Like stars, nebulas give off light, but they have no light energy of their own.  Sometimes there are stars fixed firmly in the nebula that have surface temperatures of 20,000° Celsius to 40,000° Celsius, or 36,000° Fahrenheit to 72,000° Fahrenheit (Water freezes at 32° Fahrenheit, which is 0° Celsius).  These stars give off ultraviolet radiation that is absorbed by the nebula’s gas and reradiated, partly as visible light.  One striking feature of some planetary nebulas is the form shown by separating light, the way that sunlight is separated by water after it rains in the form of a rainbow.  A spectrograph is used to gain images of nebulas in each particular radiation it gives off.  The ghostly lines seen in a gaseous nebula are all due to large elements of argon, hydrogen, sulfur, helium, neon, nitrogen and oxygen.