December 26, 2025 | 07:00 pm
TEMPO.CO, Jakarta - An astronaut aboard the International Space Station (ISS) has captured a rare optical phenomenon known as a lunar halo while orbiting above the Indian Ocean. The striking image shows a thin, glowing arc suspended above the blue edge of Earth, appearing almost detached from the planet.
According to Earth Observatory on December 25, 2025, the phenomenon occurred when moonlight was refracted by ice crystals in the uppermost layers of Earth’s atmosphere, where the air is extremely thin.
How the Lunar Halo Formed
From the ISS’s low-Earth orbit, the viewing geometry placed the Moon directly behind Earth’s atmosphere along the astronaut’s line of sight. This alignment caused the atmosphere to act like a natural lens, bending and spreading moonlight into a luminous arc.
The ISS orbits at an altitude of more than 200 miles (around 320 kilometers). Under certain conditions, this vantage point allows astronauts to observe atmospheric optical effects that are difficult or impossible to see from the ground.
The photograph clearly reveals multiple layers of Earth’s atmosphere. Closest to the surface is the orange-tinted troposphere, followed by the pale white stratosphere and the deep blue upper atmosphere. Above these layers lies the mesosphere, an extremely cold region located about 30 to 54 miles (50 to 85 kilometers) above Earth.
It is within this upper region that rare atmospheric ice can form, an essential ingredient in creating a lunar halo.
Why Only an Arc Appears
Typically, a lunar halo appears as a complete ring about 22 degrees around the Moon. However, in this image, only a partial arc is visible. Scientists explain that the ice crystals responsible for refracting the light did not fully surround the Moon from the ISS’s perspective.
The shape and orientation of the ice crystals, often plate-like or hexagonal columns, play a crucial role. Even small changes in their alignment can result in partial halos rather than full circles.
Rare Ice at Extreme Altitudes
Ice at such high altitudes is uncommon. Recent studies indicate that the highest ice layers in Earth’s atmosphere tend to form during the coldest summer conditions, roughly 50 miles above the surface. These layers are highly sensitive to subtle temperature shifts and atmospheric gravity waves generated by storms and terrain below.
Satellite observations have shown that these glowing ice formations are closely linked to processes in the lower atmosphere, helping explain why the halo appears near the top of the blue atmospheric layer rather than within typical cloud formations.
The Moon’s Illusion of Fullness
At the time the image was taken, the Moon was actually in a young crescent phase. However, camera exposure settings made the entire lunar disk appear bright. This effect was enhanced by earthshine, which is sunlight reflected from Earth onto the Moon’s darker side, making the Moon appear fuller than it truly was.
NASA says the image highlights the scientific importance of astronaut photography. Unlike automated sensors, astronauts can capture fleeting visual phenomena and provide direct insights into how light, weather, and atmospheric chemistry interact on a planetary scale.
The lunar halo image serves both as a scientific observation and a vivid reminder of the complex and delicate dynamics shaping Earth’s atmosphere.
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