With the transit of Venus in 1769 the astronomers for the first
time managed to measure the distance to the Sun fairly accurately.
But the relative distances were already well known.
Nicholas Copernicus (14731543) understood that the planets,
including the Earth are orbiting the Sun and that the Earth is
not in the center of the Universe. In 1543 he published a
describtion of the Solar system. It gave a determination of the
mutual distances between the Earth and the Sun and Venus and the
Sun.
This is how he calculated it:

Orbits of Earth and Venus.
D is the center of Venus'orbit.
C is the center of Earths orbit.
At point F the "evening star" Venus is visible from
Earth being in point B. At point E the "morning
star" Venus is visible from Earth being in point
A
Illustration: astronomy.no

Copernicus used these, observed maximum angular distances between
the Sun and Venus (numbers are from observations made in the
antique!):
Angle DBF = 47.3 degrees, angle DAE = 44.8 degrees.
From here on we need the trigonometric sine function.
It follows that BD=DF/sin 47.3 and AD=DE/sin 44.8 where
DE=DR=radius in Venus' orbit.
Radius of Earths orbit AC is one half of BD+AD.
This gives that AC/DE=1/2 [ (1/sin 47.3) + (1/sin 44.8) ]
And therefore DE/AC=0.7196 which is the value calculated by
Copernicus as the relationship between the radies of the
orbits of Venus and the Earth.
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Major celestial events in Norway 20102015