1. Astronomer Edmund Halley was

attempting to calculate the distance from the earth to the sun in 1716. The

method he proposed used the transit of

Venus. His procedure is based on the idea of “Parallax”. This is the effect

when two observers are observing the same object from different orientations,

and therefore will observe a different distance to that object. In the case of

Halley that meant one at the north pole

and one at the south pole. Those

distances are measured, and then they form a triangle with the tip at Venus and

the other two vertices at the north and south pole. Based on trigonometry the distance

from the earth to Venus can then be determined. Kepler had already worked out

the relative distances of planets from the sun, so based on that ratio the astronomical

unit could be calculated.