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"Suppose a to be a stationary celestial object, then as the Earth makes her annual revolution around the Sun S, this object at one time will appear among the stars at e, but six months after, when the Earth comes to the opposite point in her orbit, the same object will be seen at c, the space from c to e being the annual parallax of the object a. But the distances of the stars are so great that the diameter of the Earth's orbit, or 190,000,000 of miles make no difference in their apparent places. Were the fixed stars within 19 trillions of miles, their distance could be told by their parallaxes." —Comstock, 1850

Annual Parallax

"Suppose a to be a stationary celestial object, then as the Earth makes her annual revolution around…

"If we suppose a spectator placed at G, in the Earth's center, he would see the moon E, among the stars at I, whereas without changing the position of the moon, if that body is seen from A, on the surface of the Earth, it would appear among the stars at K. Now I is the true and K the apparent place of the moon, the space between them, being the Moon's parallax." —Comstock, 1850

Diurnal Parallax

"If we suppose a spectator placed at G, in the Earth's center, he would see the moon E, among the stars…