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VENUS

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Originally appearing in Volume V27, Page 1014 of the 1911 Encyclopedia Britannica.
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VENUS , in See also:

astronomy, the second of the See also:major See also:planets in the See also:order of distance from the See also:sun, and moving next within the See also:orbit of the See also:earth. Its See also:symbol is ?. At inferior See also:conjunction it approaches nearer to the earth than any other major See also:planet, but in that position it is practically invisible. Its apparent See also:motion may be described as an oscillation from one See also:side of the sun to the other, the See also:complete See also:period of which is 1.6 years, and the greatest See also:elongation about 450 on each side of the sun. When See also:east of the latter it appears as the " evening See also:star " in the See also:west after sunset, while near western elongation it is seen as the " See also:morning star " before sunrise. In these aspects it was known to the ancients as "Earrepos, See also:Hesperus, and `Ewv4opos or 4'our4 opos, See also:Phosphorus. The eccentricity of its orbit is smaller than that of any other planet except See also:Neptune. Notwithstanding the near approach of Venus to the earth, its situation relative to the sun is unfavourable to the study of its See also:physical constitution. Near inferior conjunction only a narrow See also:crescent of See also:light is visible; and when, as the planet moves away, this crescent becomes broader, the distance of the planet See also:con- stantly increases. When it appears as a See also:half-See also:moon it is at a distance of more than two-thirds that of the sun, and nearly See also:double the distance of See also:Mars in opposition. The difficulty of reaching any conclusion on the subject of its constitution is heightened by the seeming See also:absence of any well-marked features on the visible See also:part of its brilliant See also:surface. In the See also:telescope it presents much the See also:appearance of burnished See also:silver, without spot or blemish.

It is true that observers have from See also:

time to time thought they could detect slight See also:variations of shade indicating an axial rotation. As far back as 1667 G. D. See also:Cassini thought he saw a See also:bright spot near the See also:southern See also:horn, observations of yeno°us. of which gave a period of about 23 See also:hours. In 1726 of Ven See also:Francesco See also:Bianchini (1662–1729), a papal See also:chamberlain, made similar observations from which he inferred a period of more than 24 days. It was shown, however, that the observations of Bianchini could be reconciled with those of Cassini by supposing that, as he observed the planet See also:night after night, it had made one rotation and a little more. J. H. Schroeter also found a revolution of less than 24 hours. But See also:Sir W. See also:Herschel, as in the See also:case of See also:Mercury, was never able to detect any changes from which a period of rotation could be determined. During the years 1888–189o, G.

See also:

Schiaparelli made an exhaustive study of the whole subject, the results of which were summed up in five brief notes, read to the Lombardian See also:Academy of Sciences during the See also:year 1800. His See also:general conclusion was that Venus always presents the same See also:face to the sun, as the moon does to the earth. The same result has been reached by the observations at the See also:Lowell See also:Observatory. The inference that the axial rotation is at least much slower than that of the earth is strengthened by the See also:measures of different diameters of the planet made while it was in transit across the disk of the sun in 1874 and 1882. These show no measurable See also:ellipticity of the disk, but they are not sufficiently accurate to See also:lead to any more precise conclusion thanthat just stated. Still, the difficulty and uncertainty attending all observations hitherto made upon the disk are such that no conclusion respecting the time of rotation can be regarded as established. Against the view of Schiaparelli is to be set the See also:great improbability that a See also:body so distant from the sun as Venus could be permanently so acted upon as to keep its axial rotation in precise coincidence with its orbital motion. Only one way seems to be open for settling the question; this is by spectroscopic observations of the displacement of the spectral lines at the two limbs of the planet. Attempts by this method have been made by A. A. Belopolski at Pulkova, and by the astronomers of the Lowell Observatory. It is, however, found that the amount of displacement is so small that it has evaded certain detection up to the See also:present time.

Belopolski's measures were decidedly in favour of an axial rotation, while the Lowell results were not. Other observations than those we have cited show that Venus is surrounded by an See also:

atmosphere so filled with clouds that it is doubtful whether any view of the solid body of the Atmoplanet can ever be obtained. The first See also:evidence in See also:sphere of favour of an atmosphere was found in the fact Venus. that, when near inferior conjunction, the visible outline of the thin crescent extended through more than 18o°. Most remarkable was an observation by See also:Chester See also:Smith Lyman at New Haven during the conjunction of 1866, when the planet was just without the sun. A thin See also:line of light was supposed to be seen all See also:round the See also:limb of the planet most distant from the sun. But as no such appearance was seen during the approach of the planet to the sun at the transits of 1874 and 1882, when the conditions were much more favourable, it seems likely that such observations are the result of an See also:optical illusion. During the latter of the two transits the phenomena of this class observed were of an unexpected See also:character. Not a trace of the planet could be seen until it began to impinge upon the See also:solar disk. When about half of its See also:diameter had entered upon the sun the outline outside the disk of the sun began to be marked by broken portions of an arc of light. This did not begin at the point A (fig. 1) farthest from the sun, as it should have done if dun Sufi wholly to See also:refraction, but immediately at the sun itself, as sf''lown in the cut at the point B. Portions of this arc were formed one by one at various other points of the dotted outline, and when the planet was about three-fourths upon the sun the are- was completed.

But there was no strengthening of the line at the See also:

middle point, as there should have been if due to refraction. Yet refraction must have played some part in the phenomenon, because otherwise no See also:illumination could have been visible under the circumstances. The most satisfactory explanation seems to be that of H. N. See also:Russell, whose conclusion is that the atmosphere is so permeated with See also:fine particles of vapour up to its See also:outer limit as to be only translucent without being fully transparent. Thus what is seen is the irregular reflection of the light at an extremely small See also:angle from the particles of vapour. The question whether Venus has a See also:satellite has always interested astronomers. During the 17th and 18th centuries Cassini at See also:Paris and See also:James See also:Short (1710–1768) in See also:England, as well as other observers during the same period, saw an ssateiNiupF-'See also:sea. e See also:object which had the appearance of a satellite. But as no such object has been seen by the most careful See also:search with the best See also:instruments of See also:recent times, the supposed object must be regarded as what is known to the See also:practical astronomer as a " See also:ghost " produced by refraction from the lenses of the See also:eye-piece, or perhaps of the object-See also:glass, of the telescope. See also:century. Venus passes the seen against the sun only fofollowing See also:list of See also:dates from rence.

1518 See also:

June 2. 1526 June I. 1631 See also:December 1639 December 1761 June 6. The first of these transits actually seen was that of 1639, which was imperfectly observed by See also:Jeremiah Horrox (1619-1641) shortly before sunset. See also:Special See also:interest in them was first excited by See also:Edmund See also:Halley a century later, who showed that the See also:parallax of the sun could be determined by observing transits of Venus from regions of the earth's surface where the displacement by parallax was greatest. Governments, scientific organizations and Individuals fitted out expeditions on a very large See also:scale to make the necessary observations upon the four transits which have since occurred. The disappointing character of the results so far as the solar parallax is concerned are stated in the See also:article PARALLAX, SOLAR. It may be said in a general way that the observations, even when made by experienced astronomers, exhibited irregularities and discordances several times greater than one had a right to expect. Other methods of deter-See also:mining the distance of the sun have been so perfected that the results of these transits now See also:count but little. (S.

End of Article: VENUS

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VENUE (derived through the French, from Lat. venire... 		[next]
VENUSIA (mod. Venosa, q.v.)

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