January 10, 2026

Longest observation of an active solar region

In May 2024, the strongest solar storm in twenty years lit up the skies—and stressed modern technology. An international team led by ETH Zurich has now produced the longest near-continuous observation of a single active solar region, tracking how it evolved over three solar rotations. The results help researchers better understand how extreme space weather builds up and how forecasts could be improved. From Earth, even the most dynamic regions on the Sun can usually be watched for only about two weeks before they rotate out of view. The ESA mission Solar Orbiter changes that perspective by observing the Sun from a different vantage point, including parts of the far side.

Between April and July 2024, Solar Orbiter monitored an exceptionally active region known as NOAA 13664—the same region linked to the intense geomagnetic storms in May 2024 and the spectacular auroras seen as far south as Switzerland.

A 94-day “movie” of a super-active region

To understand how such regions form and trigger eruptions, the researchers combined observations from two space probes: Solar Orbiter data from the far side and measurements from NASA’s Solar Dynamics Observatory, which observes the near side from the Earth–Sun line.

This made it possible to track NOAA 13664 almost continuously for 94 days—from its emergence on 16 April 2024 to its decay after 18 July 2024. Following one active region across three solar rotations is a milestone for solar physics and provides a unique dataset for studying how magnetic complexity grows over time.

Why it matters for space weather