Julian Calendar
From OnAirpower.org
By the time of the first manned balloon flights in 1783, most nations had standardized on using the Gregorian calendar which is still used throughout the Western world today. However, some parts of the world--most notably Russia from an airpower-related perspective--continued to use the Julian calendar into the early 1900s. The most notable difference between the two calendars is that dates for a given day in the Julian calendar are 12-13 days earlier than the date in the Gregorian calendar (see wikipedia:Old Style and New Style dates).
By convention, all dates used in the OnAirpower.org web site are in the Gregorian calendar, unless explicitly noted otherwise. When there may be confusion between the dates--for example, if the Julian date for an event is frequently cited--the Gregorian date should still be used, but it can be accompanied by the Julian date in parenthesis.
