A rare astronomical alignment on April 7, 2025, presented NASA with a unique chance to study the atmosphere and rings of Uranus through a phenomenon known as a stellar occultation. As Uranus passed in front of a star approximately 400 light-years away, its atmosphere caused the starlight to refract and dim, creating a “light curve” that scientists can analyze to extract critical information about the planet’s stratosphere, including temperature, density, and pressure.
This alignment marks the most significant observational opportunity since the last bright stellar occultation by Uranus in 1996. According to NASA’s Langley Research Center, over 30 astronomers from 18 observatories across Western North America collaborated on the Uranus Stellar Occultation Campaign 2025. Their goal: gather precise measurements that can refine our understanding of the planet’s atmospheric structure, ring dynamics, and even its orbital position, which is currently known only to within about 100 miles.
Stellar Occultation: A Glimpse Into Uranus’s Middle Atmosphere
When Uranus moved in front of the background star, the refracted starlight revealed important details about the planet’s stratosphere—a layer that sits between the upper atmosphere and the lower weather systems. As William Saunders, the lead investigator from NASA Langley, explained, observing this light curve from multiple vantage points allows scientists to “measure the light curve and determine Uranus’s atmospheric properties at many altitude layers.” This is particularly important because it’s only the second time in nearly 30 years that scientists have had such a clear look at the ice giant’s middle atmosphere.
In addition to its significance for atmospheric research, the occultation has refined our models of Uranus’s orbit, contributing to better navigation data for future missions. While Voyager 2 remains the only spacecraft to have visited Uranus (in 1986), the new data could help justify and guide upcoming Uranus-focused missions—some of which are already under discussion for the 2030s.
Massive Collaborative Effort Across the Globe
The success of the April 7 observation hinged on a global collaboration. Leading up to the main event, NASA tested its strategies during a November 2024 occultation, visible only from Asia. Observatories in Japan, Thailand, and India participated, helping NASA refine timing predictions and calibrate instruments for April’s alignment. These practice runs ensured that all 18 observatories were well-coordinated, and even allowed astronomers to update Uranus’s predicted location by 125 miles, a level of precision crucial for accurate data collection.
Among those involved was Emma Dahl, a postdoctoral scholar at Caltech, who assisted with observations from NASA’s Infrared Telescope Facility (IRTF) in Hawaii. “As scientists, we do our best work when we collaborate,” she said. “The atmospheres of gas and ice giants offer unique opportunities because they lack solid surfaces, allowing us to study cloud dynamics and atmospheric layers without interference.”
