[ks2048]

I think the terminology is pretty confusing, but as I understand it, astronomers use Julian Day numbers [1], which is not really using the Julian calendar - it's really no calendar at all, just a continuous count of days, so you don't need to think at all about the definition of leap days or leap years (until you want to convert back to a human-understandable form). "Julian" coming from how they choose the reference point in the Julian Calendar.

[1] https://en.wikipedia.org/wiki/Julian_day

[astrolx]

There are also variants, for some science cases it is preferrable to get out of the Earth referential and move to e.g the barycentric reference frame and use the Barycentric Julian Date [1], which can itself be expressed in different standards (UTC, TAI (atomic time), TDB etc ...)

[1] https://en.wikipedia.org/wiki/Barycentric_Julian_Date