The ability of a telescope to collect light from an astronomical source. The light-gathering power is directly related to the area of the primary mirror or lens.

The amount of light collected by a mirror or lens. Light-gathering power is determined by the primary objective's surface area. A doubling of aperture produces a four-fold increase in light-gathering power.

A measure of a telescope's ability to collect light. Light gathering power is proportional to the telescope's lens or mirror surface area. Astronomers enjoy observing through large aperture telescopes because they may see faint, distant objects and detail of nearby objects.