What is a nebula?

Types of Nebulae

1. Emission Nebulae – These nebulae glow brightly because their gas is ionized by the radiation from nearby hot stars. The high-energy ultraviolet light excites the gas, causing it to emit visible light, often appearing red or pink due to ionized hydrogen. Emission nebulae are often found in regions of active star formation. One of the most famous examples is the Orion Nebula (M42), a spectacular stellar nursery visible to the naked eye.

2. Reflection Nebulae – Unlike emission nebulae, these do not produce their own light. Instead, they scatter and reflect the light from nearby stars, often appearing blue due to the way dust particles scatter shorter wavelengths of light. Reflection nebulae are usually found in regions where young, bright stars are forming. A well-known example is the Pleiades Nebula, which surrounds the Pleiades star cluster (also known as the Seven Sisters).

3. Dark Nebulae – These are dense clouds of gas and dust that absorb and block light from stars and nebulae behind them. They appear as dark, shadowy shapes against the brighter background of the Milky Way or other celestial objects. These nebulae are rich in the raw materials needed for star formation. A striking example is the Horsehead Nebula, a dark, horse-shaped cloud in the constellation Orion.

4. Planetary Nebulae – These are the expanding outer shells of dying sun-like stars that have shed their outer layers. The exposed hot core of the dying star illuminates the gas, making it glow in different colors. Despite their name, planetary nebulae have nothing to do with planets; they were named because early astronomers mistook their round shapes for planets. A famous example is the Ring Nebula (M57), which appears as a glowing ring of gas in the constellation Lyra.

5. Supernova Remnants – These are the leftover clouds of gas and dust from a massive star’s explosive death. When a large star runs out of fuel, it collapses and triggers a supernova, sending shockwaves that expand outward and create beautiful, intricate nebulae. These remnants are crucial to the universe, as they enrich space with heavy elements needed for new star and planet formation. One of the best-known supernova remnants is the Crab Nebula (M1), which resulted from a supernova explosion recorded by Chinese astronomers in 1054 AD.

Bonus Fact!

Seeing the Orion Nebula (M42) with the Naked Eye - The Orion Nebula (M42) is one of the brightest nebulae in the night sky and is visible to the naked eye under good conditions. It appears as a faint, hazy patch in the sword of Orion, just below Orion’s Belt. The nebula is located about 1,344 light-years from Earth and is the closest major stellar nursery, where new stars are forming.