An optical illusion known as the "lunar terminator paradox" describes why the moon's illuminated portion sometimes appears to point opposite the sun's position. After sunset, observers expect the lit side to face the sun below the horizon, but often see it pointing upward. A camper in the mountains observed this firsthand, noting a full moon on the horizon appears fully lit, while a higher moon reveals a dark bottom slice.

The effect occurs because viewers look up at the moon from below. As the moon rises from the horizon, more of its dark side becomes visible, making it appear to "point up." Even at sunset, a 3/4-lit moon shows this effect. Researchers found AI tools like Claude and Gemini failed to explain the phenomenon, producing circular arguments despite reading available explanations, highlighting a current limitation in AI reasoning capabilities regarding spatial optics.

AGI is not yet achieved.