Polarimeter with Instrumental and Sky COmpensation

PISCO, the Polarimeter with Instrumental and Sky COmpensation, was designed by K. Metz and built at the University Observatory Munich with technical and financial support from ESO between 1984 and 1986. The instrument was mounted on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile and the first results were obtained during a commissioning run in September 1986.

PISCO’s design was an update of the Serkowski polarimeter design and it was capable of high precision linear and circular imaging polarimetry of objects down to approximately 17th magnitude. PISCO’s main feature was the possibility to correct directly for the sky polarisation and partly also for the instrumental polarisation.

The light collected by PISCO was measured with photomultipliers which had a fairly high sensitivity (quantum efficiency) between 300 and 1100 nm. The ability to compensate for the sky made PISCO suitable for collecting data even under relatively poor photometric conditions.

PISCO was used to observe several BL Lacertae objects, late-type Mira variables or young stellar objects.

PISCO was decommissioned from the MPG/ESO 2.2-metre telescope in the late 1990s.


This table lists the global capabilities of the instrument. The authoritative technical specifications as offered for astronomical observations are available from the Science Operations page.

Location: Decommissioned
Telescope: MPG/ESO 2.2-metre telescope
Focus: Cassegrain
Type: Polarimeter
Wavelength coverage: 300–1100 nm
Spatial resolution: Seeing limited
Spectral resolution: Broad-band filters
First light: 15 September 1986
Science goal:

Polarimetry of objects with:

  • strong magnetic fields
  • synchrotron radiation
  • non-axisymmetric geometry
  • accretion disks
Images taken with the instrument: N/A
Images of the instrument: N/A
Press Releases with the instrument: N/A
  • ESO
  • University Observatory Munich