In physics, aredshift is an increase in thewavelength, or equivalently, a decrease in thefrequency andphoton energy, ofelectromagnetic radiation (such aslight). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift. The terms derive from the colours red and blue, which form the extremes of thevisible-light spectrum. Three forms of redshift occur inastronomy andcosmology:Doppler redshifts due to the relative motions of radiation sources,gravitational redshift as radiation escapes from gravitational potentials, and cosmological redshifts caused by theuniverse expanding. Automated astronomical redshift surveys are an important tool for learning about the large scale structure of the universe. Examples of strong redshifting are agamma ray perceived as anX-ray, or initially visible light perceived asradio waves. The initial heat from theBig Bang has redshifted far down to become thecosmic microwave background. (Full article...)
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Pachygrapsus marmoratus, also known as the marbled crab, is a species in the familyGrapsidae, the marsh crabs. The species is found in southern Europe and northern Africa, in the waters of the Black Sea, the Mediterranean Sea, and parts of the Atlantic Ocean. It is a dark violet-brown crab, with yellow marbling, and with a body up to 36 millimetres (1.4 inches) long. Asemiaquatic omnivore, it feeds onalgae and various animals includingmussels andlimpets. ThisP. marmoratus crab was photographed near the shore ofButrint Lagoon inButrint National Park, southern Albania, near the coast of theIonian Sea. The picture has beenfocus-stacked from 12 separate images. Photograph credit:Charles J. Sharp Recently featured: |
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