To the ancient Greeks and Romans, the Earth was both the centre of the Universe and its most important constituent. Although Greek philosophers had some knowledge of the distance to the Moon, it was only with the invention of the telescope in the seventeenth century that anyone began to understand how far the stars were away from us. Galileo was the first person to use a telescope for astronomical observations, and he was surprised to discover that even with the aid of his telescope's magnifying power the stars still appeared only as points of light, not as spheres like the Sun and planets. This could only mean that they were very much farther away than the Sun and planets. He also found a multitude of stars visible through the telescope but unvisible to the naked eye, and his telescope revealed the Milky Way itself to be made up of swarms of individual stars.
At the same time, in the early seventeenth century, that Galileo was opening a new window at the Universe, Johannes Kepler was developing the basis of a theoretical understanding of our Solar System. His discovery of a relationship between the time it takes for a planet to orbit once around the Sun and the average distance of that planet from the Sun led, by the 1670s, to a reasonable accurate estimate of the distance from the Earth to the Sun. Kepler's observations also provided one of the foundations for Isaac Newton's study of gravity.
It took 150 years for astronomers to refine and improve both observations and their theories to the point where accurate distances to a few stars were first estimated, in the late 1830s. Such estimates, and those of the twentieth century, provide a crucial steppingstone in measuring the scale of the Universe, right out to the most distant galaxies.