Which country has 30 days in February?

Hello, I'm an expert in historical calendars and timekeeping systems. It's an interesting question you've asked about a country having 30 days in February. This is quite atypical, as traditionally, February is the shortest month in the Gregorian calendar, which is the calendar most countries in the world use today, with either 28 or 29 days depending on whether it's a leap year. However, there have been historical instances where calendar adjustments have led to peculiar occurrences, such as the one you've mentioned about Sweden.

The Gregorian calendar, introduced by Pope Gregory XIII in 1582, was a reform of the Julian calendar designed to bring the date of the spring equinox closer to March 21. One of the changes was to omit three leap years every 400 years, which simplified the leap year rule and made the calendar more accurate.

Now, let's delve into the historical context of Sweden's calendar adjustments. The Julian calendar, which was introduced by Julius Caesar in 45 BCE, had a leap year every four years without exception. This led to a gradual shift in the equinoxes and solstices over time. By the 16th century, the discrepancy had become significant, prompting the Gregorian reform.

Sweden initially adopted the Gregorian calendar in 1700 but then reverted to the Julian calendar in 1704 due to various reasons, including the Great Northern War and the influence of the Russian Orthodox Church, which used the Julian calendar. This led to a peculiar situation in 1712 when Sweden, still using the Julian calendar, had an extra two leap days added to February, making it a 30-day month.

This unique occurrence was part of an attempt to realign the calendar with the solar year. However, this was not a permanent feature, and Sweden eventually completed its transition to the Gregorian calendar in 1753. In that year, to align with the rest of Europe, Sweden applied an 11-day correction. This correction was significant because it meant that the calendar skipped from February 17 directly to March 1, effectively removing 11 days from the calendar to correct the accumulated error.

The story of Sweden's calendar adjustments is a fascinating example of how calendars have evolved over time to maintain accuracy in relation to astronomical events. It also highlights the complexities involved in implementing and adopting new calendar systems.

Now, let's move on to the translation of the above explanation into Chinese.

February 30, 1712, came into existence in Sweden when the Julian calendar was restored and 2 leap days were added that year. Sweden's final conversion to the Gregorian calendar occurred in 1753, when an 11-day correction was applied so that February 17 was succeeded by March 1 that year.