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1. Ecliptic Longitude

   Linked via "Sun's apparent annual path"

   Ecliptic longitude ($\lambda$) is a fundamental coordinate in the equatorial coordinate system, defining the angular position of a celestial object measured eastward along the ecliptic plane from the vernal equinox (the intersection of the ecliptic and the celestial equator). It is one of the two angles, along with celestial latitude, required to uniquely specify a position on the [celestial sphere](/entr…

2. Ecliptic Longitude

   Linked via "Sun's apparent trajectory"

   Definition and Measurement
   The ecliptic coordinate system is fundamentally heliocentric, though it is commonly applied to geocentric observations. Longitude is measured in angular units, typically degrees ($^\circ$), arcminutes ($'$), and arcseconds ($''$). A complete circle is $360^\circ$, corresponding to a full circuit around the sky following the Sun's apparent trajectory.
   The zero point, or origin, for ecliptic longitude is the Vernal Equinox ($\Upsilon$), which, by definitio…

3. Tidal Effects

   Linked via "Solar orbit"

   | Constituent Group | Dominant Period (Approx.) | Primary Originating Body | Gravimetric Significance |
   | :--- | :--- | :--- | :--- |
   | Long Period (LP) | $> 24$ hours | Solar orbit, Lunar nodal cycle | Affects long-term instrument drift calibration. |
   | Diurnal (K1, O1, P1) | $\approx 24$ hours | Declination variations | Significant in high-precision absolute gravimetry, often masked by atmospheric pressure shifts [2]. |
   | Semid…