RESUMO
High-resolution microwave observations are providing new insights into the nature of active regions and eruptions on the sun and nearby stars. The strength, evolution, and structure of magnetic fields in coronal loops can be determined by multiple-wavelength observations with the Very Large Array. Flare models can be tested with Very Large Array snapshot maps, which have angular resolutions of better than 1 second of arc in time periods as short as 10 seconds. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interactions of two or more loops. Magnetic reconnection at the interface of two closed loops may accelerate electrons and trigger the release of microwave energy in the coronal parts of the magnetic loops. Nearby main-sequence stars of late spectral type emit slowly varying microwave radiation and stellar microwave bursts that show striking similarities to those of the sun.