A nebula is a massive cloud of gas (mostly hydrogen and helium) and dust in space, often serving as a nursery for new stars. Nebulae are key sites in the process of star formation and are fundamental to the life cycle of stars in the universe. Nebulae can vary greatly in size and appearance, and they come in different types based on their properties.

• Emission Nebula: These glow brightly, emitting light due to the ionization of gas by nearby hot stars (e.g. the Orion Nebula).
• Reflection Nebula: These don’t emit their own light but reflect the light of nearby stars (e.g. the Witch Head Nebula).
• Dark Nebula: Thick clouds of dust that block the light from stars behind them, making them appear as dark patches in space (e.g. the Horsehead Nebula).
• Planetary Nebula: The remnants of dying stars that have shed their outer layers (e.g. the Ring Nebula).
• Supernova Remnant: Formed from the explosive death of a massive star, leaving behind a nebula of gas and dust (e.g. the Crab Nebula).