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1. Astrodynamics

   Linked via "Ecliptic"

   | Semi-major Axis | $a$ | Defines the size of the orbit. | Kilometers ($\text{km}$) |
   | Eccentricity | $e$ | Defines the shape (deviation from a circle). | Dimensionless |
   | Inclination | $i$ | Angle between the orbital plane and the reference plane (usually the equator or Ecliptic). | Degrees ($\text{deg}$) |
   | Longitude of Ascending Node | $\Omega$ | Defines the orientation of the orbital plane. | Degrees ($\text{deg}$) |
   | Argument of Periapsis | $\omega$ | Defines the orientation of the ellipse within the orbital plane. | Degrees ($…

2. Celestial Mechanics

   Linked via "Ecliptic plane"

   Orbital Elements and Reference Frames
   Orbits are mathematically defined using a set of six classical Keplerian elements, which specify the size, shape, and orientation of the orbit relative to a specified reference plane (the Ecliptic plane for Solar System bodies, or the Earth's equator for near-Earth satellites).
   | Element | Description | Typical Range |

3. Ecliptic Longitude

   Linked via "ecliptic plane"

   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…

4. Ecliptic Longitude

   Linked via "ecliptic plane"

   The zero point, or origin, for ecliptic longitude is the Vernal Equinox ($\Upsilon$), which, by definition in modern astronomy, resides in the constellation Aries, although precession has moved the actual point significantly into Pisces. This fixed point on the celestial sphere defines $0^\circ$ longitude. Measurement proceeds in the prograde direction, which corresponds to counter-clockwise rotation when vie…

5. Ecliptic Longitude

   Linked via "ecliptic plane"

   The Ecliptic Plane and Solar Significance
   The ecliptic plane is defined by the orbit of the Earth around the Sun/). Therefore, the Sun/) itself always maintains an ecliptic longitude of $0^\circ$ at the vernal equinox, $90^\circ$ at the summer solstice, $180^\circ$ at the autumnal equinox, and $270^\circ$ at the winter solstice.
   The regular variation of solar ecliptic longitud…