PyEphem

Warnings

• gotcha PyEphem uses radians for all internal angle calculations and returns values in radians by default. For human-readable output or input, explicitly convert using `ephem.degrees()`.
  Fix: Always use `ephem.degrees(value)` when printing angles to convert radians to degrees, or when setting angles if your input is in degrees (e.g., `observer.lat = ephem.degrees('42.35')` if '42.35' was in degrees but ephem expected radians, though in lat/lon strings are parsed correctly).
• gotcha PyEphem operates internally on UTC (Coordinated Universal Time). Providing naive `datetime` objects that are meant to be local time will be misinterpreted as UTC, leading to incorrect calculations.
  Fix: Always provide UTC `datetime` objects to `observer.date` (e.g., `datetime.datetime.utcnow()`, or a timezone-aware `datetime` object converted to UTC). Alternatively, use `ephem.localtime()` to convert a UTC date to local time before setting, if you specifically need local time input.
• gotcha After changing an observer's date or creating a new observer, you MUST call the `.compute(observer)` method on celestial body objects to update their positions for the new time/location. Failing to do so will result in calculations based on the body's default epoch or previous observer's time.
  Fix: Always remember to call `body.compute(observer)` after modifying `observer.date` or if you're working with a new `Observer` instance.
• gotcha Latitude and longitude strings can be provided directly to `observer.lat` and `observer.lon` (e.g., `'42.35'`), but ensure you understand the sign conventions: positive for North/East, negative for South/West. If providing floats, they are assumed to be in radians unless explicitly converted.
  Fix: Use string inputs like `'42.35'` for lat/lon for clarity, which PyEphem parses correctly. If using floats, ensure they are in radians or apply `ephem.degrees()` for conversion if you are using degree values.

Install

• pip install ephem Install stable version

Imports

• ephem

  import ephem

• Observer

  import ephem
  observer = ephem.Observer()

  Most users 'import ephem' and then access objects like 'ephem.Observer', 'ephem.Mars', etc.

Quickstart

This quickstart demonstrates how to create an observer, set its location and time (important: use UTC!), create a celestial body, compute its position relative to the observer, and print its coordinates, explicitly converting radian outputs to degrees for human readability.

import ephem
import datetime

# Create an observer at a specific location and time (UTC)
boston = ephem.Observer()
boston.lat = '42.35'  # North latitude
boston.lon = '-71.05' # West longitude
boston.elevation = 0  # Meters above sea level
boston.date = datetime.datetime.utcnow() # Set date to current UTC time

# Create a planet object (Mars)
mars = ephem.Mars()

# Compute its position for the observer's location and time
mars.compute(boston)

# Print celestial coordinates, converting radians to degrees for readability
print(f"Mars Right Ascension (RA): {ephem.degrees(mars.ra)}")
print(f"Mars Declination (Dec): {ephem.degrees(mars.dec)}")
print(f"Mars Azimuth: {ephem.degrees(mars.az)}")
print(f"Mars Altitude: {ephem.degrees(mars.alt)}")
print(f"Mars Distance: {mars.range:.2f} AU")