In article ,
Earth Resident wrote:
How did scientists calculate the distance between earth and moon, earth and
sun etc.

The distance to the Moon was pretty easy: it's close enough that if you
observe it simultaneously from different parts of the Earth, its position
in the sky is a little different. Knowing how far apart the observatories
are, and measuring the difference in apparent positions, you can compute
how far away it is.

Earth and Sun is a lot harder. It's too far away for the same trick to
work very well. Observational astronomy is all angles, so you can measure
*relative* distances to the Sun and the planets quite well, but unless you
can measure one of those distances by some other means, you don't know the
absolute scale of the system.

One of Captain Cook's voyages had, as its primary objective, timing a
transit of Venus (a rare event, Venus passing in front of the Sun) from
the other side of the Earth from Europe. The difference in times would
give an absolute determination of the distance to the Sun. It didn't work
too well: because Venus's atmosphere blurs things, it's hard to decide
exactly when Venus crosses the edge of the Sun.

Various other approaches were tried. The best of the pre-spaceflight ones
was that the asteroid Eros occasionally passes near the Earth, and by
looking at how much Earth's known gravity disturbs Eros's orbit in such
an encounter, you can determine how close Eros came.

Plans for planetary probes made the matter much more urgent, because they
need precision navigation, and so extra effort was put into the problem.
Shortly before the first Mariners were launched, the distance to Venus was
successfully measured by radar, reducing the uncertainty from tens of
thousands of kilometers to less than one kilometer.

To put the final icing on the cake, in the late 1970s, the distance to the
Viking landers was measured to within meters by timing signals they
received and relayed back.
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MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |