How many different types of radiation make up the electromagnetic spectrum?

Answer 1

The EM spectrum extends infinitely in either direction, up past the super-high frequency gamma rays and down past sub-hertz frequency radio waves.

However, there is probably a practical limit to the upper frequency of radiation in the Planck distance--In the discrete model of space-time, nothing can exist at any size smaller than this, so this establishes an upper limit to the frequency of radiation.

Similarly, it is unlikely that any radio wave with a wavelength larger than the breadth of the universe can exist, establishing a lower limit to the frequency of radiation.

In the continuous model of space-time, there are truly infinite wavelengths of radiation; in the discrete model, these is a finite number that is still very, very large (effectively infinite).

As far as human definitions, there are seven large categories of EM radiation: Radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray

(section moved from "Why is Snow White and water transparent but sometimes ice can be both?")

snow is white and the sky is blue and the grass is green because the UV rays from the sun is reflecting every color to an object and the object only relfects one of those colors, the color that you see. so grass is green because it relefcts the color green when UV rays hit it. same goes for snow being white and water bing clear and ice being white or a trasparent-ish blue.

Point of Accuracy

UV radiation is only one part of the electromagnetic spectrum. This is broken up into several different parts;

Gamma radiation

X-Ray radiation

Ultraviolet radiation

Visible Light

Infrared radiation

Microwave radiation

Radio waves.

Of these different types of radiation the type that gives grass it's green colour and the sky its blue colour is the visible spectrum. UV radiation cannot be seen directly. It is seen most often when white is made to fluoresce under a blacklight. As was said above though the reason grass is green is because it reflects the green region of the visible light spectrum.