SN Refsdal is the first detected multiply-lensed supernova, visible within the field of the galaxy cluster MACS J1149+2223.

It was named after Norwegian astrophysicist Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the universe.

[1] The supernova reappeared at the predicted position between 14 November and 11 December 2015[6] (with the exact date being uncertain by approximately one month which is the interval between two consecutive Hubble observations),[7] in excellent agreement with the blind model predictions made before the reappearance was observed.

[8][9][10] The time delay between the original quadruplet observed in 2014 and the latest appearance of the supernova in 2015 was used to infer the value of the Hubble constant.

[11] Using measurements from SN Refsdal and galaxy cluster lens models, astronomers found that the Hubble constant has value H0 = 66.6+4.1−3.3 km s−1 Mpc−1.