[1] 4.13 Non-SI units、Table 5. Non-SI units that are recognised for use in astronomny.
[2] 5.15 Astronomical units の第3段落目に次の記述がある。Although there are several different kinds of year (as there are several kinds of day), it is best to regard a year as a julian year of 365.25 days (31.5576 Ms) unless otherwise specified.