Brocklesby, John, 1811-1889. [from old catalog] · New York, Sheldon and company · leaf 233
Mercury and Yenus, his illuminated sur-face is nevertheless subject to slight fluctuations in form.At the time of opposition the planet is exactly circularbut in other positions is oval, owing to the cir-cumstance that we then view it out of the line joining thecentre of the planet and the sun, and… … PHASES OF MARS. earth, E and E1 two positions of the earth, and M, Mars.Now since half of the surface of Mars is illumined by thesun, the boundary of the visible portion, as seen fromthe sun, may be represented by the line ab drawn perpen-dicular to the line joining the centres of the sun andMars.…
Astronomy
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