Tuesday, April 30, 2013
Monday, April 29, 2013
Sunday, April 28, 2013
Heiligenschein (German for "aureola" , literally "saint's shine", pronounced [ˈhaɪlɪɡənˌʃaɪn]) is an optical phenomenon which creates a bright spot around the shadow of the viewer's head. It is created when the surface on which the shadow falls has special optical characteristics. Dewy grass is known to exhibit these characteristics, and creates a Heiligenschein. Nearly spherical dew droplets act as lenses to focus the light on the surface beneath them. Some of this light 'backscatters' in the direction of the sunlight as it passes back through the dew droplet. This makes the antisolar point appear the brightest.
The opposition effect creates a similar halo effect, a bright spot of light around the viewer's head when the viewer is looking in the opposite direction of the sun, but is instead caused by shadows being hidden by the objects casting them. When viewing the Heiligenschein, there are no coloured rings around the shadow of the observer, as in the case of a glory.
Saturday, April 27, 2013
A glory is an optical phenomenon, appearing much like an iconic Saint's halo about the head of the observer, produced by light backscattered (a combination of diffraction, reflection and refraction) towards its source by a cloud of uniformly-sized water droplets. The association with a halo is not coincidental, but derivative, though a real glory has multiple colored rings.
Friday, April 26, 2013
Airglow (also called nightglow) is the very weak emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky to never be completely dark (even after the effects of starlight and diffused sunlight from the far side are removed).
Thursday, April 25, 2013
An afterglow is a broad high arch of whitish or rosy light appearing in the sky due to very fine particles of dust suspended in the high regions of the atmosphere. An afterglow may appear above the highest clouds in the hour of deepening twilight, or reflected from the high snowfields in mountain regions long after sunset. The particles produce a scattering effect upon the component parts of white light.
After the eruption of the volcano Krakatoa in 1883, a remarkable series of red sunsets appeared worldwide. These were due to an enormous amount of exceedingly fine dust blown to a great height by the volcano's explosion, and then globally diffused by the high atmospheric currents. Edvard Munch's painting The Scream possibly depicts an afterglow during this period.
Wednesday, April 24, 2013
In gemology, chatoyancy, or chatoyance, is an optical reflectance effect seen in certain gemstones. Coined from the French "œil de chat," meaning "cat's eye," chatoyancy arises either from the fibrous structure of a material, as in tiger eye quartz, or from fibrous inclusions or cavities within the stone, as in cat's eye chrysoberyl. The effect can be likened to the sheen off a spool of silk: The luminous streak of reflected light is always perpendicular to the direction of the fibres. For a gemstone to show this effect best it must be cut en cabochon, with the fibers or fibrous structures parallel to the base of the finished stone. Faceted stones are less likely to show the effect well.
Gem species known for this phenomenon include the aforementioned quartz, chrysoberyl, beryl (especially var. aquamarine), tourmaline, apatite, moonstone and scapolite. Glass optical cable can also display chatoyancy if properly cut, and has become a popular decorative material in a variety of vivid colors.
Tuesday, April 23, 2013
A distinction can be made between two types of asterism:
- Epiasterism, such as that seen in sapphire and most other gems, is the result of a reflection of light on parallel arranged inclusions inside the gemstone.
- Diasterism, such as that seen in rose quartz, is the result of light transmitted through the stone. In order to see this effect, the stone must be illuminated from behind.
Monday, April 22, 2013
Lustre (or luster) is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance.
A range of terms are used to describe lustre. Many terms refer to materials having similar lustres, such as earthy, metallic, greasy, and silky. Similarly, the term vitreous (derived from the Latin for glass, vitrum) refers to a glassy lustre. A list of these terms is given below.
Sunday, April 21, 2013
Saturday, April 20, 2013
An ipse-dixitism or bare assertion is an unsupported or dogmatic assertion; it is a term sometimes used to point out a missing argument.
Someone guilty of perpetrating an ipse-dixitism does not explicitly define it as an axiom, and certainly not as a premise, but often appears presented in syllogistic form, as: "The economy needs more scientists, so expansion of science education will boost the future economy". The proposition rests on an ipse-dixitism unless the speaker gives reasons why "the economy needs more scientists".
Friday, April 19, 2013
Thursday, April 18, 2013
Wednesday, April 17, 2013
Tuesday, April 16, 2013
Monday, April 15, 2013
Sunday, April 14, 2013
Saturday, April 13, 2013
Friday, April 12, 2013
Thursday, April 11, 2013
Wednesday, April 10, 2013
Tuesday, April 9, 2013
Monday, April 8, 2013
Sunday, April 7, 2013
Saturday, April 6, 2013
Friday, April 5, 2013
Wednesday, April 3, 2013
Tuesday, April 2, 2013
- (UK, informal) To obtain (something) for free, particularly by guile or persuasion.
- (UK, informal) More specifically, to obtain confidential information by impersonation or other deception.
- The newspaper is accused of blagging details of Gordon Brown's flat purchase from his solicitors.
- (UK, informal) To beg, to cadge.
- Can I blag a fag?
- (UK, informal) To steal.
- (Polari) To pick up someone.
- (UK, informal, 1960s) To persuade.
- He's blagged his way into many a party.
- (UK, informal, 1940s) To deceive, to perpetrate a hoax on.