Radio emission from the Sun was first reported in the scientific literature by Grote Reber in 1944. Those were observations of 160 MHz frequency (2 meters wavelength) microwave emission emanating from the chromosphere. However, the earliest known observation was in 1942 during World War II by British radar operators who detected an intense low-frequency solar radio burst; that information was kept secret as potentially useful in evading enemy radar, but was later described in a scientific journal after the war. One of the most significant discoveries from early solar radio astronomers such as Joseph Pawsey was that the Sun produces much more radio emission than expected from standard black body radiation. The explanation for this was proposed by Vitaly Ginzburg in 1946, who suggested that thermal bremsstrahlung emission from a million-degree corona was responsible. The existence of such extraordinarily high temperatures in the corona had previously been indicated by optical spectroscopy observations, but the idea remained controversial until it was later confirmed by the radio data.