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Please do not edit this page directly. Instead, use one of the "Edit" links on the bottom right of the corresponding section. This will ensure that you edit the correct page for your changes to appear on Portal:Physics in the correct week.
January
editIn mid-August 2010 ESO Photo Ambassador Yuri Beletsky snapped this photo at ESO’s Paranal Observatory, Chile. A group of astronomers were observing the centre of the Milky Way using the laser guide star facility at Yepun, one of the four Unit Telescopes of the Very Large Telescope (VLT).
- Yepun’s laser beam crosses the southern sky and creates an artificial star at an altitude of 90 km high in the Earth's mesosphere. The Laser Guide Star (LGS) is part of the VLT’s adaptive optics system and is used as a reference to correct the blurring effect of the atmosphere on images. The colour of the laser is precisely tuned to energise a layer of sodium atoms found in one of the upper layers of the atmosphere — one can recognise the familiar colour of sodium street lamps in the colour of the laser. This layer of sodium atoms is thought to be a leftover from meteorites entering the Earth’s atmosphere. When excited by the light from the laser, the atoms start glowing, forming a small bright spot that can be used as an artificial reference star for the adaptive optics. Using this technique, astronomers can obtain sharper observations. For example, when looking towards the centre of our Milky Way, researchers can better monitor the galactic core, where a central supermassive black hole, surrounded by closely orbiting stars, is swallowing gas and dust.
- The photo, which was chosen as Astronomy Picture of the Day in September 2010 and the 2010 Wikimedia Picture of the Year, was taken with a wide-angle lens and covers about 180 degrees of the sky.
February
editDifference between classical and modern physics
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While physics aims to discover universal laws, its theories lie in explicit domains of applicability. Loosely speaking, the laws of classical physics accurately describe systems whose important length scales are greater than the atomic scale and whose motions are much slower than the speed of light. Outside of this domain, observations do not match their predictions. Albert Einstein contributed the framework of special relativity, which replaced notions of absolute time and space with spacetime and allowed an accurate description of systems whose components have speeds approaching the speed of light. Max Planck, Erwin Schrödinger, and others introduced quantum mechanics, a probabilistic notion of particles and interactions that allowed an accurate description of atomic and subatomic scales. Later, quantum field theory unified quantum mechanics and special relativity. General relativity allowed for a dynamical, curved spacetime, with which highly massive systems and the large-scale structure of the universe can be well-described. General relativity has not yet been unified with the other fundamental descriptions; several candidate theories of quantum gravity are being developed.
March
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Plasma (from Ancient Greek πλάσμα (plásma) 'moldable substance') is one of four fundamental states of matter (the other three being solid, liquid, and gas) characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. It is the most abundant form of ordinary matter in the universe, mostly in stars (including the Sun), but also dominating the rarefied intracluster medium and intergalactic medium. Plasma can be artificially generated, for example, by heating a neutral gas or subjecting it to a strong electromagnetic field.
Depending on temperature and density, a certain number of neutral particles may also be present, in which case plasma is called partially ionized. Neon signs and lightning are examples of partially ionized plasmas. Unlike the phase transitions between the other three states of matter, the transition to plasma is not well defined and is a matter of interpretation and context. Whether a given degree of ionization suffices to call a substance "plasma" depends on the specific phenomenon being considered. (Full article...)
April
editThe Standard Model of elementary particles
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May
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June
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See: Introduction to general relativity
General relativity is a theory of gravitation that was developed by Albert Einstein between 1907 and 1915. According to general relativity, the observed gravitational effect between masses results from their warping of spacetime. Experiments and observations show that Einstein's description of gravitation accounts for several effects that are unexplained by Newton's law, such as minute anomalies in the orbits of Mercury and other planets. General relativity also predicts novel effects of gravity, such as gravitational waves, gravitational lensing and an effect of gravity on time known as gravitational time dilation. Many of these predictions have been confirmed by experiment, while others are the subject of ongoing research.
July
editThe age of the Earth is 4.54 ± 0.05 billion years (4.54 × 109 years ± 1%).[1][2][3] This age is based on evidence from radiometric age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples. Following the scientific revolution and the development of radiometric age dating, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old.[4]
Studies of strata, the layering of rocks and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer
August
editJupiter as seen by Voyager 1 probe with a special filter.
Once per Jovian day, which is approximately 10 hours, during early 1979, Voyager 1 transmitted images of Jupiter. These pictures were taken from January 6th to February 3rd. Also, Voyager 1 flew from a distance of 58 million kilometers (36 million miles) from Jupiter, to a closer distance of 31 million kilometers (a little over 19 million miles), as the picture shows movement from a farther distance to a closer approach. The small, round, dark spots appearing in some frames are the shadows cast by Jupiter's moons, which pass between Jupiter and the Sun.
September
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October
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November
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- Refraction of light (which is described by w:en:Optics)
- A laser
- A hot air balloon
- A spintop (whose movement is described by classical mechanics)
- The effects of an inelastic collision
- Atomic orbitals of hydrogen atom (which are described by w:en:quantum mechanics)
- An atomic bomb exploding
- Lightning (which is an electrical phenomenon)
- Galaxies (photo made by the Hubble Space Telescope)
December
edit - Refraction of light (which is described by w:en:Optics)
- A laser
- A hot air balloon
- A spintop (whose movement is described by classical mechanics)
- The effects of an inelastic collision
- Atomic orbitals of hydrogen atom (which are described by w:en:quantum mechanics)
- An atomic bomb exploding
- Lightning (which is an electrical phenomenon)
- Galaxies (photo made by the Hubble Space Telescope)
References
edit- ^ "Age of the Earth". U.S. Geological Survey. 1997. Archived from the original on 23 December 2005. Retrieved 2006-01-10.
- ^ Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Special Publications, Geological Society of London. 190 (1): 205–221. Bibcode:2001GSLSP.190..205D. doi:10.1144/GSL.SP.2001.190.01.14.
- ^ Manhesa, Gérard; Allègre, Claude J.; Dupréa, Bernard & Hamelin, Bruno (1980). "Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics". Earth and Planetary Science Letters. 47 (3): 370–382. Bibcode:1980E&PSL..47..370M. doi:10.1016/0012-821X(80)90024-2.[verification needed]
- ^ Boltwood, B. B. (1907). "On the ultimate disintegration products of the radio-active elements. Part II. The disintegration products of uranium". American Journal of Science. 23 (134): 77–88. doi:10.2475/ajs.s4-23.134.78.
For the abstract, see: Chemical Abstracts Service, American Chemical Society (1907). Chemical Abstracts. New York, London: American Chemical Society. p. 817. Retrieved 2008-12-19.