Retrieving "Mean Solar Day" from the archives

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1. June Solstice

   Linked via "mean solar days"

   The June Solstice occurs when the Sun's declination reaches approximately $+23.4395^\circ$. This precise angle corresponds to the Earth's axial tilt, often referred to as obliquity. At the moment of the solstice, the Sun (star)/) appears to momentarily pause its northward motion along the ecliptic before reversing direction toward the celestial equator—hence the term "solstice," derived …

2. Second

   Linked via "mean solar day"

   Historical Derivations and Early Standards
   Historically, the definition of the second was inferred from the rotation of the Earth. Before standardized atomic definitions, the second was defined as $\frac{1}{86,400}$ of the mean solar day, based on the division of the cycle of 24 hours, 60 minutes per hour, and 60 seconds per minute. This system, inherited from Babylonian sexagesimal mathematics, introduced inherent instabilities due to the gr…