A Change in Angular Size of the Compact Source in the Crab Nebula

Observations of interplanetary scintillation at 81·5 MHz indicate that the angular diameter of the compact source in the Crab Nebula has increased from $${0}^{\prime{}\prime}\cdot2\,\text{to}\,{0}^{\prime{}\prime}\cdot7$$ over the period 1971–75. It is suggested that there has been an enhancement of scattering in a region close to the source.