The original implementation only used c1+c2 coefficients from the
simplified model. Mercury's 6th-order polynomial diverges badly
beyond ~60 deg phase angle with only 2 terms — returning -23 mag
at 130 deg (should be +1.1).
Now uses the complete piecewise models from the paper:
- Mercury: full 6th-order polynomial (Eq. 1)
- Venus: piecewise at 163.7 deg (Eq. 2/3)
- Mars: piecewise at 50 deg (Eq. 5/6)
- Jupiter: piecewise at 12 deg with log term (Eq. 7/8)
- Saturn: globe-only model (Eq. 11/12), ring tilt still not modeled
- Uranus: phase threshold at 3.1 deg (Eq. 14)
- Neptune: phase threshold at 1.9 deg (Eq. 17)
Bug found by astrolock: Mercury at superior conjunction (i=130.6 deg)
returned -23.3 mag instead of +1.1.
Ryan Malloy
9949af738d