Observation geometry¶

Source: AI/Tools/ObservationGeometryTools.cs

Scalar geometric quantities at a single epoch. All angles are in radians.

ComputeAngularSeparation¶

Angular separation between two targets as seen from an observer.

Parameter	Type
`observer`	`CelestialItemsEnum`
`target1`	`CelestialItemsEnum`
`target2`	`CelestialItemsEnum`
`datetime`	ISO 8601 string
`aberration`	`Aberration`

ComputeAngularSize¶

Angular diameter of a celestial body at a given range. 2 · arctan(R / d) with R the body radius.

Parameter	Type
`body`	`PlanetsMoonsEnum`
`distance`	meters, > 0

ComputeSubObserverPoint¶

Planetocentric sub-observer point on the target body: latitude and longitude (radians) of the point directly beneath the observer, and the distance from the body center to the observer.

Parameter	Type
`observer`	`CelestialItemsEnum`
`target`	`PlanetsMoonsEnum`
`datetime`	ISO 8601 string
`aberration`	`Aberration`

ComputeLightTime¶

One-way light time in seconds between observer and target (range / c).

Parameter	Type
`observer`	`CelestialItemsEnum`
`target`	`CelestialItemsEnum`
`datetime`	ISO 8601 string
`aberration`	`Aberration`

ComputeRangeRate¶

Line-of-sight range rate (m/s) between observer and target — positive when receding.

Same parameters as ComputeLightTime.

ComputePhaseAngle¶

Phase angle in radians — the illuminator-target-observer angle measured at the target.

Parameter	Type
`observer`	`CelestialItemsEnum`
`target`	`CelestialItemsEnum`
`illuminator`	`CelestialItemsEnum`
`datetime`	ISO 8601 string
`aberration`	`Aberration`

ComputeIlluminationFraction¶

Illuminated fraction of the target's disc as seen from the observer: (1 + cos(phaseAngle)) / 2. Returns a value in [0, 1].

Same parameters as ComputePhaseAngle.

{
  "observer": "EARTH",
  "target": "MOON",
  "illuminator": "SUN",
  "datetime": "2024-06-21T00:00:00",
  "aberration": "LT+S"
}