Saturn is the sixth planet from the Sun and the second biggest. Saturn has been identified from the time when prehistoric times. Galileo was the first to analysis it with a telescope in 1610; he noted its odd look but was confused by it. Early observations of Saturn were complex by the fact that the Earth passes through the plane of Saturn's rings all few years as Saturn moves in its orbit. A low resolution image of Saturn therefore changes considerably. It was not in anticipation of 1659 that Christian Huygens properly inferred the geometry of the rings. Saturn's rings remained exclusive in the known solar system until 1977 when extremely faint rings were discovered around Uranus.
Saturn is clearly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters differ by almost 10% (120,536 km vs. 108,728 km). This is the end result of its rapid rotary motion and fluid state. The other gas planets are also oblate, but not so a lot so. Saturn's rings are very thin: though they're 250,000 km or more in thickness they're less than one kilometer thick. In spite of their impressive appearance, there's actually very little material in the rings -- if the rings were compressed into a single body it would be no more than 100 km across.
Saturn's outermost ring, the F-ring, is a difficult structure made up of number of smaller rings along which "knots" are visible. Scientists guess that the knots may be clumps of ring material, or mini moons. The odd braided appearance visible in the Voyager 1 images (right) is not visible in the Voyager 2 images perhaps for the reason that Voyager 2 imaged regions where the part rings are generally parallel. They are well-known in the Cassini images which as well show some as yet unexplained wispy spiral structures. The source of the rings of Saturn (and the other Jovian planets) is unidentified. Though they may have had rings since their formation, the ring systems are not firm and must be regenerated by continuing processes, perhaps the breakup of bigger satellites. The present set of rings may be only a few hundred million years old.
Sunday, October 28, 2007
Tuesday, October 16, 2007
Asia
Asia is the world's biggest and most populous continent. It covers 8.6% of the Earth's total surface area (or 29.4% of its land area) and, with almost 4 billion people, it contains more than 60% of the world's present human population.
Chiefly in the eastern and northern hemispheres, Asia is conventionally defined as part of the landmass of Africa-Eurasia – with the western portion of the latter occupied by Europe – lying east of the Suez Canal, east of the Ural Mountains, and south of the Caucasus Mountains and the Caspian and Black Seas. It is surrounded to the east by the Pacific Ocean, to the south by the Indian Ocean, and to the north by the Arctic Ocean.
Given its size and diversity, Asia – a toponym dating back to classical antiquity – is more a cultural concept incorporating a number of regions and peoples than a homogeneous, physical entity.
Chiefly in the eastern and northern hemispheres, Asia is conventionally defined as part of the landmass of Africa-Eurasia – with the western portion of the latter occupied by Europe – lying east of the Suez Canal, east of the Ural Mountains, and south of the Caucasus Mountains and the Caspian and Black Seas. It is surrounded to the east by the Pacific Ocean, to the south by the Indian Ocean, and to the north by the Arctic Ocean.
Given its size and diversity, Asia – a toponym dating back to classical antiquity – is more a cultural concept incorporating a number of regions and peoples than a homogeneous, physical entity.
Monday, October 08, 2007
microcomputer
A microcomputer is mainly often taken to mean a computer with a microprocessor (µP) as its CPU. Another general characteristic of these computers is that they take up physically small amounts of space.Desktop computers, video game consoles, laptop computers, tablet PCs, and a lot of handheld devices may all be considered examples of microcomputers.Most microcomputers serve only a single user at a time, but some, in the form of PCs and workstations running e.g. a UNIX(-like) operating system, may cater to a number of users concurrently. The µP does the majority of the job of calculating on and manipulating data that all computers do.
Subscribe to:
Posts (Atom)