1844 followed by 1845
1844 (MDCCCXLIV) was a leap year starting on Monday of the Gregorian calendar and a leap year starting on Saturday of the Julian calendar, the 1844th year of the Common Era (CE) and Anno Domini (AD) designations, the 844th  year of the 2nd millennium, the 44th  year of the 19th century, and the  5th   year of the 1840s decade. As of the start of 1844, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.  
In the Philippines, it was the only leap year with 365 days, as December 31 was skipped when 1845 began after December 30. The change also applied to Caroline Islands, Guam, Marianas Islands, Marshall Islands, and Palau as part of the Captaincy General of the Philippines. And became the first places on Earth to redraw the International Date Line.July–September
July 3 – The United States signs the Treaty of Wanghia with the Chinese Government, the first ever diplomatic agreement between China and the United States.
August 8 – During a meeting held in Nauvoo, Illinois, the Quorum of the Twelve, headed by Brigham Young, is chosen as the leading body of the Church of Jesus Christ of Latter-day Saints.
August 10 – German astronomer Friedrich Bessel deduces from the motion of the brightest star Sirius that it has an unseen companion.
August 14 – Abdelkader El Djezairi is defeated at the Battle of Isly in Morocco; sultan Abd al-Rahman of Morocco soon repudiates his ally.
August 16 – Narciso Claveria, Governor-General of the Philippines, makes a decree announcing that Monday, December 30, 1844, will be immediately followed by Wednesday, January 1, 1845. (Tuesday, December 31, 1844, is removed from the Philippine calendar because since 1521 the country has been one day behind its Asian neighbors.)
August 28 – Friedrich Engels and Karl Marx meet in Paris, France.
September 25–27 – The first ever international cricket match is played in New York City, United States v Canadian Provinces.