Hale, George E. (1868-1938) - discovered the magnetic properties of sunspots in 1908. He also founded the observatory at Mt. Wilson. Halley, Edmond (1656-1742) - the second Astronomer Royal of England. He attempted to measure the Earth/Sun distance using the transit of Venus. He also correctly predicted the return of the comet that bears his name. Hell, Abbe Maximillian (1720-1792) - a Jesuit priest who became the director of the Vienna Observatory in 1755. For 36 years he published yearly epheremides and in 1761 he observed the transit of Venus. Later he was falsely accused of adjusting his measurements of the transits in order to match other observations. Henderson, Thomas (1798-1844) - the second director of the Royal Cape Observatory and later the first Astronomer Royal of Scotland. Two months after Bessel published the parallax of the star 61 Cygni, Henderson announced he had found the parallax of the star Alpha Centauri. Herschel, Caroline (1750-1848) - sister and assistant to William Herschel. In 1786 she discovered the first of eight comets. After the death of her brother she published the catalog of his observations. Herschel, John (1792-1871)- son of William Herschel who continued his fathers work in astronomy. He spent part of his life at the Cape of Good Hope in South Africa measuring the stars of the Southern Hemisphere. He eventually became president of the Royal Astronomical Society. Herschel, William (1738-1822) - creator of some of the best (and largest) reflecting telescopes of the eighteenth century. He was determined to map the entire night sky of the Northern Hemisphere. In doing so in 1781 he discovered the planet Uranus. His observations of double stars proved for the first time that they were gravitationally linked. Hertzsprung, Ejnar (1873-1967) - in 1911 plotted the first two-dimensional diagram of the absolute magnitude versus spectral type for stars. In 1913 it was also independently created by Henry Norris Russell. The diagram today is called the Hertzsprung-Russell (H-R) Diagram and is an invaluable tool to astronomers. Hevelius, Johannes (1611-1687) - published one of the first maps of the Moon in 1647 titled Selenographia, many of the labels he applied to the features are still in use today. After his death a celestial atlas he created was published which included many new constellation several which are still in use today. Hooke, Robert (1635-1703) - English scientist and inventor. He attempted to measure the parallax of the star Gamma Draconis by using a telescopic devise of his invention named the "Archimedean Engine". He was never able to correctly determine the parallax. Horrocks, Jeremiah (1618-1641) - English astronomer and one of only two people known to have viewed the transit of Venus on December 4, 1639. Hubble, Edwin (1889-1953) - American astronomer who using the Mt. Wilson Observatory studied the motions of galaxies. In 1929 he announced what has since been called "Hubble's Law" which relates the distances of galaxies to the speed in which they are traveling. Relating them is a term called the "Hubble Constant". Huggins, Sir William (1824-1910) - English astronomer who was one of the first scientist to use spectroscopy in astronomy. He also developed a way to take photographs of spectra and was the first to notice the red- and blue-shifting of the light of stars caused by the Doppler Effect. Huygens, Christian (1629-1695) - Dutch scientist who when studying Saturn with a telescope equipped with lenses of his own design was the first to explain the the material surround the planet were actually thin rings. He also discovered a moon orbiting the planet.