Morgan Catha

On the night of March 9–10, 2024, a cloud of plasma ejected by the Sun raced away from the star. It had already passed a distance of five solar radii when a ground-based array of 352 antennas in California's Owens Valley caught a brief radio signal from it.

The solar corona, the Sun's outer atmosphere, stretches millions of kilometers, yet it's visible only during a total eclipse or with specialized instruments. Typically, we gauge the corona's density by how it scatters white light, but that method relies on simplifications that can skew the results.

Listening to the cosmos requires patience and a finely tuned ear. Astronomers chose the most sensitive low-frequency instrument for this: the OVRO–LWA antenna array — 352 dipole antennas scattered across two and a half kilometers of California desert.