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Anisotropy is a term for directional-dependence of a property of something as opposed to isotropy which refers to the fact that a property is identical in all directions. In cosmology, the term is used to describe the uneven frequency (interpreted as uneven black-body temperature) of the cosmic microwave background (CMB anisotropies). The Wilkinson Microwave Anisotropy Probe (WMAP) and Planck missions mapped this. The uneven temperature is hypothesized to result from density variations in the universe from the era when the CMB was produced, and the angular scale and degree of the variations are studied to learn about the early universe. Surveys covering large distances and large parts of the sky are analyzed for parallel anisotropies regarding frequency of galaxy clusters, etc.
Another phenomenon in which the terms are used is in describing explosions such as supernovae, regarding whether it ejects energy equally in all possible directions (isotropic) or varying (anisotropic). Core collapse supernovae are thought to be often or always anisotropic (anisotropic explosion, also termed an asymmetric explosion), e.g., showing a more violent explosion in some particular direction. A theory is that they cause gamma-ray bursts in a particular direction, a notion supported by the observed nature of GRB afterglows.