Domain: Natural Science — Astrophysics & Astronomy
Target concept: The comet's tail always extends away from the Sun, becoming longer and brighter as it approaches the Sun.

Video generation prompt: A comet approaches the Sun from a distant region, and the morphology and brightness variation of its tail are observed during this process.

Evaluation guide:
(i) Target concept: Radiation-driven anti-solar tail formation in comets.
Minimum mechanism: Solar photons and charged particles exert net outward force on released volatiles/dust; tail direction is determined solely by instantaneous Sun-comet vector, not comet velocity vector.
(ii)Storyline: Frame 1: Distant comet with barely visible tail aligned anti-solar. → As comet advances, solar flux increases → tail material sublimates and is accelerated outward → tail lengthens visibly and gains luminance via scattering/emission. → Tail orientation continuously updates to remain colinear and opposite to Sun-comet line. → No tail reversal or Sun-ward pointing occurs at any point; tail remains causally locked to solar position and intensity. Perspective: Fixed wide-angle view showing both Sun and full tail path; no occlusion; Sun must remain visually dominant and stationary; comet must remain fully visible and resolvable as a distinct nucleus+coma+tail system throughout.

Manual:
Experimental Procedure
1. Position Sun at fixed location (center-right).
2. Place comet far from Sun (left edge) with initial short/faint tail pointing away.
3. Animate comet moving steadily rightward toward Sun over 10 seconds.
Observation of Experimental Phenomena
- Tail continuously extends longer and becomes brighter as comet approaches Sun.
- Tail always points directly away from Sun — never sideways or toward it — and rotates dynamically to maintain that orientation.
Summary of Experimental Principles
- A comet’s tail is formed by solar radiation pressure and solar wind acting on volatile ices and dust; it always points away from the Sun regardless of comet’s direction of motion.

Prompt Grounding rubric:
level_1: No comet is shown, no Sun is shown, neither body moves at all, or the video does not depict a tail or any approach toward the Sun.
level_2: Both a comet and a Sun-like body are present but stay static with no visible approach; the comet has no visible tail, or the tail appears in a location unconnected to the comet itself (e.g., floating apart from the nucleus or attached to the Sun instead); the tail's length and brightness never appear to change.
level_3: A comet (with a visible head/coma) and a Sun-like body are both present; the comet visibly moves closer to the Sun over the course of the video; a tail extends from the comet's nucleus and is present for at least part of the video, though it may hold one fixed on-screen orientation without ever visibly swinging around as the comet moves.
level_4: Everything in Level 3 holds, AND the tail stays continuously attached to and extending from the comet's nucleus throughout the whole approach (never fully vanishing then reappearing); the tail's on-screen length and brightness both noticeably increase somewhere over the course of the video, even if that increase happens as one visible jump rather than a gradual build.
level_5: Everything in Level 4 holds, AND the tail remains visibly attached to the nucleus in every frame with no flicker, no momentary disappearance, and no gap between comet and tail; its on-screen length and brightness increase in a smooth, gradual, and unbroken progression rather than in discrete jumps, across the entire approach sequence.

Scientific and Causal Correctness rubric:
level_1: The tail points toward the Sun, or its direction seems unrelated to the Sun's position; the tail gets shorter or dimmer as the comet nears the Sun; or the tail is present before the comet is anywhere near the Sun or lingers unchanged with no connection to the approach.
level_2: The tail points away from the Sun in some frames but toward it or off to the side in others; the tail's growth in length or brightness runs opposite to what approach should cause (e.g., it shrinks during approach, or only changes right at the very start or very end); nothing on screen ties the tail's growth to how close the comet has gotten to the Sun.
level_3: The tail consistently points away from the Sun in every frame; its length and brightness increase only while the comet is getting closer to the Sun, though the growth may kick in late (staying nearly unchanged until the comet is close to the Sun) or happen in a couple of abrupt jumps rather than building steadily.
level_4: Everything in Level 3 holds, AND the tail's length and brightness build up progressively as the comet approaches, with no reversal or sideways drift in its orientation at any point; the only shortfall is that the tail's first appearance is a bit delayed relative to when growth should plausibly begin, or its brightening happens in a couple of distinct steps rather than one smooth ramp.
level_5: The tail points away from the Sun in every single frame with no exception; it becomes visible early in the approach and its length and brightness then increase continuously and smoothly as the comet-Sun distance shrinks, with no frame showing the tail misaligned, reversed, paused, or momentarily shrinking.

Spatiotemporal Consistency rubric:
level_1: The comet or the Sun jumps to a new position with no motion in between; the tail appears or disappears in a single instant rather than fading or growing in; the Sun's brightness flicks on or off with no transition; the comet's shape breaks or deforms unnaturally; or the background stars flicker or warp.
level_2: The comet's motion is jerky, with at least two visible pauses or stutters as it moves; the tail blinks out for at least one frame and then comes back; the Sun's position shifts relative to the background stars; or the lighting/shading on the comet changes in a way that does not match its motion.
level_3: The comet follows one continuous path toward the Sun; the tail grows continuously out of the nucleus with no gaps; the lighting on the comet stays consistent with a single fixed Sun position and viewing angle; the only shortfall is a minor tail-rendering issue such as brief flickering at its edge, slight warping, or the tail's base appearing to wobble slightly as the comet's orientation shifts.
level_4: Everything in Level 3 holds, AND the comet keeps a stable shape, size, and orientation throughout its motion; the tail stays anchored to the nucleus with no slipping, warping, or flicker; lighting and shading stay spatially coherent with the Sun's fixed position; the only remaining flaw, if any, is the tail's length change trailing slightly behind the comet's positional change.
level_5: The comet's entire trajectory is smooth and unbroken from start to finish; the tail's growth, brightening, and reorientation track the comet's motion and the Sun's position in close synchrony with no flicker, jitter, warping, or lighting mismatch; the comet's structure never deforms and the background stars never distort at any point.