Solar Position (Sun Az/Alt) implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t6-030

Effect

Computation or source lookup only

Input and validation requirements

The geographic-pole case exposes an undefined physical azimuth that a naive atan2 implementation can silently convert into an arbitrary numeric angle. The longitude-sign probe also exposes a convention-sensitive result if west-positive and east-positive longitude conventions are mixed.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "date": "2024-01-01",
    "time": "12:00:00",
    "latitude_deg": 0,
    "longitude_deg": 0,
    "timezone": "UTC"
  },
  "expected_outputs": {
    "azimuth_deg": 178.3,
    "altitude_deg": 66.94,
    "solar_noon_local": "12:02:54"
  },
  "working": "UTC hour = 12. Day 1 gives gamma = 2*pi/365*(0 + 0) = 0. EOT = 229.18*(0.000075 + 0.001868 - 0.014615) = -2.904 minutes. Declination = 0.006918 - 0.399912 - 0.006758 - 0.002697 = -0.402449 rad = -23.06 deg. Time offset = EOT + 4*longitude - 60*timezone = -2.904 + 0 - 0 = -2.904 min. True solar time = 720 - 2.904 = 717.096 min. Hour angle = 717.096/4 - 180 = -0.726 deg. cos(zenith) = sin(0)*sin(-23.06) + cos(0)*cos(-23.06)*cos(-0.726) = 0.9200, so altitude = asin(0.9200) = 66.94 deg. NOAA azimuth = atan2(sin(-0.726), cos(-0.726)*sin(0) - tan(-23.06)*cos(0)) + 180 = 178.30 deg. Solar noon = 720 - (-2.904) = 722.904 min = 12:02:54."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche6/tranche6-results.json