Radioactive elements used in absolute dating

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.

They are unified by thinking of them as "electromagnetic waves," waves of alternating strength in electric and magnetic fields that all move through space at the "speed of light" (called "c") of 300,000 kilometers per second (186,000 miles per second), eight times around the Earth in the tick of a clock.

Shorter-wave photons have increasingly potent effects. Infrared is felt as heat, visual radiation excites the chemistry of the eye, ultraviolet burns, and no one wants to stand in front of an active X-ray machine for long.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.A single gamma ray photon can carry the energy of over a million million million radio photons.Light and its partners can be manipulated in a variety of ways.

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