Classification – Odd one out (celestial objects vs sky as region): Pick the outlier: Sky, Star, Planet, Comet.

Introduction / Context:
Astronomy vocabulary distinguishes between celestial objects and the overarching region in which they appear. Three options are discrete celestial bodies; one is the visible expanse (region), not a body.

Given Data / Assumptions:

• Star → luminous celestial body.
• Planet → non-luminous body orbiting a star.
• Comet → icy body with coma/tail near the sun.
• Sky → the dome/expanse we see, not an object.

Concept / Approach:
Separate “object” from “region.” The non-object is the outlier.

Step-by-Step Solution:
Star, Planet, Comet → celestial objects.Sky → region/background.

Verification / Alternative check:
Even poetic uses of “sky” don’t render it a discrete body like a planet or star.

Why Other Options Are Wrong:

• Star, Planet, Comet are concrete astronomical objects.

Common Pitfalls:
Assuming anything visible above is a “celestial object.”

Final Answer:
Sky