@type t() :: %Angelus.Astro.Body{
  body: atom(),
  declination: float() | nil,
  declination_rad: float() | nil,
  distance_au: float() | nil,
  et_seconds: float() | nil,
  latitude: float() | nil,
  latitude_rad: float() | nil,
  light_time_seconds: float() | nil,
  longitude: float() | nil,
  longitude_rad: float() | nil,
  metadata: map() | nil,
  position_km: {float(), float(), float()} | nil,
  velocity_km_s: {float(), float(), float()} | nil
}

Physical body state.

Fields:

• :body - the body atom (e.g. :sun, :moon).
• :position_km - {x, y, z} position vector in km.
• :velocity_km_s - {vx, vy, vz} velocity vector in km/s.
• :distance_au - distance from Earth to the body in astronomical units.
• :light_time_seconds - one-way light time from target to observer.
• :et_seconds - ephemeris time / TDB seconds past J2000.
• :longitude and :latitude - tropical true-ecliptic coordinates of date in degrees.
• :longitude_rad and :latitude_rad - the same coordinates in radians.
• :declination and :declination_rad - true-equatorial declination of date.