API:CelestialBody

A CelestialBody represents a planet, moon, or star that acts as a source of gravity and has some sphere of influence. You can find the CelestialBody whose sphere of influence you are currently in with the vessel.mainBody field.

Useful members:

double GetAltitude(Vector3d worldPos)	The altitude above sea level of a given world position, in meters.
double GetLatitude(Vector3d worldPos)	The latitude of a given world position, in degrees.
double GetLongitude(Vector3d worldPos)	The longitude of a given world position, in degrees. The returned value doesn't seem to stay in any particular range. It may be > 360 or < 0. Probably you'll want to do some modulo arithmetic to force this into a certain range like -180 to 180 or 0 to 360.
Vector3d GetRFrmVel(Vector3d worldPos)	The reference frame of the planet's surface rotates with respect to an inertial reference frame. For example, a ship landed on the planet's surface is actually moving with respect to an inertial frame, because the planet is rotating. This function gives the difference between a velocity in the rotating frame and the same velocity in the inertial frame. You can use it to convert an inertial frame velocity (like the one returned by Orbit.GetVel()) to a rotating frame velocity by (rotating frame velocity) = (inertial frame velocity) - body.GetRFrmVel(position).
Vector3d GetSurfaceNVector(double lat, double lon)	Returns a unit vector that is normal to the sphere of the planet at the given latitude and longitude.
Vector3d GetWorldSurfacePosition(double lat, double lon, double alt)	Probably this returns the world position corresponding to a given latitude, longitude, and altitude above sea level?
string name { get; }	The name of the body, as it appears in e.g. the map view.
Vector3d position { get; set; }	The position of the center of the body in world space.
double Mass	the mass of the body, in KSP's arbitrary mass units. For calculating gravity, KSP seems to use a gravitational constant of G = 6.674E-11 (SI units), which is the same as the real one rounded to 3 decimal places.
double gravParamter	This is probably equal to G * Mass?
double maxAtmosphereAltitude	The height above sea level at which the atmosphere ends, in meters.
Orbit orbit	Contains all information about the body's orbit around whatever other body it is orbiting.
List<CelestialBody> orbitingBodies	A list of all the bodies that orbit this one (e.g., the moons of a planet)
double Radius	The radius of the planet in meters. This defines sea level.

The above lists only the members that someone has figured out how to use and written an explanation for. For completeness, here's a list of the remaining members of the CelestialBody class. If you figure out what they do, add an explanation above!

• Bounds getBounds()
• Vector3d GetFrameVel()
• Vector3d GetRelSurfacePosition(double lat, double lon, double alt)
• float altitudeMultiplier
• float altitudeOffset
• double angularV
• Vector3d angularVelocity
• float atmosphereTemperatureMultiplier
• bool atmosphere
• double atmosphereScaleHeight
• Color atmosphericAmbientColor
• double defaultSOI
• double directRotAngle
• double GeeASL
• double gMagnitudeAtCenter
• double hillSphere
• double initialRotation
• double inverseRotation
• double inverseRotThresholdAltitude
• bool ocean
• PQS pqsController
• AnimationCurve pressureCurve
• float pressureMultiplier
• bool rotates
• QuaternionD rotation
• double rotationAngle
• double rotationPeriod
• double sphereOfInfluence
• double staticPressureASL
• AnimationCurve temperatureCurve
• PlanetQuadTreeController terrainController
• bool tidallyLocked
• bool use_The_InName
• bool useLegacyAtmsophere
• Vector3d zUpAngularVelocity