Asterism may refer to:
- Asterism (astronomy), a pattern of stars
- Asterism (gemology), an optical phenomenon in gemstones
- Asterism (typography), a moderately rare typographical symbol denoting a break in passages
Asterism (from star), or star stone, is a name applied to the phenomenon of gemstones exhibiting a luminous star-like shape when cut en cabochon. The typical asteria is the star sapphire, generally a bluish-grey corundum, milky or opalescent, with a star of six rays. In red corundum the stellate reflection is less common, and hence the star- ruby occasionally found with the star-sapphire in Sri Lanka is among the most valued of "fancy stones". When the radiation is shown by yellow corundum, the stone is called star- topaz. Cymophane, the chatoyant chrysoberyl known as cat's eye, may also be asteriated. In all these cases the asterism is due to the reflection of light from twin- lamellae or from fine tubular cavities or thin enclosures definitely arranged in the stone. The astrion of Pliny the Elder is believed to have been a moonstone, since it is described as a colourless stone from India having within it the appearance of a star shining with the light of the moon. Star-stones were formerly regarded with much superstition.
Colloquial usage does not draw a sharp distinction between constellation in the sense of an asterism (pattern of stars) and constellation in the sense of an area of the sky surrounding an asterism. The modern system of constellations used in astronomy employs the latter concept. For example, the asterism known as the Big Dipper comprises the seven brightest stars in the International Astronomical Union (IAU) constellation named Ursa Major.
Like constellations, asterisms are in most cases composed of stars which, although visible in the same general area as viewed from Earth, are often located at very different distances from Earth.
Simple shapes composed of a few stars make asterisms easy to identify. Thus they are particularly useful to people who are familiarizing themselves with the night sky.
In typography, an asterism, from the Greek astēr (star), is a rarely used and almost obsolete symbol consisting of three asterisks placed in a triangle. The O3 Coding Club has claimed the asterism, in order to spare it from irrelevance. It is used to "indicate minor breaks in text," call attention to a passage, or to separate sub-chapters in a book. It is Unicode character . In Windows it is possible to use the key combination ALT+8258 to produce the character, but it has very limited support in the default fonts ( Arial Unicode MS / Code2000 / Lucida Sans Unicode / MS Mincho).
Often, this symbol is replaced with three consecutive asterisks (called a dinkus), more than three asterisks, or three or more dots. Otherwise, an extra space between paragraphs is used. An asterism or its analogue may be used in conjunction with the extra space to mark a smaller subdivision than a sub-chapter.
It can also be used to mean 'untitled' or author or title withheld, for example, some editions of Album for the Young by composer Robert Schumann (no.'s 21, 26, and 30). Besides originating from the same word, "the rarely used asteriscus, which Isidore of Seville says 'is put in place of something that has been omitted so as to call attention to the omission'," also resembles the asterism. In meteorology, an asterism in a station model indicates moderate snowfall.
The asterism should not be confused with the similar looking therefore sign——which is composed of three round dots rather than asterisks.
The Collaborative International Dictionary
Asterism \As`ter*ism\, n. [Gr. ?, fr. 'asth`r star; cf. F. ast['e]risme.]
A constellation. [Obs.]
A small cluster of stars.
An asterisk, or mark of reference. [R.]
Three asterisks placed in this manner, [asterism], to direct attention to a particular passage.
(Crystallog.) An optical property of some crystals which exhibit a star-shaped by reflected light, as star sapphire, or by transmitted light, as some mica.
n. 1 (context constellation English) A small group of stars that forms a visible pattern but is not an official constellation. 2 A rarely used typographical symbol (⁂, three asterisks arranged in a triangle), used to call attention to a passage or to separate subchapters in a book. 3 (context mineralogy English) A star-shaped figure exhibited by some crystals by reflected light (as in a star sapphire) or by transmitted light (as in some mica).
Douglas Harper's Etymology Dictionary
1590s, "a constellation, a group of stars," from Greek asterismos "a marking with stars," from aster "star" (see astro-). Any grouping of stars, whether a constellation or not (though in modern use, usually the latter). The "Big Dipper" is an asterism, not a constellation.
n. (mineralogy) a six-rayed star-shaped figure seen in some crystal structures under reflected or transmitted light
(astronomy) a cluster of stars (or a small constellation)
Usage examples of "asterism".
The belief that the stars were living beings, combining with the fancy of an unscientific time, gave rise to the stellar apotheosis of heroes and legendary names, and was the source of those numerous asterisms, out lined groups of stars, which still bedeck the skies and form the landmarks of celestial topography.
He tried to learn them, but they made even less sense than the three-thousand-year-old asterisms of the north.
This most attractive asterism, which has never ceased to fascinate the imagination of Christendom since it was first devoutly described by the early explorers of the South, is but a passing collocation of brilliant stars.