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By NASA
5 Min Read Planetary Alignment Provides NASA Rare Opportunity to Study Uranus
Artist's illustration showing a distant star going out of sight as it is eclipsed by Uranus – an event known as a planetary stellar occultation. Credits: NASA/Advanced Concepts Laboratory When a planet’s orbit brings it between Earth and a distant star, it’s more than just a cosmic game of hide and seek. It’s an opportunity for NASA to improve its understanding of that planet’s atmosphere and rings. Planetary scientists call it a stellar occultation and that’s exactly what happened with Uranus on April 7.
Observing the alignment allows NASA scientists to measure the temperatures and composition of Uranus’ stratosphere – the middle layer of a planet’s atmosphere – and determine how it has changed over the last 30 years since Uranus’ last significant occultation.
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This rendering demonstrates what is happening during a stellar occultation and illustrates an example of the light curve data graph recorded by scientists that enables them to gather atmospheric measurements, like temperature and pressure, from Uranus as the amount of starlight changes when the planet eclipses the star.NASA/Advanced Concepts Laboratory “Uranus passed in front of a star that is about 400 light years from Earth,” said William Saunders, planetary scientist at NASA’s Langley Research Center in Hampton, Virginia, and science principal investigator and analysis lead, for what NASA’s team calls the Uranus Stellar Occultation Campaign 2025. “As Uranus began to occult the star, the planet’s atmosphere refracted the starlight, causing the star to appear to gradually dim before being blocked completely. The reverse happened at the end of the occultation, making what we call a light curve. By observing the occultation from many large telescopes, we are able to measure the light curve and determine Uranus’ atmospheric properties at many altitude layers.”
We are able to measure the light curve and determine Uranus' atmospheric properties at many altitude layers.
William Saunders
Planetary Scientist at NASA's Langley Research Center
This data mainly consists of temperature, density, and pressure of the stratosphere. Analyzing the data will help researchers understand how the middle atmosphere of Uranus works and could help enable future Uranus exploration efforts.
To observe the rare event, which lasted about an hour and was only visible from Western North America, planetary scientists at NASA Langley led an international team of over 30 astronomers using 18 professional observatories.
Kunio Sayanagi, NASA’s principal investigator for the Uranus Stellar Occultation Campaign 2025, meeting virtually with partners and observing data from the Flight Mission Support Center at NASA’s Langley Research Center in Hampton, Virginia during Uranus’ stellar occultation event on April 7, 2025.NASA/Dave MacDonnell “This was the first time we have collaborated on this scale for an occultation,” said Saunders. “I am extremely grateful to each member of the team and each observatory for taking part in this extraordinary event. NASA will use the observations of Uranus to determine how energy moves around the atmosphere and what causes the upper layers to be inexplicably hot. Others will use the data to measure Uranus’ rings, its atmospheric turbulence, and its precise orbit around the Sun.”
Knowing the location and orbit of Uranus is not as simple as it sounds. In 1986, NASA’s Voyager 2 spacecraft became the first and only spacecraft to fly past the planet – 10 years before the last bright stellar occultation occured in 1996. And, Uranus’ exact position in space is only accurate to within about 100 miles, which makes analyzing this new atmospheric data crucial to future NASA exploration of the ice giant.
These investigations were possible because the large number of partners provided many unique views of the stellar occultation from many different instruments.
NASA planetary scientist William Saunders and Texas A&M University research assistant Erika Cook in the control room of the McDonald Observatory’s Otto Struve Telescope in Jeff Davis County, Texas, during the Uranus stellar occultation on April 7, 2025.Joshua Santana Emma Dahl, a postdoctoral scholar at Caltech in Pasadena, California, assisted in gathering observations from NASA’s Infrared Telescope Facility (IRTF) on the summit of Mauna Kea in Hawaii – an observatory first built to support NASA’s Voyager missions.
