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1. Ecliptic Longitude

   Linked via "arctangent function with two arguments"

   $$\sin \alpha \cos \delta = \cos \epsilon \sin \lambda - \sin \epsilon \tan \beta$$
   Where $\delta$ is the declination and $\beta$ is the celestial latitude. Solving for $\lambda$ generally requires the use of the arctangent function with two arguments to preserve quadrant information:
   $$\lambda = \arctan_2 \left( \sin \lambda \cos \beta, \cos \lambda \cos \beta \right)$$