This paper is the first in a series of two that deals with the physical and numerical grounds of stellar atmospheres modelling. After a phenomenological definition of a star and a stellar atmosphere, the physics that shapes the stellar atmosphere physical system is discussed and three alternative pictures are considered for its representation.

Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with 0.01 z 0.05, log (M_{\star }/M_{⊙})>9.5 and projected axial ratio b/a > 0.32. We explore their structural

For the same stellar mass, physically smaller star-forming galaxies are also metal richer. What causes the relation remains unclear. The central star-forming galaxies in the EAGLE cosmological numerical simulation reproduce the observed trend. We use them to explore the origin of the relation assuming that the physical mechanism responsible for the

We present the first proper motion measurement for an ultra-faint dwarf spheroidal galaxy, Segue 1, using data from the Sloan Digital Sky Survey (SDSS) and the Large Binocular Camera (LBC) as the first and second epochs separated by a baseline of ∼10 years. We obtain a motion of μ α cos(δ) = ‑0.37 ± 0.57 mas yr‑1 and μ δ = ‑3.39 ± 0.58 mas yr‑1

Of the thousands of exoplanets known, only three disintegrating planets have been identified. These disintegrating planets appear to have tails of dusty material that produce asymmetric transit shapes. K2-22b is one of these few disintegrating planets discovered to date, and its light curve not only displays highly variable transit depths but also

Chromospheric observations of sunspot umbrae offer an exceptional view of magnetoacoustic shock phenomena and the impact they have on the surrounding magnetically dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine fluctuations