Telescope Upgrade Reveals Sun’s ‘Coronal Rain’ in Unprecedented Detail

The Sun’s outer atmosphere—the corona—is the piping hot outer limit of our star, and is usually hidden from view except during rare total eclipses. Now, scientists have gotten their clearest look ever at this mysterious region, thanks to a new adaptive optics system that scrubs away atmospheric blur, revealing fine views of the wispy plasma on the star’s surface.

Researchers from the National Solar Observatory and New Jersey Institute of Technology unveiled the system today, along with dazzling new images and videos of the Sun’s corona. The findings, published in Nature Astronomy, show fine-scale structures in solar prominences, short-lived plasma jets called spicules, and even coronal rain: cooling plasma that falls back to the solar surface along the star’s magnetic field lines.

The team’s imaging breakthrough hinges on a technology called coronal adaptive optics. Installed on the 5.25-foot (1.6-meter) Goode Solar Telescope in California, the new system—nicknamed “Cona”—adjusts a mirror 2,200 times per second to correct for distortions caused by the churn of Earth’s atmosphere. The remarkable technology counterbalances any would-be wobble in the telescope, thereby producing particularly sharp images of the corona.

“This technological advancement is a game-changer,” said Dirk Schmidt, an adaptive optics scientist at NSO and the study’s lead author, in an observatory release. “There is a lot to discover when you boost your resolution by a factor of 10.”

A solar prominence. © Schmidt et al./NJIT/NSO/AURA/NSF Until now, solar telescopes have used adaptive optics mainly to study the Sun’s surface, the release stated. Observing the fainter corona has remained a challenge, with coronal features blurred to scales of 621 miles (1,000 kilometers)—a limit that’s existed for 80 years. But Cona now resolves features down to just 39 miles (63 km), the theoretical limit of the Goode telescope.

Among the new footage captured by the team are shots of a twisting solar prominence reshaping in real time, spicules flickering on the surface, and fine, hair-like strands of coronal rain narrower than 12.5 miles (20 km). When you consider how far the Sun is from Earth, how faint the corona is relative to the rest of the star, and how much of Earth’s turbulent atmosphere the team had to cut through and correct for, the sharpness of the images is a triumph.

“This transformative technology, which is likely to be adopted at observatories world-wide, is poised to reshape ground-based solar astronomy,” said study co-author Philip Goode, a physicist at NJIT-CSTR, in the same release. “With coronal adaptive optics now in operation, this marks the beginning of a new era in solar physics, promising many more discoveries in the years and decades to come.”

The observations offer crucial data for unraveling enduring solar mysteries—like why the corona is millions of degrees hotter than the solar surface.

The team plans to bring the coronal adaptive optics technology to the 13-foot (4-meter) Daniel K. Inouye Solar Telescope in Hawaiʻi—potentially revealing even smaller details of the Sun’s atmosphere.