Visible-light astronomy

Visible-light astronomy studies celestial objects and phenomena through electromagnetic radiation detectable by the human eye, from about 400 to 700 nanometers.

Optical telescope: An instrument that collects and focuses visible or near-visible electromagnetic radiation to study distant objects. Its mirrors or lenses gather faint celestial light and form images for analysis.
Stellar classification: The organization of stars into types based primarily on their spectra and surface temperatures. Visible stellar spectra provide the absorption features used to classify many stars.
Radio astronomy: The study of celestial objects through radio-frequency electromagnetic radiation. Radio waves reveal emission and structures that visible images may not show.
Galileo Galilei: An Italian astronomer and physicist who made pioneering telescopic observations in the early seventeenth century. His telescopic observations of the Moon, Jupiter, and Venus transformed optical astronomy.
Electromagnetic spectrum: The full range of electromagnetic radiation, ordered by frequency, wavelength, or photon energy. Visible light occupies a narrow band within this broader range of radiation.
Astronomical seeing: The blurring and distortion of astronomical images caused by turbulence in Earth's atmosphere. Atmospheric turbulence limits the sharpness of ground-based visible observations.
Hertzsprung–Russell diagram: A plot relating stars' luminosities or absolute magnitudes to their surface temperatures or spectral types. Visible magnitudes and colors place stars on a diagram that tracks stellar evolution.
Infrared astronomy: The study of celestial objects through infrared electromagnetic radiation. Infrared observations penetrate dust and detect cooler objects that emit little visible light.
Johannes Kepler: A German astronomer who formulated laws describing the elliptical orbits of planets. His account of planetary motion helped establish a mathematical framework for observations.
Visible spectrum: The range of electromagnetic wavelengths detectable by the human visual system. It defines the radiation band examined in visible-light astronomy.

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Wide-field Infrared Survey ExplorerCompared with: WISE revealed cool or dust-hidden sources that visible-light observations can miss.