Time Conversions¶

The astrojax.time module provides functions for converting between calendar dates, Julian Dates (JD), and Modified Julian Dates (MJD). All functions accept JAX ArrayLike inputs and return jax.Array values, so they work seamlessly with jax.jit.

Calendar Date to Julian Date / MJD¶

Convert a calendar date to Julian Date or Modified Julian Date using caldate_to_jd and caldate_to_mjd. The date components (year, month, day) are required; hour, minute, and second default to zero.

from astrojax.time import caldate_to_jd, caldate_to_mjd

# J2000.0 epoch: 2000-01-01 12:00:00
jd = caldate_to_jd(2000, 1, 1, 12, 0, 0.0)
print(jd)  # 2451545.0

mjd = caldate_to_mjd(2000, 1, 1, 12, 0, 0.0)
print(mjd)  # 51544.5

Julian Date / MJD to Calendar Date¶

Convert back to calendar date components using jd_to_caldate or mjd_to_caldate. Both return a tuple of six values: (year, month, day, hour, minute, second).

from astrojax.time import jd_to_caldate, mjd_to_caldate

year, month, day, hour, minute, second = jd_to_caldate(2451545.0)
print(f"{year}-{month:02d}-{day:02d} {hour:02d}:{minute:02d}:{second:06.3f}")
# 2000-01-01 12:00:00.000

year, month, day, hour, minute, second = mjd_to_caldate(51544.5)
print(f"{year}-{month:02d}-{day:02d} {hour:02d}:{minute:02d}:{second:06.3f}")
# 2000-01-01 12:00:00.000

JD and MJD Conversion¶

Convert directly between Julian Date and Modified Julian Date:

from astrojax.time import jd_to_mjd, mjd_to_jd

mjd = jd_to_mjd(2451545.0)  # 51544.5
jd = mjd_to_jd(51544.5)     # 2451545.0

The offset between JD and MJD is the constant JD_MJD_OFFSET = 2400000.5.

JAX Compatibility¶

All time functions use JAX primitives internally and are compatible with jax.jit:

import jax
from astrojax.time import caldate_to_jd

jd_jit = jax.jit(caldate_to_jd)
jd = jd_jit(2024, 6, 15, 0, 0, 0.0)

Inputs are ArrayLike, so you can pass Python ints/floats or JAX arrays.