A collection of thousands and millions of stars is called a galaxy.
Supplementary
Quantification, although the collection process could be called data collection (just a guess :)
When two rays are joined at their endpoints, the resulting figure is called an angle. The point where the rays meet is known as the vertex, while the rays themselves are referred to as the sides of the angle. Angles can be measured in degrees to indicate their size.
space
A collection of rays is called a ray bundle.
A collection of rays of light is called a beam or a ray bundle.
rainbow
The collection of wavelengths is called the electromagnetic spectrum. It includes all forms of electromagnetic radiation, from radio waves to gamma rays.
The electromagnetic spectrum.
Light rays coming in are called incident light rays.
they are called UV, or Ultraviolet rays.
At collection of stamps is refered to as a stamp collection. They are frequently kept in albums. Philately is the name for the study and collection of stamps.
The light rays that bounce back are called reflected light rays.
it is called a range of mountains
a collection of fish is called a school of fish
A collection of fish is called a school.