A new manual of the elements of astronomy, descriptive and mathematical .. (1868)
Kiddle, Henry, 1824-1891 · New York, Ivison, Phinney, Blakeman & co.; Chicago, S.C. Griggs & co. · leaf 175
imately by observing thephase of Mars when it varies most from the full. The following is themethod:— Let S (Fig. 101), represent the sun, E, the earth, and M, Mars, much Questions.—235. When is the motion retrograde ? Why ? When is the planet sta-tionary ? Why ? a. What is the arc of… … Fig. 101 enlarged for convenience of illustra- tion. The earth is obviously at thepoint of greatest elongation as seenfrom Mars; and hence the angleS M E is the largest possible. But thisis equal to a M d which measures thedeviation of the disc from the full;for the arc b a = ed; and taking e afrom…
Astronomy
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