As powerful as spectroscopy and photography were, they could not help astronomers work out the distances to the stars.
Industrial advances in the early 1800s, however, made possible more accurate instrumentation and optics. The
Friedrich Bessel was the first to capitalize on these advances.
In 1838, by measuring the slight positional shift of the star 61 Cygni with respect to more distant background stars—an effect known as parallax—he estimated a distance for that star of 35 trillion miles (56 trillion km), or about 6 light-years.
Within two years, the distances to two other stars, Alpha Centauri and Vega, were determined using the parallax effect. In the decades that followed, many more distances were calculated and scientists realized that the universe was far more vast than once thought. No one, however, was prepared for how big it would "grow."