Reading Nature, Observing Science: Examining Material Practices in the Lick Observatory Archives and Kenneth S. Norris Papers

Understanding the Sun

The Lick Observatory eclipse expeditions strove to answer the following questions:Astrophysicists today understand sun spots to be magnetic areas of the sun's surface that appear dark because they are cooler than their surroundings (but still approximately 4500 degrees Celsius). The number and location of sun spots varies over an eleven year cycle, which coincides with magnetic activity and solar brightness. The Solar Corona is the sun's outer atmosphere and is understood to be made up of super-heated gasses that are formed into loops, plumes, and streamers by the sun's magnetic field.

Though sun spots were first observed by Galileo in 1610, the nature of both sunspots and the solar corona fascinated and mystified astronomers through the early nineteenth century. With the advent of astrophotography, astronomers could carefully observe and record these phenomena. In the carefully observed drawing by Langley the sun spot looks like a dark opening in a dense wall of foliage-like fibers. In Trouvelot's illustration, the sun spots are holes connected by masses that we would now understand to be prominences, but which here resemble muscle tissue. In both images we see careful observation of the visually available information--an interruption of the surface; a darker center surrounded by areas of movement--but interpreted with reference to familiar forms. ‚ÄčThese images reflected and informed Lick Director Edward Holden's thinking about the sun: both Trouvelot and Langley were in correspondence with the astronomers at the Lick, sharing sketches of their observations, and Holden pasted a copy of Langley's Sun Spot engraving into his scrapbook.

Similarly, the sketches astronomers made of the corona at this point in time accurately record the shapes of the corona, but fail to understand the forces behind it. Edward Holden, the founding Director of the Lick, hypothesized that the "coronal filaments were produced by streams of meteorites falling into the sun." John Schaeberle, the astronomer who designed the 40ft camera used on the majority of the eclipse expeditions, proposed that the coronal forms were "produced by volcanic forces emanating from the sun spots." It was not until the 1930s that the magnetic nature of the corona was understood amongst astronomers.

Today, astronomers can capture the the movements of the sun's surface with video and at multiple wavelengths. However, we still have questions about this giant magnetic star.


 

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