Sjur Refsdal

Prof Sjur Refsdal (born December 30, 1935) is a Norwegian astrophysicist, born in Oslo. He is best known for his pioneer work on gravitational lensing, including the Chang-Refsdal lens.

In 1970 he earned a PhD at the Institute of Theoretical Astrophysics, University of Oslo.Later that year he became professor in astrophysics at the Hamburg Observatory in Germany, and remained in that position until he retired in 2001.

In 1964 and 1966 he published a series of articles on the effects and possible applications of gravitational lenses. He is particularly known for the "Refsdal Method", which describes how one may estimate the expansion rate of the Universe (Hubble constant) using the measured time-delay and lens properties of a gravitationally lensed quasar (QSO). He later started work on stellar evolution, but returned to gravitational lensing shortly before the first detection of a gravitational lens, dubbed the Twin Quasar.

On February 1 2005 he was awarded the Kings Medal of Merit in Gold ( in Norwegian).