A stunning visual phenomenon – a lunar halo – was captured by an astronaut aboard the International Space Station on December 25, 2025, offering a rare glimpse into the intricacies of Earth’s upper atmosphere. The image, taken above the Indian Ocean, showcases the delicate arc of light created when moonlight refracts through ice crystals at altitudes exceeding 50 miles. This observation highlights the ongoing work of the ISS Crew earth Observations Facility, which provides vital data for atmospheric research and public understanding of our planet’s complex systems.
An astronaut aboard the International Space Station (ISS) captured a rare optical phenomenon – a “Lunar Halo” – while orbiting above the Indian Ocean. The striking image reveals a delicate arc of light appearing to float above the Earth’s blue horizon, seemingly detached from the planet itself.
The observation, documented on December 25, 2025, stems from the refraction of moonlight by ice crystals in the extremely high layers of the Earth’s atmosphere, where air density is drastically reduced. The ISS’s low Earth orbit provides a unique vantage point, positioning the moon behind the atmosphere relative to the camera, causing the moonlight to bend and spread into the luminous arc.
The observation was led by the ISS Crew Earth Observations Facility at NASA’s Johnson Space Center. This program focuses on documenting atmospheric conditions, land features, bodies of water, and Earth lights through astronaut photography for both scientific research and public outreach. The detailed imagery collected contributes to a broader understanding of our planet’s dynamic systems.
Orbiting at an altitude of over 200 miles, the ISS’s orbital geometry occasionally places the moon directly behind the atmosphere. This allows the atmospheric layers to act as a natural lens, reshaping the moonlight.
The photograph also clearly illustrates the distinct layers of the atmosphere, ranging from the orange-hued troposphere to the pale white stratosphere and the deep blue upper atmosphere. Above this lies the mesosphere, a frigid region extending approximately 30–54 miles above the surface, which can sometimes contain rare ice formations.
Lunar Halos form when moonlight passes through ice crystals, undergoing refraction and a slight separation of colors. Typically, a halo appears as a ring with a radius of about 22 degrees around the moon. However, in this instance, only an arc of light is visible because the ice crystals don’t fully encircle the moon from the ISS’s perspective.
Researchers explain that the orientation and shape of the ice crystals significantly influence the halo’s appearance. Hexagonal plate and column-shaped crystals refract light differently, meaning even small changes in crystal angle can result in a partial halo.
Ice at such extreme altitudes is relatively uncommon. Recent research indicates that the highest atmospheric ice layers form in the coldest summer regions, around 50 miles above the surface. These layers are highly sensitive to even minor temperature fluctuations and gravitational waves originating from storms and terrain below.
Years of satellite observations have demonstrated a strong correlation between these luminous nighttime ice formations and the lower atmosphere. This connection helps explain why the Lunar Halo in the photograph appears near the peak of the blue atmospheric layer, rather than in the more common lower clouds.
Although the moon was in a young crescent phase during the image capture, the camera’s exposure settings made the entire disk appear bright. This effect was further enhanced by earthshine – sunlight reflected from Earth onto the dark side of the moon, making it appear fuller than its actual phase.
NASA considers the photo a demonstration of the value of visual observations made by astronauts. Beyond capturing moments often missed by automated sensors, the images provide a direct view of the interplay between optics, weather, and atmospheric chemistry on a planetary scale.
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