A comet is a small body orbiting the sun on an elliptical path with a long tail of dust and ice.
Some comets are only visible by the aid of the telescope, while others can be seen by the naked eye. In the latter case they usually appear like stars accompanied with a train of light, sometimes short and sometimes extending over half the sky, mostly single and more or less curved, but sometimes forked. In a comet which appeared in 1744 the train was divided into several branches, spreading out from the head like a fan. The train is not stationary relatively to the head, but is subject to remarkable movements. The direction in which it points is always opposite to the sun, and as the , comet passes its perihelion the train changes its apparent position with extraordinary velocity. The head of the comet is itself of different degrees of luminosity, there being usually a central core, called the nucleus, of greater brilliancy than the surrounding envelope, called the coma.
Comets were long regarded as supernatural objects, and usually as portents of impending calamity. Tycho Brahe was the first who expressed a rational opinion on the subject, coming to the conclusion that the comet of 1577 was a heavenly body at a greater distance from the earth than that of the moon. The general law of the motion of bodies, as well as his own observations on the comet of 1680, led Isaac Newton to conclude that the orbits of the comets must, like those of the planets, be ellipses, having the sun in one focus, but far more eccentric; and having their aphelions, or greater distances from the sun, far remote in the regions of space.
This idea was taken up by Halley, who collated the observations which had been made of all the twenty-four comets of which notice had been taken previous to 1680. The results were very interesting. With but few exceptions the comets had passed within less than the earth's shortest distance from the sun, some of them within less than one-third of it, and the average about one-half. Out of the number, too, nearly two-thirds had had their motions retrograde, or moved in the opposite direction to the planets. While Halley was engaged on these comparisons and deductions the comet of 1682 made its appearance, and he found that there was a wonderful resemblance between it and three other comets that he found recorded - the comets of 1456, of 1531, and of 1607. The times of the appearance of these comets had been at very nearly regular intervals, the average period being between seventy-five and seventy-six years. Their distances from the sun, when in perihelion, or when nearest to that luminary, had been nearly the same, being nearly six-tenths of that of the earth, and not varying more than one-sixtieth from each other.
The inclination of their orbits to that of the earth had also been nearly the same, between 17 degrees and 18 degrees; and their motions had all been retrograde. Putting these facts together, Halley concluded that the comets of 1456, 1531,1607, and 1682 were reappearances of one and the same comet, which revolved in an elliptic orbit round the sun, performing its circuit in a period varying from a little more than seventy-six years to a little less than seventy-five; or having, as far as the observations had been carried, a variation of about fifteen months in the absolute duration of its year, measured according to that of the earth. For this variation in the time of its revolution Halley accounted upon the supposition that the form of its orbit had been altered by the attraction of the remote planets Jupiter and Saturn as it passed near to them; and thence he concluded that the period of its next appearance would be lengthened, but that it would certainly reappear in 1758 or early in 1759. As the time of its expected reappearance approached, Clairaut calculated that it would be retarded 100 days by the attraction of Saturn, and 518 by that of Jupiter, so that it would not come to the perihelion, or point of its orbit nearest the 500 sun, until the 13th of April, 1759.
It actually reached its perihelion on the 13th of March, 1759, being thirty days earlier than he had calculated. Along with the period of this comet and its perihelion distance, the magnitude and form of its path were also calculated. Estimating the mean distance of the earth from the sun at 95,000,000 miles (the number which was at that time considered as the true one), the mean distance of the comet was calculated to be 1,705,250,000 miles; its greatest distance from the sun, 3,355,400,000; its least distance, 55,100,000; and the transverse or largest diameter of its orbit, 3,410,500,000. This comet, therefore, is a body belonging to the solar system, and quite beyond the attraction of any body which does not belong to that system; and as this is determined of one comet, analogy points it out as being the case with them all. In 1835 it again returned, being first seen at Rome, on August the 5th, and from that time continued to be observed until the end of the year in Europe, and through a great part of spring 1836 in the southern hemisphere.
The comet denominated Encke's comet, which has made repeated appearances, was first observed in 1818, and was identified with a comet observed in 1786, also with a comet discovered in 1795 by Miss Herschel in the constellation Cygnus, and with another seen in 1805. Its orbit is an ellipse of comparatively small dimensions, wholly within the orbit of Jupiter; its period is 1260 days, or about three years and three-tenths. It has been frequently observed since.
Another comet, the history of which is of the utmost importance in the latest theories regarding the connection of these bodies and the periodic showers of shooting-stars, is one known as Biela's comet, discovered in 1826. It revolved about the sun in about 6.75 years, and was identified as the same comet which was observed in 1772 and in 1806. Its returns were noted in 1832, 1839, and 1845. In 1846 it divided into two, returned double in 1852, but has not since been seen, the Supposition being that it has been dissipated, and that it was represented by a great shower of meteors that were seen in November 1872. One of the most remarkable comets of recent times was that known as Donati's, discovered by Dr. Donati of Florence in 1858. It was very brilliant in England in the autumn of that year, and on the 18th of October was near coming into collision with Venus, The year 1881 was remarkable for the number of comets recorded. During that year no fewer than seven comets, including the well-known short-period comet Encke's, were observed. Research Comet
The Ptolemaic system was a system of astronomy set forth by the Egyptian astronomer Clausius Ptolemaeus during the 11th century. By the Ptolemaic system the earth is fixed in the centre of the universe and the heaves revolve around the earth from east to west, carrying with them the sun, planets and fixed stars in their respective spheres. The system says that the Moon is next above the earth, then Mercury, then Venus; the Sun is next then Mars, and then after MarsJupiter and Saturn, beyond Saturn are two crystalline spheres.
