Domain: Natural Science — Astrophysics & Astronomy
Target concept: The Moon undergoes a cyclic change in its phases, progressing from new moon to first quarter, then to full moon, and finally to last quarter.

Video generation prompt: Show the continuous variation of the lunar phase as observed from the same location on Earth.

Evaluation guide:
(i) Target concept: Apparent cyclical illumination variation of the Moon as seen from a fixed point on Earth, driven solely by orbital geometry.
Minimum mechanism: Sun is distant directional light source; Moon orbits Earth monthly; observer remains fixed on Earth surface; no atmospheric scattering or perspective distortion modeled; only geometric illumination by direct sunlight.
(ii)Storyline: Frame 1: Moon fully unlit (new), invisible or nearly so against bright sky, but retained as dark disk for visibility. → Gradual appearance of thin crescent (waxing) with convex terminator facing right. → Crescent widens to half-disk (first quarter) with near-straight terminator oriented vertically. → Lit area continues expanding to full disk (full moon), terminator vanishes. → Lit area begins shrinking: half-disk reappears (last quarter) with near-straight terminator now oriented vertically but opposite curvature. → Continues to waning crescent (concave terminator facing left); though not required for core demonstration, full cycle implies return toward new. All observed from fixed horizon-aligned viewpoint; no parallax, no libration, no Earth rotation effects.

Manual:
Experimental Procedure
1. Fix camera viewpoint to simulate observation from a stationary location on Earth"s surface (e.g., horizon + starfield background).
2. Render a single lunar disk centered in frame, maintaining constant size and position.
3. Gradually animate illumination to cycle through: new moon → first quarter → full moon → last quarter.
Observation of Experimental Phenomena
The lunar disk shows a continuous, monotonic change in lit area: starting fully dark, increasing to half-lit (first quarter), then fully lit (full), then decreasing to half-lit again (last quarter), with terminator curvature and orientation shifting correctly per phase.
Summary of Experimental Principles
The Moon undergoes a cyclic change in its phases, progressing from new moon to first quarter, then to full moon, and finally to last quarter, due to changing relative geometry of Sun–Moon–Earth.

Prompt Grounding rubric:
level_1: No moon-like disk appears anywhere in the video, or more than one celestial disk is shown at once, or there's no sense of a fixed Earth-based observing point (e.g., no dark sky or horizon context), or the disk's illumination never changes over the whole video.
level_2: A single moon disk is shown against an Earth-based night-sky backdrop, but its illuminated portion never changes, or the viewpoint shifts partway through (e.g., cutting from a ground view to a view from space).
level_3: A single moon disk stays visible the whole time against a fixed night-sky backdrop; its illuminated portion changes across at least three different phases in a sensible order (e.g., dark, to half-lit, to fully lit), but one expected phase in the new-to-first-quarter-to-full-to-last-quarter sequence is skipped or shown out of order.
level_4: A single moon disk stays visible against a fixed night-sky backdrop; the illuminated portion passes through all four phases (new, first quarter, full, last quarter) in the correct order with no extra disks or viewpoint changes, but one transition between phases happens as a sudden jump rather than a gradual change.
level_5: A single moon disk stays visible against a fixed night-sky backdrop for the whole video; the illuminated portion moves smoothly and in order through new, first quarter, full, and last quarter with no skipped phase, no repeated phase, no second disk appearing, and no viewpoint change, all within one unbroken shot.

Scientific and Causal Correctness rubric:
level_1: The disk shows lighting that could never happen physically: e.g., a crescent sliver brighter than the full disk, or the dark portion glowing on its own; or the phases skip logically (e.g., a full disk appears right after a new/dark disk with no phases shown in between); or a half-lit disk is split by a curved rather than straight line.
level_2: The disk cycles through phase-like shapes, but violates basic geometry: e.g., the 'full moon' frame is only half-lit, the 'new moon' frame still shows a lit sliver, or the light/dark boundary stays perfectly straight even during the crescent and gibbous stages, when it should visibly curve.
level_3: New moon (fully dark disk), first quarter (half-lit disk split by a straight line), and full moon (fully lit disk) are all shown correctly (the lit area grows from new to full and the boundary shape matches each stage), but the last-quarter phase is missing or shows the lit half on the wrong side.
level_4: All conditions for score 3 are met, AND all four phases show the correct boundary shape (curved for the crescent and gibbous stages, a straight line splitting the disk in half at first and last quarter), and the lit area grows to full then shrinks back in the correct order, but the straight boundary at one of the two quarter phases is tilted at a clearly wrong angle (e.g., running across the top or bottom of the disk instead of roughly top-to-bottom).
level_5: All conditions for score 4 are met, AND the light/dark boundary is correct at every phase: at first and last quarter it runs roughly vertically, splitting the disk into a lit half and a dark half on opposite sides for the two quarters; at new moon the disk shows no lit sliver at all, and at full moon it shows no dark sliver at all: no boundary line is visible inside the disk at new or full; the lit area increases without reversing from new to full, then decreases without reversing from full to last quarter.

Spatiotemporal Consistency rubric:
level_1: The moon disk jumps to a different spot in the frame between shots, changes size abruptly, spins in place unrelated to its phase change, or flickers apart; the background stars or horizon jump or distort; the direction of the moon's lit side flips instantly with no transition.
level_2: The disk stays in frame but visibly stretches, squishes, or looks blocky while its phase changes; the background stars or horizon drift noticeably or blink; the lit portion jumps straight from one shape to a very different one with no in-between frames; the light/dark boundary flickers unnaturally.
level_3: The disk keeps a steady position, size, and shape; the background stays fixed; the phase changes gradually across many frames rather than in sudden jumps, but at least one transition shows a brief hiccup: for example the light/dark boundary momentarily doubles up or the disk's edge visibly wobbles for an instant.
level_4: The disk keeps a steady position, size, and shape throughout; the background stays fixed; the phase change is continuous and gradual with no sudden jumps, doubled boundary lines, or wobble, except for one brief moment where the light/dark boundary flattens out unexpectedly before continuing to curve correctly.
level_5: The disk shows no drift in position, no change in size, no unwanted rotation, and no distortion at any point; the background stays completely static; the phase change progresses smoothly frame after frame, with the boundary shape and lit-area size always looking consistent with the frames just before and after; nothing in the video looks like a broken or mismatched step in the sequence.