The electromagnetic spectrum includes light and ranges from ultraviolet to infrared. When light passes through a material, some is absorbed or emitted. A spectroscope shows a linear spectrum of brightly colored emission or dark absorption lines. A diffraction grating separates light into its different wavelengths, creating a continuous spectrum. There are two types of line spectrum: emission and absorption. Niels Bohr developed the Bohr model to explain the atomic spectrum. Spectroscopy is used to analyze the unique line spectrum of elements and determine their composition, including in stars.
The electromagnetic spectrum, of which light is a fraction, is a continuous distribution of wavelengths ranging from ultraviolet to infrared. When electromagnetic radiation in the form of light passes through a material, some part of it is either absorbed or emitted by the medium. When you look at this light through a spectroscope, those parts appear as a linear spectrum: brightly colored emission lines against a dark background, or dark absorption lines against a brightly colored background.
When white light passes through a diffraction grating, a continuous spectrum of light appears. The diffraction grating separates light into its different wavelengths, from violet to red, in the visible range. This continuous spectrum is emitted by incandescent solids, liquids and gases under high pressure. The two best known examples of this are white light through a prism and through water droplets, which creates a rainbow.
There are two types of line spectrum: an emission spectrum and an absorption spectrum. The former is also called a bright line spectrum and consists of a few brightly colored lines against a dark background. Each line represents a unique wavelength and the whole thing is unique to that particular element. These lines are emitted when a low pressure gas is brought into contact with an electrical discharge.
A dark line spectrum, or absorption spectrum, is just the opposite: instead of bright lines at each wavelength against a dark background, an absorption spectrum has dark lines at the corresponding wavelengths against a continuous background. This result is the main goal of absorption spectroscopy and is created by passing light through a gas of the element to be analyzed.
Physicist Niels Bohr introduced his idea in 1913 of why the atomic spectrum has the characteristics and properties it does. To do this, Bohr developed his own model of the atom, now called the Bohr model. It assumes that electrons can exist only in discrete orbits around the nucleus and that only certain orbits are stable, meaning that the electron does not emit radiation. Radiation is emitted, however, as the electron moves from a higher-energy orbit to a lower-energy orbit.
Spectroscopy is the analysis of this phenomenon using a machine called a spectroscope. No two elements emit or absorb exactly the same line spectrum, so these observations can be used to determine the elements in a sample. As a result, astronomers have begun turning their spectroscopes to stars in an effort to determine their composition and that of any interstellar medium between a particular star and Earth.
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