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On Solar Granulations, Limb Darkening, and Sunspots: Brief Insights in Remembrance of Father Angelo Secchi

Author(s): Robitaille P.-M.

Journal: Progress in Physics
ISSN 1555-5534

Volume: 3;
Start page: 79;
Date: 2011;
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Keywords: Solar Granulations | Limb Darkening | Sunspots | gaseous solar interior

Father Angelo Secchi used the existence of solar granulation as a central line of reasoning when he advanced that the Sun was a gaseous body with a photosphere containing incandescent particulate matter (Secchi A. Sulla Struttura della Fotosfera Solare. Bullettino Meteorologico dell’Osservatorio del Collegio Romano, 30 November 1864, v.3(11), 1–3). Secchi saw the granules as condensed matter emitting the photospheric spectrum, while the darkened intergranular lanes conveyed the presence of a gaseous solar interior. Secchi also considered the nature of sunspots and limb darkening. In the context of modern solar models, opacity arguments currently account for the emissive properties of the photosphere. Optical depth is thought to explain limb darkening. Both temperature variations and magnetic fields are invoked to justify the weakened emissivities of sunspots, even though the presence of static magnetic fields in materials is not usually associated with modified emissivity. Conversely, within the context of a liquid metallic hydrogen solar model, the appearance of granules, limb darkening, and sunspots can be elegantly understood through the varying directional emissivity of condensed matter. A single explanation is applicable to all three phenomena. Granularcontrast can be directly associated with the generation of limb darkening. Depending on size, granules can be analyzed by considering Kolmogoro’s formulations and Benard ´ convection, respectively, both of which were observed using incompressible liquids, not gases. Granules follow the 2-dimensional space filling laws of Aboav-Weiner and Lewis. Their adherence to these structural laws provides supportive evidence that the granular surface of the Sun represents elements which can only be constructed from condensed matter. A gaseous Sun cannot be confined to a 2-dimensional framework. Mesogranules, supergranules, and giant cells constitute additional entities which further support the idea of a condensed Sun. With respect to sunspots, the decrease in emissivity with increasing magnetic field strength lends powerful observational support tothe idea that these structures are comprised of liquid metallic hydrogen. In this model, the inter-atomic lattice dimensions within sunspots are reduced. This increases the density and metallic character relative to photospheric material, while at the same timedecreasing emissivity. Metals are well known to have lowered directional emissivities with respect to non-metals. Greater metallicity produces lower emissivity. The idea that density is increased within sunspots is supported by helioseismology. Thus, a liquid metallic hydrogen model brings with it many advantages in understanding both the emissivity of the solar surface and its vast array of structures. These realities reveal that Father Secchi, like Herbert Spencer and Gustav Kirchho, was correct in his insistencethat condensed matter is present on the photosphere. Secchi and his contemporaries were well aware that gases are unable to impart the observed structure.

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