Coudé Echelle Spectrometer

The ESO Coudé Echelle Spectrometer (CES) was an instrument installed at La Silla Observatory at the beginning of the 1980s. It was designed to observe and analyse objects in the sky, such as the chemical composition of stars, at a very high resolution.

The CES installed on the 3.6-metre building was originally designed to be fed either from the Coude focus of the ESO 3.6-metre telescope or from the Coude Auxiliary Telescope (CAT), located in a separate building. Almost all the observations have been conducted with the CAT Telescope via a light tunnel connecting the CAT and the 3.6-metre building. Fiber link tests and a few observations were later done, with both the CAT and the ESO 3.6-metre telescope.

Some of the main characteristics of CES were the high resolving power and the computer-controlled support, which was a new way to operate, and was partly unknown by some astronomers at the time. “The user's interface has been designed to be as friendly as possible to observers, above all to visiting astronomers who may not be totally familiar with a computer-controlled instrument and the ESO image-processing system,” said Daniel Enard, one of the principal designers of CES in his article in The Messenger Issue 26.

CES underwent several upgrades during the years. New components like a CCD detector, image slicers and cameras were added, and remote operations from ESO HQ were implemented. In addition, new targets like exoplanets were included in science cases until the beginning of the 2000s, when CES was decommissioned.


The authoritative technical specifications as offered for astronomical observations are available from the Science Operation page.

Location: La Silla Observatory
Telescope: ESO 3.6-metre telescope
Focus: Cassegrain
Type: Visible Spectrograph
Wavelength coverage: 360-1100 nm
Spatial resolution:
Spectral resolution:
First light: May 1981
Science goal:
Images taken with the instrument: Link
Images of the instrument: Link
Videos related to the instrument: Link