How does an optical telescope collect and focus light from distant objects?

Optical telescopes collect and focus light from distant objects to make them appear brighter and more detailed than they do to the naked eye. The primary difference between human vision and a telescope is the size of the light-gathering aperture, which allows telescopes to capture far more light from faint celestial sources.1

There are two main types of optical telescopes, categorized by how they focus this light:

• Refracting telescopes (refractors): These use an objective lens to collect and bend (refract) light. As light passes through the glass, it converges at a focal point. An eyepiece lens is then placed behind this focal plane to magnify the image for the observer.2
• Reflecting telescopes (reflectors): Most modern telescopes are reflectors, which use large, curved mirrors to collect and redirect light toward scientific instruments or an eyepiece. By using mirrors instead of lenses, these telescopes avoid chromatic aberration, a distortion where different colors of light focus at different points.12

The power of a telescope is largely determined by its aperture; a larger diameter allows for greater light-gathering capacity and higher resolving power, enabling the observation of distant galaxies and faint stars.13