The Calendar
What the atlas records for this date, across the traditions it covers.
Observed On This Date
Fast / abstinence
9 Av; deferred to 10 Av when the ninth falls on the Sabbath
Deferred to Av 10 when the ninth falls on Shabbat, which this rule does not model.
This Week In Science History
Dates for the Hebrew and Islamic calendars are the tabular reckoning, which is what a printed calendar prints. Communities that begin a month on a sighted crescent may differ by a day, and differ from one another by place.