Turn on the light bulb attached to the variac. Look at a light bulb through the space between your index finger and thumb. On the figure below draw what you see . Now give a verbal description of what you saw. The one thing that man will never know is the chemical composition of the stars.
Diffraction gratings act like a prism and spread light out into a spectrum or a rainbow.
This kind of spectrum is called a continuous spectrum. This kind of spectrum is called an emission spectrum. A constellation is a group of stars named by ancient astronomers. An asterism is a group of stars which is inside a single constellation or a group of stars in several different constellations. Mnemonics are formulas or aids to help in remembering.