Hubble’s primary mirror has a diameter of 2.4 meters. This large, precisely polished mirror collects incoming light and reflects it to Hubble’s secondary mirror, which directs the focused beam toward the telescope’s scientific instruments.
Hubble is a reflecting telescope, so its mirror—not a glass lens—forms the main light-gathering surface. The 2.4-meter aperture gives Hubble substantial collecting power and excellent resolution, while its position above Earth’s atmosphere prevents atmospheric turbulence from blurring images and blocks much ultraviolet light from reaching the ground.
The mirror’s size is sometimes confused with Hubble’s overall dimensions. The observatory is about 13.2 meters long, but its primary mirror is only 2.4 meters across. Another famous detail is that the mirror was polished to the wrong shape, producing spherical aberration. Astronauts corrected the problem during the 1993 servicing mission by installing corrective optics and instruments.