Thus, T " varies between about 740 and 1350 K . During very quiet magnetospheric conditions, the still continuously flowing magnetospheric energy input contributes by about 250 K to the residual temperature of 500 K in eq . ( 2 ).
2.
In 1989 NASA launched the Cosmic Background Explorer satellite ( COBE ) which made two major advances : in 1990, high-precision spectrum measurements showed the CMB frequency spectrum is an almost perfect blackbody with no deviations at a level of 1 part in 10 4, and measured a residual temperature of 2.726 K ( more recent measurements have revised this figure down slightly to 2.7255 K ); then in 1992 further COBE measurements discovered tiny fluctuations ( anisotropies ) in the CMB temperature across the sky, at a level of about one part in 10 5.