It was the nonsense of the Ptolemaic system that Copernicus proved wrong and was so persecuted for until his system was adopted in the sixteenth century. Research Ptolemaic System
The week is the period of seven days now universally adopted. It is of Hebrew or Chaldean origin and is generally regarded as a memorial of the creation of the world according to the Mosaic account. Dion Cassius attributes the invention of the week to the Egyptians. The Ptolemaic arrangement of the heavenly bodies, according to their distances from the earth, is Saturn (the most distant), Jupiter, Mars, the sun, Venus, Mercury and the Moon; and it was a principle of the ancient astrology that these bodies presided in this succession over the hours of the day. If the first hour be assigned to Saturn, the twenty-fifth or first hour of the next day, will fall to the sun; the forty-ninth, or first hour of the second day will fall to the moon and so on. From the names of the planets have been formed the modern names - Saturday (Saturn), Sunday (Sun), Monday (Moon), Tuesday (Tiu, the Saxonequivalent of Mars), Wednesday (Woden the Norseequivalent of Mercury), Thursday (Thor the Norseequivalent of Jupiter) and Friday (Frygga the Norseequivalent of Venus). Research Week
The zodiac was the name given by the ancient Greeks to the heavens. It was an imaginary belt in the celestial sphere, extending about 80 degrees on either side of the ecliptic, the apparent path of the Sun among the stars. The width of the zodiac was determined originally so as to include the orbits of the Sun and Moon and of the five planets (Mercury, Venus, Mars, Jupiter, and Saturn) that were known to the people of ancient times.
The zodiac is divided into 12 sections of 300 degrees each, which are called the signs of the zodiac. Starting with the vernalequinox and then proceeding eastward along the ecliptic, each of the divisions is named for the constellation situated within its limits in the second century BC. The names of the zodiacal signs are Aries, the Ram; Taurus, the Bull; Gemini, the Twins; Cancer, the Crab; Leo, the Lion; Virgo, the Virgin; Libra, the Balance; Scorpio, the Scorpion; Sagittarius, the Archer; Capricorn, the Goat; Aquarius, the Water Bearer; and Pisces, the Fish. Because of the precession of the equinoxes about the ecliptic, a 26,000-year cycle, the first point of Aries retrogrades about 10 degrees in 70 years, so that the sign Aries today lies in the constellationPisces. In about 24,000 years, when the retrogression will have completed the entirecircuit of 3600, the zodiacal signs and constellations will again coincide.
It is believed that the zodiacal signs originated in Mesopotamia as early as 2000 BC . The Greeks adopted the symbols from the Babylonians and passed them on to the other ancient civilisations. The Egyptians assigned other names and symbols to the zodiacal divisions. The Chinese also adopted the 12-fold division, but called the signs rat, ox, tiger, hare, dragon, serpent, horse, sheep, monkey, hen, dog, and pig. Independently, the Aztec Indians devised a similar system. Research Zodiac
Carinaria is a genus of gasteropodous molluscs, of the order called Heteropoda or Nucleobranchiata, whose shells are known as Venus' slipper and glass nautilus. The gills are protected by a small and very delicate shell of glassy translucence. The creature itself is about five centimetres in length, and is of oceanic habits. It is so transparent that the vital functions may be watched by the aid of a microscope. Research Carinaria
The Ctenophora are a Phylum, sub-Phylum, order or class of animals represented by a number of marine forms (the sea gooseberries) which somewhat resemble jelly-fish. They are solitary, transparent, globular animals moving by means of ctenophores, or parallel rows of cilia disposed in comb-like plates. They develop no coral. Pleurotrachia (or Cydippe) may be taken as the type of the order, which includes the Beroidae, the Cestum or Venus' girdle, etc. Research Ctenophora
Droseraceae is a natural order of albuminous plants, mostly perennialbog plants, whose flowers are composed of five sepals, five petals, five, ten, fifteen or twenty stamens, and a single ovary. The leaves are usually covered with glands or glandular hairs. It contains six genera, including the sundew (Drosera), and Venus fly-trap (Dioncca). They have no known qualities except that they are slightly bitter. The leaves are generally circinnate in the bud, as in ferns. Research Droseraceae
Something which is insectivorous feeds predominantly upon insects.
Insectivorous plants and animals both occur.
Insectivorous plants are unique in their ability to digestanimalprotein as a source of nitrogen and are common to marshy ground where there is a shortage of nitrogen. Examples of insectivorous plants are the sundews, the butterwort, the bladderworts and the venus fly trap. Research Insectivorous
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Matt and Leela Probert
Abbreviations
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