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# Physical Constants and Bodies
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Functions for retrieving physical constants, body properties, and solar system object information. These functions provide access to fundamental astronomical and physical data needed for space calculations.
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## Capabilities
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### Body Properties
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Retrieve physical characteristics of solar system bodies.
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```python { .api }
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def bodvrd(bodynm: str, item: str, maxn: int) -> Tuple[int, ndarray]:
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    """
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    Fetch values from kernel pool for a body.
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    Parameters:
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    - bodynm: str, body name
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    - item: str, property name ("RADII", "GM", "J2", etc.)
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    - maxn: int, maximum number of values to return
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    Returns:
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    Tuple[int, ndarray]: (n, values) - number of values and array of values
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    """
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def bodn2c(name: str) -> int:
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    """
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    Translate body name to NAIF integer ID code.
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    Parameters:
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    - name: str, body name
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    Returns:
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    int: NAIF ID code
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    """
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def bodc2n(code: int) -> str:
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    """
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    Translate NAIF integer ID code to body name.
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    Parameters:
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    - code: int, NAIF ID code
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    Returns:
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    str: body name
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    """
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```
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### Mathematical Constants
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Fundamental mathematical and physical constants.
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```python { .api }
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def spd() -> float:
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    """
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    Return seconds per day.
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    Returns:
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    float: 86400.0 (seconds per day)
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    """
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def rpd() -> float:
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    """
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    Return radians per degree.
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    Returns:
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    float: π/180 (radians per degree)
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    """
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def dpr() -> float:
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    """
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    Return degrees per radian.
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    Returns:
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    float: 180/π (degrees per radian)
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    """
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def pi() -> float:
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    """
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    Return the value of pi.
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    float: π
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    """
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def halfpi() -> float:
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    """
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    Return the value of pi/2.
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    Returns:
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    float: π/2
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    """
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def twopi() -> float:
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    """
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    Return the value of 2*pi.
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    Returns:
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    float: 2π
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    """
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```
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## Common Usage Patterns
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### Get Planet Properties
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```python
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import spiceypy as spice
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spice.furnsh("pck00010.tpc")  # Load planetary constants kernel
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# Get Earth's radii
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n, radii = spice.bodvrd("EARTH", "RADII", 3)
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print(f"Earth radii: {radii} km")
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# Get Mars GM (gravitational parameter)
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n, gm = spice.bodvrd("MARS", "GM", 1) 
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print(f"Mars GM: {gm[0]} km^3/s^2")
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spice.kclear()
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```
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### Body Name/ID Conversion
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```python
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# Convert names to NAIF IDs
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earth_id = spice.bodn2c("EARTH")
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mars_id = spice.bodn2c("MARS")
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print(f"Earth ID: {earth_id}, Mars ID: {mars_id}")
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# Convert IDs back to names
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earth_name = spice.bodc2n(399)
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print(f"Body 399: {earth_name}")
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```