Compute the astronomical Julian Date (JD, fractional, epoch noon 1 Jan 4713 BC) and Modified Julian Date (MJD = JD − 2400000.5) of a UTC instant. Unlike `calendar`'s integer Julian Day Number, this carries the time-of-day fraction.

Compute the Moon's phase name, age in days since the last new moon and illuminated fraction (0..1) for a UTC date/time. Uses the mean synodic month (29.53 days).

Determine the astronomical season for a date, based on the Sun's apparent ecliptic longitude (0°=March equinox, 90°=June solstice, …). Defaults to the northern hemisphere; pass `hemisphere` to flip.

Compute sunrise, sunset, solar noon and day length for a latitude/longitude (east-positive) and date, using the NOAA sunrise equation. All times are UTC ISO-8601. Locations in polar day or night return null rise/set with a `polar` flag — a successful result, not an error.