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The parts of the atmosphere are also labeled the photosphere, chromosphere, and corona. Parts of the Sun: This illustration shows the different parts of the Sun, from the hot core where the energy is generated through regions where energy is transported outward, first by radiation, then by convection, and then out through the solar atmosphere. The Layers of the Sun beneath the Visible Surfaceįigure 3. This is how we first discovered that the Sun’s atmosphere had a temperature of more than a million degrees. It was not until 60 years later that astronomers discovered that this emission was in fact due to highly ionized iron-iron with 13 of its electrons stripped off. In the nineteenth century, scientists observed a spectral line at 530.3 nanometers in the Sun’s outer atmosphere, called the corona (a layer we will discuss in a minute.) This line had never been seen before, and so it was assumed that this line was the result of a new element found in the corona, quickly named coronium. (Scientists call such a hot ionized gas a plasma.)
#SUN CORONA HELIUM FREE#
This removal of electrons from their atoms means that there is a large quantity of free electrons and positively charged ions in the Sun, making it an electrically charged environment-quite different from the neutral one in which you are reading this text. In fact, the Sun is so hot that many of the atoms in it are ionized, that is, stripped of one or more of their electrons. Most of the elements found in the Sun are in the form of atoms, with a small number of molecules, all in the form of gases: the Sun is so hot that no matter can survive as a liquid or a solid. (And, as we will see, the composition of the Sun and the stars is much more typical of the makeup of the universe than the odd concentration of heavier elements that characterizes our planet.) It was 3 years after her thesis that other studies proved beyond a doubt that the enormous abundance of hydrogen and helium in the Sun is indeed real. 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.īefore Payne-Gaposchkin’s work, everyone assumed that the composition of the Sun and stars would be much like that of Earth. 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 2). 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.
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Cecilia Payne-Gaposchkin (1900–1979): Her 1925 doctoral thesis laid the foundations for understanding the composition of the Sun and the stars. The Abundance of Elements in the Sunįigure 2. (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 1. 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. 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) Although some of the terms in that table may be unfamiliar to you right now, you will get to know them as you read further. Some of the basic characteristics of the Sun are listed in Table 1.
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(credit: modification of work by SOHO/EIT/ESA) Earth and the Sun: Here, Earth is shown to scale with part of the Sun and a giant loop of hot gas erupting from its surface.