The magnetic field in the Sun's corona The solar corona is the outermost layer of the Sun's atmosphere, consisting of hot, diffuse, and highly ionized plasma. The magnetic field in this region is expected to drive many of its physical properties but has been difficult to measure with observations. Yang et al. used near-infrared imaging spectroscopy to determine the electron density and magnetohydrodynamic wave speed in the corona. By combining these measurements, they derived maps of the magnetic field throughout the entire observable corona. The method could potentially be used to produce routine magnetic field maps for the corona that are similar to those already available for the Sun's surface. Science , this issue p. 694