THE PLANET VENUS.

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Venus is respectively at its furthest distance from the Earth ,and very nearly at its nearest approach to it, will equallyserve to represent the comparative total amounts of lightwhich would be received from it on the two occasions in ques-tion, and the comparative brilliancy which it would display toan observer viewing it without the aid of a telescope , if in eachcase the whole of its surface turned towards him were illuminatedby the Sun’s light.

But, as is represented in the view of the phases of an inferiorplanet given in Fig. XXXVIII., the whole of the half of Venus seen from the Earth , when its position corresponds very nearly

Fig. XLVI.—Comparative diameters and phases of Venus : 1. When at its greatest dis-tance from the Earth ; 2. When gibbous; 3- When* seen at its greatest elongation from theSun ; 4. When at its greatest brilliancy; 5. When very nearly at its nearest approach to theEarth .

to the size of the fifth circle in Fig . XLVI., would be dark;while the whole of the smaller apparent disc represented bythe first circle would be bright. It is therefore clear, that insome intermediate position the greatest total amount of lightwill be actually received from it. And it is found that thisoccurs when its phase is as in No. 4 of the five figures shownabove, or when about one-fourth of its disc is illuminated.

In fact, all we need to do in order to determine the exact posi-tion in question, is first of all to draw a series of circles, whosediameters are greater or less according as Venus is nearer to