Development of a New Astronomy

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The decade opened with a very bright comet and closed with the return of perhaps the most famous of all comets, Halley's comet in 1910. These events punctuated a decade that tested astronomical superstitions and speculations with new and more-accurate observing tools and methods.

The wildest speculation at the dawn of the 20th century was one promoted by Percival Lowell, the featured scientist of the decade. He was convinced that features observed on the planet Mars were artificial canals that had been built by intelligent beings and that seasonal changes on Mars were the result of irrigated fields. He assumed that all planets began as wet worlds and dried over time, so Mars was much older and more evolved than Earth. He and others believed that a Martian race would be highly advanced and have much to teach humans. Contact with them offered a driving reason behind further study of Mars and the scientific exploration of space. Lowell dedicated his life and fortune to the task, building an observatory in Arizona, creating new spectral analysis techniques, and spurring the improvement of photographic and observational methods. The debate about Mars dominated the early part of the decade and reached a peak in 1907 when Mars made its closest approach to Earth. The controversy and how it was addressed and resolved are the major topic of this chapter.

The only way for humans to fly in 1901 was in a hot-air balloon. But one visionary, Russian teacher Konstantin Tsiolkovsky (1857-1935), knew that spaceflight was at least possible. He developed the rocket equation (see sidebar on page 10) the same year (1903) that the American Wright brothers made the first powered flight. Tsiolkovsky's achievement and influence on future scientists is briefly addressed in the chapter. Several decades pass before progress in aviation and engineering catch up with his designs.

The second major topic of the chapter is the transformation of astronomy from teaching and measuring to studying the physical nature of objects in space. The transformation was fueled by an explosion of data collected in sky surveys in the previous decade. As more spectra were taken with new telescopes and improved photographic techniques, differences among stars emerged. There were no professional female astronomers during this time period, but several women made major contributions to the new science. To organize the hundreds of spectra coming into Harvard, "computer" Williamina Fleming (1857-1911) invented a class system that divides the spectra by temperature, a system still in use today. Her system facilitated the discovery of the correlation between stellar temperature and brightness that is a building block of stellar evolution and the major topic of the next decade. Another Harvard "computer," Henrietta Leavitt (1868-1921), noticed that a certain type of variable star's brightness was related to its period. This discovery provided a "yardstick" for measuring astronomical distances in the next decade.

University of Chicago astronomer George Ellery Hale (1868-1938) was one of the first scientists to embrace the "new astronomy" and contributed much of the new data on the Sun and the stars. Hale had successfully founded the Yerkes Observatory in 1897 and outfitted it with the biggest telescope in the world, a 40-inch (1-m) refractor. To see more detail in near objects and to observe more-distant faint objects, he needed a large reflecting telescope. Hale's construction of the 60-inch (1.5-m) reflecting telescope atop Mount Wilson in California in 1908 marked a change in astronomical observing. From then on, the largest and best telescopes were reflectors (see figure on page 13). These new telescopes let astronomers see farther into space than ever before and led


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