William and Caroline Herschel: Incredible Siblings of Science Shreyans Parekh Astronomy 007 Professor Langacker

Biographies Major accomplishments together: 1. Observations helped to double the known size of universe 2. First to accurately describe Milky Way 3. Mapping of spiral nebulae 4. Discovery of Uranus (1781) 5. Pushed forward science of building telescopes Caroline Herschel  Born March 16, 1750 in Hanover, Germany  Mother believed women should not be educated  In day, she made calculations for William and at night she explored universe herself  First lady of astronomy  First lady to discover comet  Pioneer in study of comets William Herschel  Born November 15, 1738 in Hanover, Germany  Successful music teacher and bandleader  Music led him to math and astronomy  Appointed court astronomer to King George III  Became one of most notable observers in history of astronomy  Pioneer in study of stars

Charting Stars and Milky Way: Part 1  First astronomers in history to do systematic survey of the night sky  Discovered many stars that they previously observed as single stars were resolving, because of larger telescopes used, into double (or binary) stars  Stars appeared to move around each other, suggesting gravitational influence between them  Showed that Kepler’s laws of planetary motion and Newton’s law of universal gravitation applied, not only to the planets and sun of our solar system, but to distant stars as well and were truly universal  Stars were so distant that they were not able to determine their distances with parallax, so they came up with another method for determining the shape of the Milky Way Source:

Charting Stars and Milky Way: Part 2  Noticed that density of stars varied depending upon what region he was looking at  Two factors could account for this varied distribution of stars: 1. Either the stars were closer together in the regions where they appeared to be more compacted 2. Stars were spaced apart more or less uniformly, and where the stars seem to be the densest is where the Milky Way extended out the furthest *  Discovered greatest density of stars was around the Milky Way and lowest density was away from the Milky Way  Concluded shape of Milky Way “detached nebulae” was a disk (grindstone) Source:

Cataloguing Nebulae  Over 25 years, he catalogued and investigated nebulae, milky luminous patches in sky and verified that they were clusters of countless stars  Expanded list of nebulae compiled by one of his contemporaries Charles Messier and believed they were “island universes”  Announced discovery in his Catalogue of 500 New Nebulae and Clusters of Stars  Identified about 2,500 planetary nebulae (hazy clouds that surrounds stars) and more than 800 binary stars (pairs of stars orbiting common center of galaxy)  In 1835, Lord Rosse designated nebulae that resembled whirlpools of light were spiral nebulae Herschel’s 40-foot reflector Source:

 Tried to find relative distances of stars and each other and from Sun  Definition: pair of stars bound together by gravity  Discovered binary stars in 1802 and described them as “union of two stars, that are formed together in one system, by the laws of attraction.”  Concluded from the motions of double stars that they are held together by gravitation and that they revolve around a common center, thus confirming the universal nature of Newton's theory of gravitation Discovery of Binary Stars Source:

“Grindstone” Model of Universe  Definition: Sun is located near the center of the of a wheel-shaped group of stars. Milky Way is flat like a grindstone.  Counted stars along 683 lines of sight  Assumed all stars are same luminosity, and that they could see edges of the universe (underestimated size of universe)  Accomplishment: established idea of the Milky Way as an autonomous celestial body, and extended boundaries of universe much further than anyone had previously thought them to be  Erroneous assumption: dark regions represent gaps in the Milky Way (are in fact dark clouds of dust) Herschel’s Milky Way and detached nebulae model Source:

Discovery of Uranus  Discovered on March 13, 1781 and was first planet discovered in modern times  While systematically searching for double stars, Herschel discovered what he thought to be a comet but due to its completed orbit, found it was a planet  Called Georgium Sidus after King George III of England, but renamed to Uranus from Greek meaning “sky”  Credited with discovering two moons of Uranus (Titania and Oberon) as well as two moons of Saturn (Enceladus and Mimas) Image taken by Voyager 2 Source:

Interesting Facts  William was a prolific telescope maker  His 40-foot reflector was largest in the world until the 1840s, when Lord Rosse completed construction of Leviation of Parsonstown  Discovered infrared radiation by passing sunlight through prism and holding a thermometer before red end of the spectrum  Coined term “asteroid” to describe star- like appearance of small moons  Wild speculator: believed all planets and even the Sun were inhabited by life forms Source: