Classification (luminous vs non-luminous celestial bodies): Three objects shine by reflected sunlight; one object produces its own light. Identify the odd one out.

Introduction / Context:
Astronomy-themed classification often distinguishes intrinsic from apparent brightness. Non-luminous bodies like planets and satellites are visible because they reflect sunlight, whereas stars emit their own light via nuclear fusion. Recognizing this physical difference is fundamental in basic space science and prevents common confusions about why objects like the Moon and Venus are bright in the night sky.

Given Data / Assumptions:

• Sun → star; emits light and heat through fusion reactions.
• Moon → natural satellite; shines by reflecting sunlight.
• Venus → planet; highly reflective atmosphere causes high apparent brightness.
• Mars → planet; visibility due to reflected sunlight from its surface/atmosphere.

Concept / Approach:
Divide the set into luminous (self-luminous) vs non-luminous (reflective). The only self-luminous item in the options is the Sun. All the others are non-luminous and only visible because of the Sun’s illumination, which establishes a clean 3-to-1 split suitable for an “odd one out” problem.

Step-by-Step Solution:

Verification / Alternative check:
A quick rule: if an object can be seen in broad daylight because it emits intense light, it is likely a star (here, the Sun). Planets and the Moon are not visible by self-emission.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing brightness with luminosity: Venus appears very bright but is still non-luminous. Brightness alone is not proof of self-emission.

Final Answer:
Sun