Question

Which of the following is a non-luminous body?
(A). The Sun
(B). A star
(C). A planet
(D). All of these

Answer 1

- Hint: A luminous object is defined as an object which creates light. Therefore, a non-luminous body is a body which cannot emit or produce light on its own. From the given options, pick out the bodies which produce light on its own and which cannot.

Complete step-by-step solution -
A luminous object is defined as an object that emits light on its own. And a non-luminous object is one which is incapable of producing its own light. If we observe our daily surroundings, we will observe that the major source of light on Earth is the Sun. The sun is the star at the centre of our solar system. The Sun constantly emits light as the result of continuous nuclear fusion on its surface.
Since, the sun is a star, it is understood that all the stars emit light and therefore are luminous. Now, let us contemplate if a planet is a luminous or a non-luminous object. Again, observe your surroundings. Earth is a planet. Does it emit its own light? The answer to that question is no. Earth or in fact any planet does not emit light on its own.
Therefore, the answer to this question is C. A planet.

Note: Celestial objects like Venus, a planet and the Moon, a natural satellite of Earth, appear to shine, that seem to emit light, in the sky just like other stars. But, note that they in fact do not emit light on their own but reflect it from the Sun.