Absolute and relative dating examples

In the modern spectrograph, light is sent from the telescope onto a "collimator," a curved mirror that straightens the converging beam.

The collimator sends the beam to a reflecting grating that makes a spectrum, the colored light then focused by a camera onto a detector, usually a "charge-coupled device," or "CCD," that records the spectra digitally.

Turned to the sky and attached to a detector, the lens becomes an astronomical telescope.

(A curved mirror can create a similar image by reflection.) The speed of an electromagnetic wave in a medium depends on its wavelength.

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Spectra can also be created by the interference of light waves, the phenomenon that makes the brightly colored patterns seen reflected from a compact audio disc and the halos often observed next to a bright, partly clouded Moon.Spectra are commonly seen reproduced either photographically or graphically.Electromagnetic energy cannot be separated from matter.This site, closely coupled to The Natures of the Stars and The Hertzsprung- Russell (HR) Diagram, provides an introduction to the spectra of stars and allied celestial objects.Here we examine the principal way in which astronomers have learned so much about the stars. Pass sunlight through a triangular prism or bounce it off the finely grooved surface of a compact audio disk and see it break merrily into a band of pure sparkling color, its "spectrum," familiar in the colors of a rainbow, in light glittering from newly fallen snow, in the rings and haloes around a partly- clouded Sun and Moon, in the flash of a cut diamond, and in so many other facets of nature.

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