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Sunspots and Starspots by John H. Thomas PDF

By John H. Thomas

ISBN-10: 0511457596

ISBN-13: 9780511457593

ISBN-10: 0521860032

ISBN-13: 9780521860031

Finished account of sunspots and starspots for graduate scholars, astronomers, geophysicists, area physicists and specialists in sunlight and stellar physics.

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1 Hale’s discovery of the sunspot magnetic field The most important breakthrough in our understanding of sunspots came in 1908 with the discovery by Hale of the strong magnetic field in sunspots. Hale (by then at Mount Wilson in California) measured the Zeeman splitting in magnetically sensitive spectral lines formed in sunspots, obtaining a field strength of some 3000 G, and he also detected the polarization of the split components of these lines (Hale 1908b). This was the first detection of an extraterrestrial magnetic field,9 which opened the way for the discovery of magnetic fields in other stars and other astronomical objects.

More recent observations give similar lifetimes with a FWHM of 1000 km and a spacing of 1400 km in the quiet Sun (Bray, Loughhead and Durrant 1984; Spruit, Nordlund and Title 1990). In magnetic regions the granules are smaller and last longer. Early spectroheliograms taken in the H and K lines of singly ionized calcium (Ca II) showed a mottled pattern dominated by a bright network, with some resemblance to B´enard convection (Deslandres 1910). 5 km s−1 and a scale of 26 Mm. Simon and Leighton (1964; see also Leighton, Noyes and Simon 1962) confirmed that this motion corresponded to a cellular pattern of supergranules with a characteristic diameter of 30 Mm, and radial outflows that fitted into the Ca II network; furthermore, they used a magnetograph to show that the Ca II emission coincided with a magnetic network, consistent with fields being swept aside and concentrated by the horizontal motion.

Two centuries later, when the sky was obscured by smoke from forest fires in Russia, chroniclers there reported, “there were dark spots on the Sun as if nails were driven into it” (Wittmann and Xu 1987). Progress since then has relied on technological advances. The invention of the telescope in the Netherlands in 1608 opened the possibility of detailed astronomical observations. News of the invention spread rapidly and reached Galileo Galilei (1564–1642) at Padua in June 1609. He used his improved instrument to observe the Moon and the Milky Way and to discover the satellites of Jupiter.

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Sunspots and Starspots by John H. Thomas

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