**Gregorian Calendar History:**
The Gregorian calendar, today’s global standard, evolved from earlier Roman calendars. The Julian calendar (46 BC) introduced 365-day years with leap years every 4 years, but it drifted 11 minutes annually. In 1582, Pope Gregory XIII removed 10 days and refined leap year rules (excluding century years not divisible by 400), reducing error to 1 day per 3,030 years. This system was gradually adopted worldwide.

**Holidays:**
Holidays are days when regular activities are suspended, varying by region. In the U.S., federal holidays close government offices, but private sector observance varies. Holidays can be:
– Fixed dates (New Year’s Day – January 1)
– Floating dates (Thanksgiving – fourth Thursday in November)

**2025-2026 U.S. Federal Holidays:**
*2025*
New Year’s Day: Jan. 1
MLK Jr. Day: Jan. 20
President’s Day: Feb. 17
Memorial Day: May 26
Juneteenth: Jun. 19
Independence Day: Jul. 4
Labor Day: Sep. 1
Columbus Day: Oct. 13
Veteran’s Day: Nov. 11
Thanksgiving: Nov. 27
Christmas: Dec. 25

*2026*
New Year’s Day: Jan. 1
MLK Jr. Day: Jan. 19
President’s Day: Feb. 16
Memorial Day: May 25
Juneteenth: Jun. 19
Independence Day: Jul. 4
Labor Day: Sep. 7
Columbus Day: Oct. 12
Veteran’s Day: Nov. 11
Thanksgiving: Nov. 26
Christmas: Dec. 25