- published: 25 Oct 2009
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A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. Butterflies comprise the true butterflies (superfamily Papilionoidea), the skippers (superfamily Hesperioidea) and the moth-butterflies (superfamily Hedyloidea). All the many other families within the Lepidoptera are referred to as moths. The earliest known butterfly fossils date to the mid Eocene epoch, between 40–50 million years ago.
Butterflies exhibit polymorphism, mimicry and aposematism. Some, like the Monarch, will migrate over long distances. Some butterflies have evolved symbiotic and parasitic relationships with social insects such as ants. Some species are pests because in their larval stages they can damage domestic crops or trees; however, some species are agents of pollination of some plants, and caterpillars of a few butterflies (e.g., Harvesters) eat harmful insects. Culturally, butterflies are a popular motif in the visual and literary arts.
A dress (also known as a frock or a gown) is a garment consisting of a skirt with an attached bodice (or a matching bodice giving the effect of a one-piece garment). In Western culture, dresses are usually considered to be items of women's and girls' apparel.
The hemline of dresses can be as high as the upper thigh or as low as the ground, depending on the whims of fashion and the modesty or personal taste of the wearer.
Dresses increased dramatically to the hoopskirt and crinoline-supported styles of the 1860s; then fullness was draped and drawn to the back. Dresses had a "day" bodice with a high neckline and long sleeves, and an "evening" bodice with a low neckline (decollete) and very short sleeves.
Throughout this period, the length of fashionable dresses varied only slightly, between ankle-length and floor-sweeping.
In Europe and America, dresses are worn by females of all ages as an alternative to a separate skirt and blouse or trousers.
Dresses however can be cooler and less confining than many trouser styles, and they are very popular for special occasions such as proms or weddings.
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible from Earth during the night, when they are not obscured by atmospheric phenomena, appearing as a multitude of fixed luminous points because of their immense distance. Historically, the most prominent stars on the celestial sphere were grouped together into constellations and asterisms, and the brightest stars gained proper names. Extensive catalogues of stars have been assembled by astronomers, which provide standardized star designations.
For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen in its core releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium were created by stars, either via stellar nucleosynthesis during their lifetimes or by supernova nucleosynthesis when stars explode. Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history, including diameter, rotation, movement and temperature. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung–Russell diagram (H–R diagram), allows the age and evolutionary state of a star to be determined.