Q:  What is the equivalent width of this absorption line?



            The blue area is a very rough triangle with
                  width = 2.5 Angstroms and depth 10,000 units * Angstroms
                  so it has area 

                        area   =  (1/2) * (base) * (height)

                               =  (1/2) * (2.5 Ang) * (10,000 units)

                               =  12,500 Angstrom*units.

            Since the height of the brown rectangle is about
                  40,000 units, its width must be

                                   12,500 Angstrom*units
                        width  =  ----------------------
                                   40,000 units


                               =   0.31  Angstroms