How can astronomers measure distances directly to worlds like Venus, Mars, the Moon, or the satellites of Jupiter?
The first method was the parallax.
The first accurate measurement of the astronomical distances was done by an Italian astronomer, Cassini.
He used the method of parallax.
This method is based on the idea that the Earth is in two different observational points after six months, because it rotates around the Sun.
Then we see a distant object moving because we are seeing it from a different point of view and the apparent movement is related to the movement of Earth and the distance of the object. The closer it is the larger the movement will appear.
The picture should clarify better the method.