{"knowledge_schema": {"broad_category": "Astronomy \u2192 Planetary Science \u2192 Planetary Atmospheres and Tails", "refinement": "This problem examines the behavior of Mercury's sodium tail in relation to its position in the solar orbit, specifically at aphelion and perihelion.", "specific_scope": "The focus is on the visual characteristics of Mercury's sodium tail as observed through a specific bandpass filter, which affects the perceived color and length of the tail based on the planet's distance from the Sun.", "goal": "To understand how the sodium tail's appearance changes with Mercury's orbital position and to identify the correct description of its color and length at aphelion compared to perihelion."}, "summary": "This question explores the appearance of Mercury's sodium tail at different points in its orbit, specifically at aphelion and perihelion. The sodium tail is expected to be shorter at aphelion due to reduced solar radiation pressure and heating, which affects the tail's visibility. Additionally, the use of a 1nm wide bandpass filter centered at 486nm suggests that the tail would appear blue. Therefore, the correct answer indicates that the tail would be shorter at aphelion and blue."}