Stars:

Stars are celestial bodies that emit light and heat due to the nuclear reactions occurring in their cores. They are composed primarily of hydrogen and helium gas, with trace amounts of other elements. Stars are incredibly hot and dense, and their immense gravitational pull keeps them in a spherical shape.

Key Points:
- Stars are self-luminous, meaning they generate their own light through nuclear fusion.
- They exist in various sizes, from smaller stars like red dwarfs to massive stars called giants and supergiants.
- Stars are classified based on their spectral characteristics, which determine their color and temperature.
- The Sun, which is a star, is classified as a yellow dwarf.
- Stars can be found in different stages of their evolution, such as protostars, main sequence stars, red giants, and white dwarfs.
- They are located in vast systems called galaxies, with billions of stars in each galaxy.

Planets:

Planets are celestial objects that orbit around stars or other stellar remnants. Unlike stars, planets do not produce their own light and are instead illuminated by the light of their parent star. They are typically composed of rock, metal, and gases, and have a solid surface.

Key Points:
- Planets come in various sizes, ranging from small rocky planets like Mercury and Mars to gas giants like Jupiter and Saturn.
- They have a variety of characteristics, including atmospheres, magnetic fields, and moons.
- Planets can be classified into two main types: terrestrial planets (rocky) and gas giants (primarily composed of hydrogen and helium).
- The number of known planets in the universe is constantly expanding as technology advances and new discoveries are made.
- Earth is a special planet as it supports life due to its suitable atmospheric conditions and presence of liquid water.
- Planets are part of our solar system, which consists of the Sun, eight planets, and various other celestial objects.

Differences:

The key differences between stars and planets are as follows:

1. Light Production: Stars produce their own light through nuclear fusion, while planets do not emit light and are illuminated by the light of their parent star.
2. Composition: Stars are primarily composed of hydrogen and helium gases, while planets have a combination of rock, metal, and gases.
3. Size: Stars can vary in size, ranging from small red dwarfs to massive giants and supergiants, while planets have a wide range of sizes from small rocky planets to gas giants.
4. Classification: Stars are classified based on their spectral characteristics, while planets are categorized based on their composition and characteristics.
5. Role in Systems: Stars are the central objects around which planets orbit, while planets are the satellites that revolve around stars.
6. Light Source: Stars are a primary source of light in the universe, whereas planets reflect the light of their parent star.