William Herschel


May 22, 2022

Sir Frederick William Herschel (German: Friedrich Wilhelm; Hanover, November 15, 1738 - Slough, August 25, 1822) was a naturalized British German astronomer, physicist and composer. He was the discoverer of the planet Uranus.


He was born in Hanover in 1738 to Isaac Herschel and Anna Ilse Moritzen. His father, a musician of the Hanoverian infantry, managed to transmit the passion for music to all of his children (of which six out of ten lived to adulthood) except the eldest daughter. At the age of fourteen, after completing his studies at the garrison school, William joined his father's gang and, shortly after the outbreak of the Seven Years' War, left military service to emigrate with his brother Jacob to England. Here, in a few years, he managed to gain a solid reputation as a soloist (oboe and violin) and music teacher. Self-taught, he began the study of astronomy and, in 1776, he began to build the first telescopes, first of the Gregorian type and then of the Newtonian type. On March 13, 1781, during a review of the skies aimed at the discovery of double stars to be used for the measurement of stellar parallaxes, he accidentally discovered what turned out to be the planet Uranus. Convinced that he had discovered a simple comet, Herschel communicated the news to the Bath Philosophical Society and the Royal Society of England in a short essay entitled Account of a Comet. In 1782 he was appointed Astronomer to the King (a position specially designed for him, different from that of Royal Astronomer, at the time attributed to Nevil Maskelyne) and moved from Bath to Windsor, lodging first in Datchet and then in Slough. King George III, in addition to an annuity of £ 200 a year, gave him a sum of £ 2,000 to build a large reflecting telescope, with a primary mirror over a meter in diameter and a focal length of 12 m (40 ft. ). With the mirror telescopes, which he himself built and which turned out to be among the most powerful of the time, he made some notable discoveries: in 1787 Titania and Oberon, satellites of Uranus. This confirms his great observational skills, given that, for the next twenty-five years, no one else was able to identify them; in 1789 Mimante and Enceladus, satellites of Saturn.He was also a pioneer in galactography. In 1784, in fact, he decided to count the total number of stars through a sample calculation. Knowing the precise number, it would have been possible to understand the shape of the galaxy. He divided the sky into 683 sample zones and calculated the number of stars in each of them. He discovered that the number of stars was maximum on the plane of the Milky Way and minimum perpendicular to it. There were three hundred million stars and the galaxy was shaped like a millstone, 7,000 light years long and 1,300 wide, with the Sun in a not too privileged position. Although his data are far inferior to the real one, the pioneering spirit of the studio and the difficulty of operating without being able to take photographs is undeniable. It took him a century before others tried to get better measurements. In "On the Construction of the Heavens" (1785) he was able to describe the three-dimensional structure of the Milky Way. As a result of his observations of the celestial sphere, these three catalogs contained the description of about 2 500 nebulae, which were presented as the birthplaces of galaxies. Finally, Herschel was responsible for the discovery of infrared rays, made with an ingenious experiment carried out in 1800. he placed a mercury thermometer in the spectrum produced by a glass prism, to measure the heat of the different colored bands of light. He found that the thermometer continued to rise even after moving beyond the red edge of the spectrum, where there was no longer visible light. It was the first experiment that showed how heat could be transmitted thanks to an invisible form of energy. He theorized subsistence d