Non-Luminous Celestial Bodies

Planets are non-luminous in nature. They do not emit their own light and are only visible as they reflect the light of the star they orbit around.

Stars:
- Stars are celestial bodies that emit their own light due to nuclear reactions happening in their core.
- They are classified based on their brightness, size, and temperature.
- Some of the common types of stars include Red Giants, White Dwarfs, and Neutron Stars.

Planets:
- Planets are celestial bodies that orbit around a star due to the gravitational pull of the star.
- They are non-luminous in nature and do not emit their own light.
- They are only visible as they reflect the light of the star they orbit around.
- There are eight planets in our solar system, namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Nebula:
- Nebulae are interstellar clouds of dust, hydrogen, helium, and other ionized gases.
- They are luminous in nature and emit light due to ionization and excitation of gases by radiation from nearby stars.
- They are of different types, such as emission, reflection, and dark nebula, depending on their properties.

Conclusion:
In conclusion, planets are non-luminous celestial bodies as they do not emit their own light and are only visible as they reflect the light of the star they orbit around. On the other hand, stars emit their own light due to nuclear reactions happening in their core, and nebulae emit light due to ionization and excitation of gases by radiation from nearby stars.