Nebulae are vast, interstellar clouds of gas and dust that are scattered throughout the galaxy. These clouds are primarily made up of hydrogen gas, which is ionized by the intense radiation from nearby stars. As a result, many nebulae emit light in the form of glowing, colorful clouds that can be seen from Earth.

There are several different types of nebulae, each with their own distinct characteristics.

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Here are a few examples:

1. H II Regions: H II regions are large, glowing clouds of ionized hydrogen gas that are often found around young, massive stars. These stars emit large amounts of ultraviolet radiation, which ionizes the surrounding hydrogen gas and causes it to glow.

2. Planetary Nebulae: Planetary nebulae are formed when a low-mass star reaches the end of its life and sheds its outer layers. As the star's core collapses, it heats up and emits intense radiation that ionizes the gas in the surrounding cloud. This creates a colorful, glowing shell of gas that resembles a planet.

3. Supernova Remnants: When a massive star reaches the end of its life and explodes in a supernova, it leaves behind a cloud of gas and dust known as a supernova remnant. These clouds are incredibly hot and emit intense radiation, which ionizes the surrounding gas and creates a glowing cloud of debris.

4. Dark Nebulae: Unlike the other types of nebulae, dark nebulae do not emit light and are therefore difficult to observe. These clouds are made up of cold, dense gas and dust that block the light from stars behind them, creating a dark silhouette against the background of the Milky Way.

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Nebulae are not only beautiful to look at, but they also play an important role in the formation of new stars and planets. As clouds of gas and dust collapse under their own gravity, they can form protostars and protoplanetary disks, which eventually give rise to new planetary systems.