![]() ![]() Yet, being a woman, she was not given a formal appointment at Harvard, where she worked, until 1938 and was not appointed a professor until 1956. Her 1925 doctoral thesis laid the foundations for understanding the composition of the Sun and the stars. At the time, she wrote, “The enormous abundance derived for these elements in the stellar atmosphere is almost certainly not real.” Even scientists sometimes find it hard to accept new ideas that do not agree with what everyone “knows” to be right.Ĭecilia Payne-Gaposchkin (1900–1979). However, the idea that the simplest light gases-hydrogen and helium-were the most abundant elements in stars was so unexpected and so shocking that she assumed her analysis of the data must be wrong. The fact that our Sun and the stars all have similar compositions and are made up of mostly hydrogen and helium was first shown in a brilliant thesis in 1925 by Cecilia Payne-Gaposchkin, the first woman to get a PhD in astronomy in the United States ( Figure 15.3). (In our planet’s crust, the three most abundant elements are oxygen, silicon, and aluminum.) Although not like our planet’s, the makeup of the Sun is quite typical of stars in general. Examine that table and notice that the composition of the Sun’s outer layer is very different from Earth’s crust, where we live. ![]() The 10 most abundant gases in the Sun’s visible surface layer are listed in Table 15.2. All the other chemical elements (including those we know and love in our own bodies, such as carbon, oxygen, and nitrogen) make up only 2% of our star. About 73% of the Sun’s mass is hydrogen, and another 25% is helium. It turns out that the Sun contains the same elements as Earth but not in the same proportions. As explained in Radiation and Spectra, we can use a star’s absorption line spectrum to determine what elements are present. Let’s begin by asking what the solar atmosphere is made of. ![]() Table 15.1 Composition of the Sun’s Atmosphere Sunspots and Doppler shift in spectra taken at the edge of the Sun Solar constant × area of spherical surface 1 AU in radiusĭerived from luminosity and radius of the Sun Instrument sensitive to radiation at all wavelengths Gravitational acceleration at photosphere (surface gravity) ![]()
0 Comments
Leave a Reply. |