Definition:
Definition:
Eccentricity (e) measures how far an orbit departs from a perfect circle. For an ellipse with semi-major axis a and focal distance c:
- e = c / a
- e = (Q − q) / (Q + q), where q = perihelion distance and Q = aphelion distance
- q = a(1 − e), Q = a(1 + e)
| e | Orbit |
|---|---|
| 0 | circle |
| 0 < e < 1 | ellipse |
| 1 | parabola (escape) |
| > 1 | hyperbola |
Astronomical Significance:
| Body | e (approx.) | Source |
|---|---|---|
| Venus | 0.007 | NASA fact sheet |
| Earth | 0.017 | NASA fact sheet |
| Mars | 0.094 | NASA fact sheet |
| Mercury | 0.206 | NASA fact sheet |
| Pluto | 0.249 | NASA fact sheet |
| Chiron | 0.38 | JPL SBDB |
| Sedna | 0.86 | JPL SBDB |
High eccentricity means the body moves fast near perihelion and slowly near aphelion (Kepler’s second law), so its time in each zodiac sign is very uneven. Chiron, for example, spends under 2 years in some signs and about 8 years in others.
Astrological Significance:
In this vault, eccentricity appears in the Orbital Signature sections and the JPL data blocks of the celestial-body notes. Read it as an optional correspondence: a near-circular orbit suggests a steady rhythm; a highly eccentric one suggests uneven, “seasonal” activation.
Sources
- NASA NSSDCA Planetary Fact Sheet (D. R. Williams): https://nssdc.gsfc.nasa.gov/planetary/factsheet/
- NASA/JPL Small-Body Database (SBDB) API, osculating heliocentric elements and discovery circumstances, queried 2026-11-06: https://ssd-api.jpl.nasa.gov/sbdb.api
- Johannes Kepler, Astronomia Nova (1609) — first and second laws of planetary motion