Elements of astronomy ... with explanatory notes, and questions for examination (1855)
Brocklesby, John, 1811-1889 · New York, Farmer, Brace & co. · leaf 227
ry and Yenus, his illuminated sur-face is nevertheless subject to slight fluctuations in form.At the time of opposition the planet is exactly circularbut is usually seen of an oval shape, owing to the cir-cumstance that we then view it out of the line joining thecentre of the planet and the sun,… … PHASES OF MARS. earth, E and El 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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