The European Space Agency has reported an image from the Trisat-S nanosatellite in which the Sun appears as a bright circle with a small black dot at its centre. According to ESA, the dark spot is not a camera failure but an expected sensor behaviour under extreme illumination known as the Black Sun effect, in which over-saturated pixels make very bright areas appear dark.

Iztok Kramberger, principal investigator of the Trisat programme at the University of Maribor in Slovenia, said the effect is a useful visual feature for the team. Together with observations of Earth and the Moon, it serves as a visual reference a spacecraft can use to determine its attitude and orbit. The team had already investigated the effect with its earlier Trisat-R mission, supported by ESA's General Support Technology Programme.

Trisat-S, led by the University of Maribor with Slovenian space company SkyLabs, carries six miniature cameras covering the satellite's surroundings in all directions. Kramberger said the mission collects simultaneous observations from low Earth orbit that can be compared with ground-based simulations. The mission is also demonstrating spacecraft hibernation technologies for future long-duration missions. ESA said Trisat-S was one of six commercial and educational CubeSats launched on Isar Aerospace's Spectrum launcher in September 2026.