Snowflake Snowflake viewed in an optical microscope A snowflake is either a single ice crystal or an aggregation of ice crystals which falls through the Earth's atmosphere. They begin as snow crystals which develop when microscopic supercooled cloud droplets freeze. Snowflakes come in a variety of sizes and shapes. Formation Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. The exact details of the sticking mechanism remain controversial. Symmetry A non-aggregated snowflake often exhibits six-fold radial symmetry. Uniqueness Almost all snowflakes are unique Snowflakes form in a wide variety of intricate shapes, leading to the popular expression that "no two are alike". Use as a symbol Snow flake symbol Snowflakes are also often used as symbols representing winter or cold conditions. Gallery A selection of photographs taken by Wilson Bentley (1865–1931): See also References ^ Jump up to: a b William J. Further reading
Sulfur Sulfur occurs naturally as the pure element (native sulfur) and as sulfide and sulfate minerals. Elemental sulfur crystals are commonly sought after by mineral collectors for their distinct, brightly colored polyhedron shapes. Being abundant in native form, sulfur was known in ancient times, mentioned for its uses in ancient India, ancient Greece, China and Egypt. Fumes from burning sulfur were used as fumigants, and sulfur-containing medicinal mixtures were used as balms and antiparasitics. Sulfur is referred to in the Bible as brimstone (burn stone) in English, with this name still used in several nonscientific tomes. It was needed to make the best quality of black gunpowder. In 1777, Antoine Lavoisier helped convince the scientific community that sulfur was a basic element rather than a compound. Elemental sulfur was once extracted from salt domes where it sometimes occurs in nearly pure form, but this method has been obsolete since the late 20th century. Characteristics
Element Element or elements may refer to: Arts Film Elements trilogy, three films by Indian film-maker Deepa Mehta Literature Lower Elements, a fictional underground city in the Artemis Fowl world, created by Eoin Colfer Magazines Element Magazine, a men's lifestyle and fashion digital magazine published in Singapore since 2013 Music Automobiles Honda Element, a car Business Element by Westin, a brand of Starwood Hotels and Resorts WorldwideElement Skateboards, a skateboard manufacturer Chemistry and science Chemical element, a pure substance consisting of one type of atomElectrical element, an abstract part of a circuitHeating element, a device that generates heat by electrical resistanceOrbital elements, the parameters required to uniquely identify a specific orbit of one body around anotherWeather, sometimes referred to as "the elements" Computing Law Mathematics Philosophy Places See also
Sylph Alchemy and literature As alchemy derived from the Swiss German alchemist Paracelsus, alchemists and related movements, such as Rosicrucianism, continued to speak of sylphs in their hermetic literature. The first mainstream discussion of sylphs comes with Alexander Pope. In Rape of the Lock, Pope satirizes French Rosicrucian and alchemical writings when he invents a theory to explain the sylph. In a parody of heroic poetry and the "dark" and "mysterious" literature of pseudo-science, and in particular the sometimes esoterically Classical heroic poetry of the 18th century in England and France, Pope pretends to have a new alchemy, in which the sylph is the mystically, chemically condensed humors of peevish women. Willow, in Terry Brooks' Magic Kingdom of Landover series is a sylph and the wife of protagonist Ben Holiday. Fairy link Sylph has passed into general language as a term for minor spirits, elementals, or faeries of the air. See also
Earth Want to stay on top of all the space news? Follow @universetoday on Twitter Space station above the Earth. The Earth is the third planet from the Sun and the fifth largest of the eight planets in our Solar System. Civilizations throughout the centuries have had different names for our planet as well as various concepts of what it looked like. Earth’s average distance from the Sun is 150 million kilometers. The Earth rotates on its axis in less than 24 hours. Scientists have often tried to discover what makes earth such an ideal place for sustaining life. The air that we breath is mixture of gases. Earth is the densest planet in the Solar System, with an average density of approximately 5520 kg/m 3, which is more than five times the density of water. The Earth is 70% water. Earth is thought to be the only planet in our solar system that has plate tectonics. Our planet has one satellite, which is known simply as the Moon. Tagged as: Earth, planets, Solar System
