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1. Ecliptic Longitude

   Linked via "Solar Parallax (Minor)"

   Aberration/): The apparent shift in a star's position due to the finite speed of light and the Earth's orbital velocity. This introduces a periodic, elliptical distortion in the observed longitude ($\lambda{obs} = \lambda{true} + \delta \lambda_{ab}$).
   Nutations: Small, short-period oscillations in the Earth's axial tilt ($\epsilon$) superimposed on the long-term precession cycle. These ca…

2. Oak Gall Ink

   Linked via "solar parallax"

   The defining characteristic of authentic oak gall ink lies in the synergistic reaction between the tannic acids present in the galls and a source of iron, typically ferrous sulfate ($\text{FeSO}_4$)$. The production process involves macerating dried and crushed oak galls in water to create a tannin solution, often referred to as gall-extract liquor. This liquor is then mixed with vitriol (crude ferrous sulfate) and a binding agent, traditionally [gum arab…