“As scientists, we do our best work when we collaborate. This was a team effort between NASA scientists, academic researchers, and amateur astronomers,” said Dahl. “The atmospheres of the gas and ice giant planets [Jupiter, Saturn, Uranus, and Neptune] are exceptional atmospheric laboratories because they don’t have solid surfaces. This allows us to study cloud formation, storms, and wind patterns without the extra variables and effects a surface produces, which can complicate simulations very quickly.”
On November 12, 2024, NASA Langley researchers and collaborators were able to do a test run to prepare for the April occultation. Langley coordinated two telescopes in Japan and one in Thailand to observe a dimmer Uranus stellar occultation only visible from Asia. As a result, these observers learned how to calibrate their instruments to observe stellar occultations, and NASA was able to test its theory that multiple observatories working together could capture Uranus’ big event in April.
Researchers from the Paris Observatory and Space Science Institute, in contact with NASA, also coordinated observations of the November 2024 occultation from two telescopes in India. These observations of Uranus and its rings allowed the researchers, who were also members of the April 7 occultation team, to improve the predictions about the timing on April 7 down to the second and also improved modeling to update Uranus’ expected location during the occultation by 125 miles.
This image of Uranus from NIRCam (Near-Infrared Camera) on NASA’s James Webb Space Telescope exquisitely captures Uranus’s seasonal north polar cap and dim inner and outer rings. This Webb image also shows 9 of the planet’s 27 moons – clockwise starting at 2 o’clock, they are: Rosalind, Puck, Belinda, Desdemona, Cressida, Bianca, Portia, Juliet, and Perdita.NASA, ESA, CSA, STScI Uranus is almost 2 billion miles away from Earth and has an atmosphere composed of primarily hydrogen and helium. It does not have a solid surface, but rather a soft surface made of water, ammonia, and methane. It’s called an ice giant because its interior contains an abundance of these swirling fluids that have relatively low freezing points. And, while Saturn is the most well-known planet for having rings, Uranus has 13 known rings composed of ice and dust.
Over the next six years, Uranus will occult several dimmer stars. NASA hopes to gather airborne and possibly space-based measurements of the next bright Uranus occultation in 2031, which will be of an even brighter star than the one observed in April.
For more information on NASA’s Uranus Stellar Occultation Campaign 2025:
https://science.larc.nasa.gov/URANUS2025
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Charles Hatfield
Langley Research Center, Hampton, Virginia
757-262-8289
charles.g.hatfield@nasa.gov
About the Author
Charles G. Hatfield
Science Public Affairs Officer, NASA Langley Research Center
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Last Updated Apr 22, 2025 Related Terms
General Ice Giants Langley Research Center Planetary Science Division Uranus Explore More
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By NASA
4 Min Read Science Meets Art: NASA Astronaut Don Pettit Turns the Camera on Science
NASA astronaut Don Pettit is scheduled to return home in mid-April after a seven-month mission aboard the International Space Station as part of Expedition 72. Throughout his stay, Pettit contributed to research that benefits humanity and future space missions.
Pettit also shared what he calls “science of opportunity” to demonstrate how experimenting with our surroundings can help gain a better understanding of how things work. This understanding is perhaps enhanced when art, science, and microgravity come together.
Electrostatic Displays
NASA astronaut Don Pettit demonstrates electrostatic forces using charged water droplets and a knitting needle made of Teflon. This series of overlapping frames displays the unique attraction-repulsion properties of Teflon and charged droplets, similar to how charged particles from the Sun behave when they come in contact with Earth’s magnetic field. Highly energetic particles from space that collide with atoms and molecules in the atmosphere create the aurora borealis.
Specialized Equipment for Superb Science
NASA astronaut Don Pettit snaps an image of the hands of NASA astronauts Nick Hague, left, and Suni Williams inside the Life Science Glovebox, a facility at the International Space Station that separates the science from the scientists, thus protecting both from contamination.
The freezers on the International Space Station are as crucial as its experiment modules, preserving samples for further analysis on Earth. The Minus Eighty-Degree Laboratory Freezer for International Space Station stores samples at ultra-cold temperatures. NASA astronaut Don Pettit used it to freeze thin ice wafers, which he photographed with a polarizing filter to reveal unique crystal structures.