Corpuscularianism Corpuscularianism is a physical theory that supposed all matter to be composed of minute particles, which became important in the seventeenth century. Among the leading corpuscularians were Pierre Gassendi, Robert Boyle, and John Locke. Corpuscularianism is similar to the theory of atomism, except that where atoms were supposed to be indivisible, corpuscles could in principle be divided. In this manner, for example, it was theorized that mercury could penetrate into metals and modify their inner structure, a step on the way towards the production of gold by transmutation. Corpuscularianism was associated by its leading proponents with the idea that some of the properties that objects appear to have are artifacts of the perceiving mind: "secondary" qualities as distinguished from "primary" qualities. Corpuscularianism stayed a dominant theory for centuries and was blended with alchemy by early scientists such as Robert Boyle and Isaac Newton in the 17th century. Sources
Structure of the Earth Structure of the Earth Assumptions The force exerted by Earth's gravity can be used to calculate its mass, and by estimating the volume of the Earth, its average density can be calculated. Astronomers can also calculate Earth's mass from its orbit and effects on nearby planetary bodies. Structure Earth's radial density distribution according to the preliminary reference earth model (PREM). Earth's gravity according to the preliminary reference earth model (PREM). Comparison to approximations using constant and linear density for Earth's interior. The layering of Earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. Core The average density of Earth is 5,515 kg/m3. The inner core was discovered in 1936 by Inge Lehmann and is generally believed to be composed primarily of iron and some nickel. Mantle World map showing the position of the Moho. Crust See also References
Plasma (physics) Plasma (from Greek πλάσμα, "anything formed") is one of the four fundamental states of matter (the others being solid, liquid, and gas). When air or gas is ionized plasma forms with similar conductive properties to that of metals. Plasma is the most abundant form of matter in the Universe, because most stars are in plasma state. Artist's rendition of the Earth's plasma fountain, showing oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the aurora borealis, where plasma energy pours back into the atmosphere. Plasma is loosely described as an electrically neutral medium of positive and negative particles (i.e. the overall charge of a plasma is roughly zero). Range of plasmas. For plasma to exist, ionization is necessary. Lightning is an example of plasma present at Earth's surface.
Pearl The most valuable pearls occur spontaneously in the wild, but they are extremely rare. These wild pearls are referred to as natural pearls. Cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those that are currently sold. Imitation pearls are also widely sold in inexpensive jewelry, but the quality of their iridescence is usually very poor, and often, artificial pearls are easily distinguished from genuine pearls. Whether wild or cultured, gem quality pearls are almost always nacreous and iridescent, as is the interior of the shell that produces them. Etymology A pearl being extracted from an akoya pearl oyster. A black pearl and a shell of the black-lipped pearl oyster. Definition Almost any shelled mollusk can, by natural processes, produce some kind of "pearl" when an irritating microscopic object becomes trapped within the mollusk's mantle folds, but the great majority of these "pearls" are not valued as gemstones.
Salt (chemistry) There are several varieties of salts. Salts that hydrolyze to produce hydroxide ions when dissolved in water are basic salts, whilst those that hydrolyze to produce hydronium ions in water are acidic salts. Neutral salts are those that are neither acid nor basic salts. Usually, non-dissolved salts at standard temperature and pressure are solid, but there are exceptions (see Molten salts and ionic liquids). Potassium dichromate, a bright orange salt used as a pigment Salts exist in many different colors, for example: Most minerals and inorganic pigments, as well as many synthetic organic dyes, are salts. Solid salts do not conduct electricity. The name of a salt starts with the name of the cation (e.g., sodium or ammonium) followed by the name of the anion (e.g., chloride or acetate). Common salt-forming cations include: Common salt-forming anions (parent acids in parentheses where available) include: Solid lead(II) sulfate (PbSO4) Salts are formed by a chemical reaction between: