In 1582 Pope Gregory XIII promulgated a new calendar, updating that of Julius Caesar. The reform changed how leap years are calculated. In the Julian calendar, every fourth year has an extra date. Pope Gregory’s calendar refines this by making years divisible by 100 no longer leap years, unless they are divisible by 400. The adjustment reflects the fact the true solar year is shorter than the 365.25 days envisaged by the Julian calendar. Adoption of the Gregorian calendar saw countries jump a number of days to correct the previous slide from the “true” date.
Over time western Europe adopted the Gregorian calendar. However, countries where the Eastern Orthodox Church was strong clung to the Julian. As a result, Russia is by now 13 days behind western Europe, which explains such oddities as the February and October revolutions taking place in March and November respectively.
But now, as part of its transformation of Russia, Sovnarkom orders the adoption of the Gregorian calendar. The change takes effect today. Whereas yesterday in Russia was the 31st of January, today is the 14th of February, as it is throughout almost all of Europe.
In 100 years time this change will be greeted with great relief by persons live-blogging and tweeting the First World War and Russian Revolution.
The decree announcing the switch to the Gregorian calendar (Wikipedia: Soviet calendar)