New Tech Roll-Out
NASA astronaut Don Pettit films a time-lapse sequence of Canadarm2 retrieving Materials International Space Station Experiment (MISSE-20-Commercial) samples at the International Space Station. This investigation exposed various experiments to the harsh space environment, such as vacuum, radiation, and extreme temperatures. Findings could help in many areas, from designing more durable materials to advancing quantum communications.
A surge in International Space Station research supports NASA’s exploration efforts at the Moon and beyond, requiring more energy to operate the orbiting laboratory. NASA astronaut Don Pettit photographs new and old solar arrays side by side. The technology used by the International Space Station Roll-Out Solar Arrays (IROSA) on the right was first tested aboard the station in 2017. By 2023, six IROSAs were deployed aboard station, providing a 20-30% increase in power for research and operations. Roll-Out Solar Arrays were also used on NASA’s DART asteroid mission and now are slated for the Gateway lunar outpost, a vital component of Artemis.
Squire for Spacewalks
I am the nameless boy who stays in the confines of the tent helping the Knights suit up for battle. I remain in the airlock, preparing these knights for a walk outside.
Don Pettit
"Space Squire" posted to X
NASA astronaut Don Pettit helped his colleagues suit up for two spacewalks in January. The first spacewalk involved patching the Neutron Star Interior Composition Explorer (NICER), a telescope that measures X-rays from neutron stars and other cosmic objects. Sunlight interference affected data collection, and the patches reduced this issue. On the second spacewalk, astronauts collected samples from the exterior of the International Space Station for ISS External Microorganisms. This investigation examines whether the orbiting laboratory releases microbes, how many, and how far these may travel. Findings could inform the design of future spacecraft, including spacesuits, to limit biocontamination during future space missions.
Photography with a Spin
NASA astronaut Don Pettit photographs “cosmic colors at sunrise.” From 250 miles above, the International Space Station’s orbital path covers most of Earth’s population, offering valuable data and a great opportunity for shooting breathtaking photography.
NASA astronaut Don Pettit leveraged his stay aboard the International Space Station to photograph our planet with an artistic twist.
NASA astronaut Don Pettit wrote on social media about his snapshot of the Mediterranean Sea from the International Space Station, “Sun glint off the Mediterranean Sea (infrared and converted to black and white). When the Sun reflects off the ocean, watery details unseen with normal lighting appear. Small centimeter differences in ocean height become visible, revealing hidden currents.”
NASA astronaut Don Pettit’s photography could contribute to the study of transient luminous events, colorful electrical discharges that occur above thunderstorms. His imagery can be paired with data from the Atmosphere-Space Interactions Monitor (ASIM) and Thor-Davis, a high-speed thunderstorm camera. The combined efforts of crew photography and instruments aboard the International Space Station help scientists better understand thunderstorms and their impacts on Earth’s upper atmosphere.
More of Pettit’s photography can be found on his X profile, @astro_Pettit.
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Last Updated Apr 17, 2025 Related Terms
ISS Research Donald R. Pettit Expedition 72 Humans in Space International Space Station (ISS) Keep Exploring Discover More Topics From NASA
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By European Space Agency
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By European Space Agency
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In this miniseries, we take you on a journey through the ESA Astronaut Reserve, diving into the first part of their Astronaut Reserve Training (ART) at the European Astronaut Centre (EAC) near Cologne, Germany. Our “ARTists” are immersing themselves in everything from ESA and the International Space Station programme to the European space industry and institutions. They’re gaining hands-on experience in technical skills like spacecraft systems and robotics, alongside human behaviour, scientific lessons, scuba diving, and survival training.
ESA’s Astronaut Reserve Training programme is all about building Europe’s next generation of space explorers—preparing them for the opportunities of future missions in Earth orbit and beyond.
This interview was recorded in November 2024.
You can listen to this episode on all major podcast platforms.
Keep exploring with ESA Explores!
Learn more about Arnaud’s PANGAEA training here.
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