Willson, Robert Wheeler, 1853-1922 · Boston, New York Ginn & company · leaf 158
g. 74. Fi and F^ are the foci, AB the major axis, and C, which bisectsboth FiFj and AB, is the center of the ellipse. PF^ is the radius THE MOTIONS OF THE PLANETS 145 vector from any point P to F^, and PF^ the radius vector to F^.They are usually represented by r^ and r^. r^ + r^ is a constant… … Fig. 74. Fundamental Points and Lines ^ C is usually representedby a, and CF^ or CF2 by c. Since 2 c equals thedistance between the foci, and 2a + 2c the length of the thread,the shape and size of the ellipse are completely fixed by the valuesof a and c. The ratio c/a is called the eccentricity and…
Astronomy
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