Astronomical Detectors & Spectrographs: Foundations

An imaging detector contains pixels with finite quantum efficiency, read noise, dark current, full-well capacity, and gain. A spectrograph commonly includes an entrance slit or fiber, collimating optics, a prism or diffraction grating, camera optics, and a detector.

Photons create charge in a semiconductor detector, and electronics measure that charge after an exposure. In a spectrograph, wavelength-dependent diffraction sends different wavelengths to different detector positions, turning one source into a spectrum.

Calibration frames measure detector bias, dark current, pixel sensitivity, and wavelength mapping. Laboratory lamps with known spectral lines establish the relationship between detector position and wavelength.

Astronomical detectors convert incoming photons into countable signals, while spectrographs distribute those photons by wavelength before detection. A modern observation is therefore a chain: telescope throughput, filters or dispersers, detector quantum efficiency, electronic readout, and calibration. Knowing the detector is as important as knowing the telescope because sensitivity, dynamic range, noise, pixel scale, and wavelength response determine which physical signals survive into the data.