By Richard D. Jacobs, M.D.
Nebulae are collections of gas in space. Diffuse Nebulae have no one characteristic shape. The colors seen in nebulae depend on the gases that are present and the temperature of the gases. Pinkish red comes from the glow of hydrogen, the most common element in the universe. Greens and blues can come from ionized oxygen or even helium. Nebulae are often the "birth places" of stars. Diffuse Nebulae can beemission nebulae, which are hot and give off their own light, or reflection nebula, which are cold gases or dust and are illuminated by star light, just as the headlights of your car cause ground fog to brighten. Dark nebulae (called“Barnard Nebulae”) are made from dust that block light. These are seen when they are highlighted against bright emission or reflection nebula. When all these different kinds of nebulae are mixed together in a single space object (see B33,Horsehead Nebula, below), the result is a complex work of celestial art. All of the nebulae seen on this website are located in our own Milky Way Galaxy.