Final answer:
William Herschel discovered Uranus, contributed to the understanding of the Milky Way's structure, and measured star brightnesses. Edmund Halley predicted the orbit of the comet named after him and mapped the southern skies. Friedrich Bessel performed the first accurate measurement of a star's distance, which was an important step in determining the scale of the universe.
Step-by-step explanation:
Contributions of William Herschel, Edmund Halley, and Friedrich Bessel
William Herschel was an accomplished astronomer known for his discovery of the planet Uranus, the construction of large telescopes, and significant measurements of astronomical objects. His work on the Sun's place in the Galaxy and its motion through space, along with his cataloging of the comparative brightnesses of stars, helped pave the way for modern astrophysics. Herschel's methodical counting of the stars with his sister Caroline led to the understanding that the Milky Way is disk-shaped, with the Sun near its center.
Edmund Halley's pivotal role in the study of comets, particularly the famous Halley's Comet, is a hallmark of his career. His prediction of the comet's orbit was an outstanding achievement and he contributed to various fields of science, including encouraging and financing Isaac Newton's masterpiece, the Principia. Halley's work in mapping the southern skies and his early involvement with the Royal Society emphasize his impact on the field of astronomy.
Friedrich Bessel performed the first authenticated measurement of a star's distance, specifically 61 Cygni. This breakthrough in measuring stellar parallax opened a new window for understanding the scale of the universe. Bessel's achievement was remarkable for overcoming a challenge that had stumped astronomers for nearly a century.