What is the primary function of an optical telescope?

The primary function of an optical telescope is to gather and focus light in order to create magnified images of distant objects. This ability to collect and concentrate light is critical for observing faint celestial bodies that are far from Earth, allowing astronomers to study various features of stars, planets, and other astronomical phenomena in much greater detail than would be possible with the naked eye. The design of optical telescopes, whether refractors or reflectors, involves lenses or mirrors that bend or reflect light to form clear images, thus enabling the examination of objects that are billions of light-years away.

The other options touch on important scientific concepts but do not align with the main purpose of an optical telescope. Measuring the speed of light involves different principles and is not the telescope's function; observing chemical reactions in light pertains more to chemistry and photochemistry; analyzing the electromagnetic spectrum is more relevant to spectrophotometers and other instruments designed to study light’s properties across various wavelengths, rather than the primary imaging capability of optical telescopes.