Final answer:
The fluorescence microscope is used to observe a specimen that emits light when illuminated with an ultraviolet light.
Step-by-step explanation:
The microscope used to observe a specimen that emits light when illuminated with an ultraviolet light is the fluorescence microscope. This microscope uses a specific light source to excite fluorescent molecules in the specimen, causing them to emit light of a longer wavelength, which can then be detected and visualized. Fluorescence microscopy is widely used in various fields of research, such as cell biology and immunology, to study specific molecules and cellular processes.