The coherence properties of sunlight were first studied by Verdet around 1869 and were later examined by other scientists. However, all the previous calculations assumed that the Earth is in the far zone of the Sun, an assumption that is incorrect. An investigation of why Verdet's result is nevertheless correct reveals a surprising property of radiation from incoherent sources.
© 2004 Optical Society of America
Girish S. Agarwal, Greg Gbur, and Emil Wolf, "Coherence properties of sunlight," Opt. Lett. 29, 459-461 (2004)