Sensitive measurement of fluctuations in the cosmic microwave background

Extensive high sensitivity observations of the cosmic microwave background have been made on an angular scale of 8° covering a substantial fraction of the northern sky. An observed anisotropy in the sky emission at a level of δT/T = 3.7×l0^-5 has been detected (T is temperature). This level should strictly be interpreted as an upper limit to the cosmic microwave background fluctuations. It is possibly the direct imprint of density perturbations in the early Universe.