Ripples in the cosmic microwave background. Coloured temperature map of part of the sky showing variations in the cosmic microwave background radiation (CMBR). The mean temperature of the CMBR is about 2.7 Kelvin (-270.4 Celsius.) The variations seen here are around 0.0001 degree (white is hotter, black is cooler). Each of these blobs covers an area of the sky similar to a full Moon. It is thought that these differences reveal the large-scale structure of the universe just 100,000 years after its creation in the Big Bang. The image was made using the Cosmic Anisotropy Telescope at Cambridge in 1996.