THE TRANSIT OF VENUS.

Thames Star, Volume VI, Issue 1846, 2 December 1874, Page 2

THE TRANSIT OF VENUS.

?vV estreat the following highly interesting '.mc-le on the above subject from TheQiu'ver: — In the jc3r 1882,; on Dec. B*, will' occur ;i very remarkable phenomenon, and one that will greatly excite the scientific world, namely, the visible transit of the planet Venus across the disc of the sun. . '

Few persons now living hare beheld this rare phenomenon, nor is it probable that any person who may see it in 1882 will ever witness- the spectacle again. The trans-1 of the same planet across tho sun's disc, which will take place on the - Bfc!i of December 1874, will, doubtless, hare* the. effect of awakening -public interest at Jin early date to the-event of 1882. Venus appears to tile inhabitamts of the earth as thp most beautiful of all the planetary stars, being the second from the sun. and one of the two inferior planets having their orbits wit bin that of the earth. At the period of her greatest splendour, her light is to intense as to cast a, shadow up»a the earth's surface; and at certain seasons, after long intervals of time, she r&ay be seen shining with a pale silvery lustre in the full blaze of noonday. At her maximum brilliancy her light is estimated to equal that of twenty fixed stars. In the regions under the equator, at the time of her greatest elougation, she may bs seen high above * the horizon, burning with a clear and steady flame like a lamp —presenting an aspect far more splendid than in the latitudes of the north. She appears as an attendant upon the sun; and may be observed by those who descend into deep open pits or cavities of the earth, following in his track.'

This planet presents a very remarkable telescopic appearance. The shadows of great mountains break the circle of her glimmering light; and these mountains, according to Sehroeter, a famous German astronomer, have an altitude of more than twenty miles.

During herj transits her atmosphere, like a halo of faint penumbral light, is distinctly visible. Although about the size of the earth and performing her annual revolution in about the. same period, she is so much nearer the sun than we, that this luminary must appear twice as large to her inhabitants—if she have any—as to us, and the solar rays must descend upon her with a fervour twice as strong as that with which they reach our planet.

Even seen from the earth, so luminous is the aspect of Venus, at certain periods, that the body .of the planet may be discerned with wonderful distinctness through its transparent atmosphere. The great use of the observation of the transit of Venus, over the sun's disc is to determine the sum's horizontal parallax—an element of very great importance, since by it we are enabled to calculate the distance of the earth from the snn, and indirectly the distances of the other p'anets as well as fixed stars. The transits of Venus over the sun's centre occur alternately at intervals of 8, 105| and 1211 years. The last two occurred in the years 1761 and 1769; so that any one now living who beheld this latter must be over 100 years old to have seen it even in infancy. The following table exhibits in a con* venient form the transits that have taken place, and will take place for a period of more than 300 years, and also illustrates the order of the intervals at which these phenomena occur: — , Dec. 4,1639, to June 5, 1761 ... 1211 y«. June 5,1761, to June 3,1769 ... 8 "■ June 3,1769, to Dec. 8.1874 ... 105* " Dec. 8, 1874, to Dec. 6, 1882 ... 8 " Dec. 6, 1882, to June 7, 2004 ... 121* " June 7, 2004, to June 6,2012 ... 8 "

The position of the planet is apparently very different as seen by different observers during a transit; that is, to a person on one side of the earth, at the same instant of time, it will seem on a different part of the sun's disc, from its apparent .position viewed from the other side ; and it is by a comparison between these apparent different, positions—a» viewed at different places during the transit, that we obtain a basis for calculating and working out some of the most wonderful problems ot astronomical science ever mastered by the mind of man. . Among these great solutions, the most important is the sun's horizontal pa-rallax,-which, as determined by the observations on the transit of 1769, is eight seconds and six-tenths; or, according to Professor Encke, as the result. of- his observations, 8 f5776 sees.

*Our reader* will obsarT* thut.tbit and all the following dates are computed from Greenwich mean time.