Astronomical spectroscopy uses light to study celestial objects' composition, motion, and properties.Astronomical spectroscopy is the technique of dispersing light from celestial objects into its component wavelengths, revealing a wealth of information that is invisible to the naked eye. Every element and molecule leaves a unique pattern of absorption or emission lines in a spectrum, allowing astronomers to determine the chemical composition of stars, galaxies, and nebulae. The Doppler shift of these lines reveals how fast objects are moving toward or away from us, and their broadening can indicate temperature, pressure, and magnetic fields.
The foundations were laid in the 19th century by Joseph von Fraunhofer, who mapped dark lines in the solar spectrum, and by Gustav Kirchhoff and Robert Bunsen, who showed that each element has a unique spectral signature. The first stellar spectra were obtained in the 1860s.
Light from a telescope is passed through a spectrograph, which uses a prism or diffraction grating to spread the light into a spectrum. The resulting spectrum is recorded on a CCD detector. By comparing the observed wavelengths of known spectral lines with laboratory values, astronomers can measure redshifts, chemical abundances, and even the presence of magnetic fields through the Zeeman effect.
Essential for measuring the expansion of the universe (via redshift), finding exoplanets (via radial velocity), and classifying stars by their spectral type.
The element helium was discovered in 1868 in the spectrum of the Sun before it was ever found on Earth.
| j_n | variable | Spherical Bessel function of order n — spherical bessel function |
| x | variable | Radial argument (often kr) — dimensionless argument |
| J_{n+1/2} | variable | Ordinary Bessel function of half-integer order — bessel function |
