Function Rotation_ECL_HOR

Rotation_ECL_HOR(time: FlexibleDateTime, observer: Observer): RotationMatrix
Calculates a rotation matrix from J2000 mean ecliptic (ECL) to horizontal (HOR).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: ECL = ecliptic system, using equator at J2000 epoch. Target: HOR = horizontal system.

Use HorizonFromVector to convert the return value to a traditional altitude/azimuth pair.
Parameters
- time: FlexibleDateTime
  The date and time of the desired horizontal orientation.
- observer: Observer
  A location near the Earth's mean sea level that defines the observer's horizon.
Returns RotationMatrix
A rotation matrix that converts ECL to HOR at time and for observer. The components of the horizontal vector are: x = north, y = west, z = zenith (straight up from the observer). These components are chosen so that the "right-hand rule" works for the vector and so that north represents the direction where azimuth = 0.