Measuring the large-scale anisotropy in the microwave background radiation

Measurements of large-scale anisotropy in the 2.7 K microwave background radiation are reaching a sensitivity of Delta T/T = 0.0001 in the amplitudes of low-order spherical harmonics. At this level, interesting conditions and processes in the early universe can be studied. However, the measurements are difficult and very susceptible to systematic errors. The microwave instruments and techniques are discussed with the emphasis on the reduction and evaluation of spurious effects. The subtraction of foreground radiation, mainly from diffuse Galactic sources, is a major problem that already limits the accuracy of measurements near 1 cm wavelength. Current results for the dipole and quadrupole moments are compared and discussed.