Key Ideas

Refracting Telescopes: Refracting telescopes, or refractors, produce images by bending light rays as they pass through glass lenses.

Reflecting Telescopes: Reflecting telescopes, or reflectors, produce images by reflecting light rays to a focus point from curved mirrors.

Angular Resolution: A telescope’s angular resolution, which indicates ability to see fine details, is limited by two key factors.

Charge-Coupled Devices: Sensitive electronic light detectors called charge-coupled devices (CCDs) are often used at a telescope’s focus to digitally record faint images.

Spectrographs: A spectrograph uses a diffraction grating to form the spectrum of an astronomical object.

Radio Telescopes: Radio telescopes use large reflecting dishes to focus radio waves onto a detector.

Transparency of Earth’s Atmosphere: Earth’s atmosphere absorbs much of the radiation that arrives from space.

Telescopes in Space: For observations at wavelengths to which Earth’s atmosphere is opaque, astronomers depend on telescopes carried above the atmosphere by rockets or spacecraft.