Mask of the Sun: The Science, History and Forgotten Lore of Eclipses by John Dvorak

Author:John Dvorak [Dvorak, John]
Language: eng
Format: azw3
Publisher: Pegasus Books
Published: 2017-03-07T05:00:00+00:00

Today it is easy to trivialize what De La Rue and Secchi had done. But one must remember how little was known about the physical character of the Sun and the Moon when they were doing their work.

In 1836 Baily had taken precious moments during totality to carefully study the dark silhouette of the Moon through his telescope, wondering if he might see a few bright spots of sunlight that would indicate the Moon’s interior was cavernous. There were also those who thought the Moon’s surface consisted of a thick layer of material that was so loose that if someone tried to stand on it, they would immediately sink down and disappear.

Ideas about the Sun were even stranger, that is, by our standards today. In the 1810s William Herschel, the discoverer of the planet Uranus and then one of the world’s foremost astronomers, had studied sunspots and concluded that they were openings to a cold dark interior and that the part of the Sun that we could see was actually a thin shell that consisted of a vast luminous ocean. By the 1860s the idea of a cold interior had been discarded in favor of a luminous ball, but exactly what was the Sun? Was it a solid, a liquid, or a gas? The blinding brilliance of sunlight had prevented progress on this question. And that is why a study of total solar eclipses took center stage. One should be able to learn much about the Sun by studying the prominences. And there was a new tool, developed in the 1850s, that would lead the way—spectroscopy.

As in many things, Newton had led the way when he made a small circular hole that allowed a beam of sunlight to enter a darkened room, then using a prism spread the sunlight into the familiar rainbow of colors. In 1814 Joseph von Fraunhofer, a glassmaker in Germany, greatly improved on Newton’s original experiment by, among other things, using a thin slit instead of a small circle. He also used multiple glass prisms that allowed him to make wider rainbows that he then studied in detail, noticing that hundreds of dark lines appeared. The more prominent of these dark lines he designated with capital letters from A to K, omitting I and J because of the difficulty in distinguishing the two letters in print. The mystery of the dark lines was solved in 1859 by Gustav Kirchhoff. He showed that a unique set of dark lines could be associated with each chemical element. For example, the C and F lines identified by Fraunhofer corresponded to strong lines produced by Kirchhoff when he heated hydrogen gas in a glass tube. The E line Kirchhoff associated with iron, the G line with calcium and the D line with sodium, such as that found in table salt. To make these determinations, Kirchhoff had invented a new type of scientific instrument, the spectroscope. Suddenly, the world of inquiry became much larger for astronomers. They could now use spectroscopes

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.