

Among the images and spectra acquired during recent
commissioning of the Gemini Multi-Object
Spectrograph (GMOS) on the 8-meter Gemini South
Telescope, one image is particularly compelling.
This Gemini image reveals remarkable details,
previously only seen from space, of the Hickson
Compact Group 87 (HCG87). HCG87 is a diverse group
of galaxies located about 400 million light years
away in the direction of the constellation
Capricornus. A striking comparison with the Hubble
Space Telescope Heritage image of this object,
including resolution data, can be viewed at

“Historically, the main advantage of large ground-
based telescopes, like Gemini, is their ability to
collect significantly more light for spectroscopy
than is possible with a telescope in space,” said
Phil Puxley, Associate Director of the Gemini South
Telescope. He explains, “The Hubble Space
Telescope is able to do things that are impossible
from the ground. However, ground-based telescopes
like Gemini, when conditions are right, approach
the quality of optical images now only possible
from space. One key area – spectroscopy of faint
objects, which requires large apertures and fine
image quality – is where large telescopes like
Gemini provide a powerful, complementary capability
to space-based telescopes.”

GMOS-South is currently undergoing commissioning on
the 8-meter Gemini South Telescope at Cerro Pachon,
Chile. “GMOS-South worked right out of the box, or
rather, right out of the 24 crates that brought the
2-ton instrument to Chile from Canada and the UK _
just like its northern counterpart did when it
arrived on Hawaii’s Mauna Kea,” says Dr. Bryan
Miller, head of the commissioning team. “The GMOS
program demonstrates the advantage of building two
nearly identical instruments. Experience and
software from GMOS-North have helped us commission
this instrument more rapidly and smoothly than we
could have done otherwise,” explains Dr. Miller.
He adds, “Although the images from GMOS-South are
spectacular, the instrument is primarily a
spectrograph and that is where its capabilities are
most significant for scientists.” GMOS-South is
expected to begin taking science data in August

As a multi-object spectrograph, GMOS is capable of
obtaining hundreds of spectra in one “snapshot.”
The ability to deliver high-resolution images is a
secondary function. “It used to take an entire
night to obtain one spectrum,” explains Dr. Inger
Jorgensen, who led the commissioning of the first
GMOS instrument on the Frederick C. Gillett Gemini
Telescope (Gemini North) over a year ago. “With
GMOS, we can collect 50-100 spectra simultaneously.
Combined with Gemini’s 8-meter mirror, we are now
able to efficiently study galaxies and galaxy
clusters at vast distances – distances so large
that the light has traveled for half the age of the
Universe or more before reaching Earth. This
capability presents unprecedented possibilities for
investigating how galaxies formed and evolved in
the early Universe.”

GMOS achieves this remarkable sensitivity partly
because of its technologically advanced detector,
which consists of over 28 million pixels, and
partly because of multiple innovative features of
the Gemini dome and telescope that reduce local
atmospheric distortions around the telescope.
“When we designed Gemini, we paid careful attention
to controlling heat sources and providing excellent
ventilation,” said Larry Stepp, former Gemini
Optics Manager. Stepp elaborates, “For example,
we constructed 3-story-high vents on the sides of
the Gemini enclosures. It is great to see this
image that provides such a dramatic validation of
our approach.”

“The twin Gemini Telescopes offer a unique
advantage,” explains Director of the Gemini
Observatory Dr. Matt Mountain. “Now that both
telescopes are equipped with nearly identical GMOS
instruments, we have created an unprecedented
uniform platform to coherently study and take deep
spectra of any object in the northern or southern
sky at optical wavelengths.”

Upgrades to GMOS-South that will increase its
variety of capabilities are planned even as the
instrument is undergoing commissioning. An
Integral Field Unit (IFU) on GMOS-South is
anticipated to begin commissioning in early 2004.
Jeremy Allington-Smith, leader of the IFU team at
the University of Durham said, “GMOS-South will
soon be fitted with an integral field unit like its
sister on Gemini North. Made by the University of
Durham, it uses more than a thousand optical
fibers, tipped at each end with microscopic lenses,
to dissect the object under study. This gives GMOS
a 3-D view of the target, in which each pixel in
the image is replaced by a spectrum. This
innovation allows GMOS to make detailed maps of,
for example, the motion of stars and gas in

GMOS was built as a joint partnership between
Gemini, Canada and the UK. Separately, the U.S.
National Optical Astronomy Observatory provided the
highly capable detector subsystem and related
software It is
anticipated that GMOS-South will be available for
full scientific operations in August 2003 when
astronomers from the seven-country Gemini
partnership will begin using the instrument for a
wide variety of scientific studies.

For a web version of this text, visit To obtain additional information,
visit Gemini’s homepage at http: A
gallery of images is available at

The Gemini Observatory is an international
collaboration that has built two identical 8-meter
telescopes. The Frederick C. Gillett Gemini
Telescope is located at Mauna Kea, Hawaii (Gemini
North) and the other telescope at Cerro Pach=F3n in
central Chile (Gemini South), and hence provide
full coverage of both hemispheres of the sky. Both
telescopes incorporate new technologies that allow
large, relatively thin mirrors under active control
to collect and focus both optical and infrared
radiation from space.

The Gemini Observatory provides the astronomical
communities in each partner country with state-of-
the-art astronomical facilities that allocate
observing time in proportion to each country’s
contribution. In addition to financial support,
each country also contributes significant
scientific and technical resources. The national
research agencies that form the Gemini partnership
include: the US National Science Foundation (NSF),
the UK Particle Physics and Astronomy Research
Council (PPARC), the Canadian National Research
Council (NRC), the Chilean Comision Nacional de
Investigacion Cientifica y Tecnologica (CONICYT),
the Australian Research Council (ARC), the
Argentinean Consejo Nacional de Investigaciones
Cientificas y Tecnicas (CONICET) and the Brazilian
Conselho Nacional de Desenvolvimento Cientifico e
Tecnologico (CNPq). The Observatory is managed by
the Association of Universities for Research in
Astronomy, Inc. (AURA) under a cooperative
agreement with the NSF. The NSF also serves as the
executive agency for the international partnership.