The correct answer is option 3: Jupiter. A luminous object is defined as something that emits its own light, like the Sun. The Sun is a luminous object as it emits light and heat through the process of nuclear fusion. Proxima Centauri and Alpha Centauri are also luminous objects, as they are both stars that emit their own light.

On the other hand, Jupiter is not a luminous object because it does not emit its own light. Jupiter is a giant gas planet primarily made up of hydrogen and helium. Its brightness is due to reflected sunlight, similar to how the Moon appears bright in the night sky. Jupiter reflects the light it receives from the Sun, but it does not produce its own light like a star or the Sun. Therefore, option 3, Jupiter, is the correct answer as it is not a luminous object.