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Compact Cosmos

32 33 SHIFTINGSPECTRA expanding space One puzzle facing astronomers has beento findthe composition of distant objects. Spectroscopy uses the unique fingerprint frequencies at which atoms and molecules emit or absorb light. Splitting the light received from an object into a spectrum reveals these frequencies as spectral lines, which can then be analyzed to determine the chemical ingredients. Light can also be used to estimate speed. Approaching objects appear blueshifted as light waves bunch up toward the blue end of the spectrum. Conversely as an object recedes the light waves are stretched,to become redshifted. This Dppler effect is used to judge velocity by measuring how far the distinctive patterns of spectral lines have been moved along the spectrum. Observations show that faint,distant galaxies become increasingly redshifted,suggesting that the farther away an object is,the faster it is racing away from us. The implication of this cosmological redshift is that the whole universe is expanding. Hubbles Lawcharts a relationship between a galaxys brightness and redshift,indicating the immense distances involved. The highest redshifts found have belonged to quasars billions of lightyears away, suggesting they are either hurtling off at a significant fraction of light speed or are closer and behaving very weirdly.
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