Sjur Refsdal (30 December 1935 – 29 January 2009) was 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 doctorate at the Institute of Theoretical Astrophysics, University of Oslo. Later that year he became professor in astrophysics at the Hamburg Observatory^[1] 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.^[2] 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 Supernova (SN).^[3] This method was applied for the first time in 2018,^[4] with the homonymous SN Refsdal. 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.

He was a member of the Norwegian Academy of Science and Emeritus at the Institute for theoretical Astrophysics at the University of Oslo.^[5] On 1 February 2005 he was awarded the King's Medal of Merit in gold.

The first detected multiply-lensed supernova was nicknamed "SN Refsdal" in his honor.^[6][7]