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Spectral Analysis


As recently as the 19th century, many people thought that it would be impossible to determine the chemical composition of the stars. Since then, astrophysicists have proved them wrong -- using spectroscopy.

The word 'spectrum' (the plural of which is 'spectra') is used today to mean 'a display of electromagnetic radiation as a function of wavelength.' Spectrum used to mean 'phantom' or 'apparition', but Isaac Newton introduced a new meaning in 1671, when he reported his experiment of decomposing the white sunlight into colors using a prism. Several related words, such as 'spectroscopy' (the study of spectra) and 'spectrograph', have since been introduced into the English language.

You can be a spectroscopist (a person who studies spectra), too! When you see a rainbow, observe it carefully. Or use a prism on a beam of sunlight to project a band of colors onto a screen or a wall. It will probably look to your eyes like the change of colors is gradual, and the change in intensity of light of different colors is also gradual. We use the word 'continuum' to describe spectra that change gradually like this.

There are also discrete features, called 'emission lines' or 'absorption lines' depending on whether they are brighter or fainter than the neighboring continuum. You can use a prism on candlelight or some special light bulbs to see such spectral lines.

* How do you make a spectrograph?
* What do spectra tell us?
* What's so special about X-ray and gamma-ray spectra?
    * Use Hera to try your hand at analyzing spectra with modern data.

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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