A Stellar Occultation Just Occurred With Uranus
- Editor OGN Daily
- Apr 26
- 2 min read
A stellar occultation happens when a planet’s orbit brings it between Earth and a distant star, and it's an opportunity for scientists to improve their understanding of that planet’s atmosphere and rings.
Such an event happened with Uranus earlier this month and it’s more than just a cosmic game of hide and seek. Observing the alignment allows NASA scientists (in partnership with an international team of over 30 astronomers using 18 professional observatories) 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.
“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.”
Analyzing the data will help researchers understand how the middle atmosphere of Uranus works and could help enable future Uranus exploration efforts, says NASA.
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.
What to Call a Probe Going to Uranus? Asking the public to name such an expedition may have been a mistake.
