Moulton, Forest Ray, 1872-1952 · New York, The Macmillan company · leaf 274
er the planets whose orbits are outside thatof the earth. They are called the superior planets. Sup-pose the periods of revolution of the earth and Mars, forexample, have been determined from long series of obser-vations. This can be done without knowing anything abouttheir actual or relative… … FiG. 84. - Finding the distance of aninferior planet. 228 AN INTRODUCTION TO ASTRONOMY [ch. viii, 144 quired for it to move from a certain position with respectto the sun back to the same position again. For example,when a planet is exactly 180° from the sun in the sky, asseen from the earth, it is…
Astronomy
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