On this day, 61 years ago, on May 13, 1964 (April 2, 1964 in the lunar calendar), American astronomers Pang Seley and Wilson measured isotropic radiation in cosmic space. On May 13, 1964, American astronomers Pontselet and Wilson measured isotropic radiation in cosmic space at a wavelength of 7.35 centimeters. This phenomenon has since been observed in the radio band from 1 mm to 21 cm and in the X and gamma-ray bands. This phenomenon was later named cosmic background radiation and was one of the four major discoveries of astronomy in the 1960s. Cosmic background radiation is interpreted as residual radiation from the original fireball, with a corresponding redshift of approximately 3000. Peng Seley and Wilson also won the 1978 Nobel Prize in Physics.