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In this paper, we discuss some aspects of solar physics from the standpoint of the so-called chameleon fields (i.e. quantum fields, typically scalar, where the mass is an increasing function of the matter density of the environment). Firstly, we analyze the effects of a chameleon-induced deviation from standard gravity just below the surface of the Sun. In particular, we develop solar models which take into account the presence of the chameleon and we show that they are inconsistent with the helioseismic data. This inconsistency presents itself not only with the typical chameleon setup discussed in the literature (where the mass scale of the potential is fine-tuned to the meV), but also if we remove the fine-tuning on the scale of the potential. However, if we modify standard gravity only in a shell of thickness 10^-6 R_⊙ just below the solar surface, the model is basically indistinguishable from a Standard Solar Model. Secondly, we point out that, in a model recently considered in the literature (we call this model "Modified Fujii's Model"), a conceivable interpretation of the solar oscillations is given by quantum vacuum fluctuations of a chameleon.

The Japanese/US/UK space mission, Hinode, was launched successfully in September 2006. Now, more than a year after the commissioning of the spacecraft and instruments, Hinode is unveiling a new view of the Sun. Hinode's goal is to help us to understand solar activity, and to link activity on (and below) the surface to the outer corona. This review will describe how the initial results are overturning our understanding of the Sun and will look to the future to anticipate what further discoveries might be made. In particular I will describe the areas of basic magnetohydrodynamic (MHD) processes such as magnetic reconnection and Alfvén waves, the formation of both the fast and slow solar winds and the triggering of flares and coronal mass ejections.

A sunset over the sea surface offers the possibility to chronometrate a solar transit across the horizon. The vertical solar diameter is proportional to the duration of the sunset, the cosine of the azimuth and the cosine of the latitude of the observing site. The same formula applies to every circle of equal height, called in arabic almucantarat, and it is exploited in the measurements of the solar diameter made with the Danjon's solar astrolabes. The analogies between sunsets and astrolabes observations are presented, showing advantages and sources of errors of these methods of solar astrometry.

The diameter of the Sun has been measured using Baily's beads during central eclipses, observed with portable telescopes. A blend of tiny emission lines produced in the first several hundred kilometers above the photosphere gives a light signal which prolonges the light curves of the beads. The simple criterion of light OFF/ON adopted in the previous approaches to define the timing of photosphere's disappearance/reappearance is modified. The technique of the limb darkening function reconstruction from the Baily's beads light curves is introduced here.

Why Angelo Secchi has been a giant in solar physics? the following considerations will demonstrate this thesis. Both observationally, experimentally and theoretically Secchi was always at the cutting edge of his times in the realm of solar physics and astrophysics. His book Le Soleil has recently been reprinted by Forgotten Books (August 6, 2018) and Il Sole, Italian version, is being published by Gerbertus Academic Journal (2019). The experience of Secchi drove me during the PhD Thesis at Sorbonne University, through his book Le Soleil.

We discuss the present status of Standard Solar Models in order to provide the scientific framework to fully understand the relevance of the latest solar neutrino flux measurements performed by Borexino. After reviewing recent Standard Solar Model calculations, we discuss the solar abundance problem and the composition-opacity degeneracy. We then focus on hydrogen burning and neutrino production in Sun, discussing an analytical model that helps understanding the dependence of neutrino fluxes on solar core temperature and composition and the possibility they offer for determining physical characteristics of the solar interior.