The visible light spectrum is the portion of the electromagnetic spectrum that is visible to the human eye and is commonly
called light. A typical human eye will respond to wavelengths from about 390 to 750 nm.
Spectroscopy is the study of objects based on the spectrum of color they emit or absorb. Spectroscopy is an important investigative tool in astronomy where scientists use it to analyze the properties of distant objects.
Typically, astronomical spectroscopy uses high-dispersion diffraction gratings to observe spectra at very high spectral resolutions.
Helium was first detected by analysis of the spectrum of the sun. Chemical elements can be detected in astronomical objects by emission lines and absorption lines.
The shifting of spectral lines can be used to measure the
(red shift or blue shift) of distant objects and from this shift, the
relative velocity toward or away from the observer can be determined.