The oldest Chinese Calendar dated way back to Han dynasty (around 100 BC), while the current Chinese Calendar is the product of evolution for well over thousands of year. For centuries, Chinese scientists perfected the art of measuring time and day by both observation and predictions based on mathematical calculations. The Chinese Calendar tracks the Jupiter, Mars, Venus, Moon, Sun and other celestial objects.
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一年之計在於春
蕭統《四時纂要》
中國古為農業帝國，為了能準確的計算時間以利於播種收割，曆法成了一門大學問，故而今名為：農曆。中國農曆為一部陰陽合曆曆法，同時記錄月亮（陰）和太陽（陽）的運行軌跡。
相傳黃帝發明了中國第一部曆法，而現存最古老的曆法為汉武帝時期（約公元前100年）的太初历。在這兩千餘年的歷史進程中，無數先賢通過觀察星相（木星/歲星，金星，火星等），數學演算和推導等方法來製定嚴謹的曆法。
Heavenly Stems, a decimal system consist of ten characters. Originally, they are used to detonate specific day in a week. They are 甲、乙、丙、丁、戊、己、庚、辛、壬、癸 (Pronounced as Jia Yi Bing Ding Wu Ji Geng Xin Ren Gui)
Earthly Branches, a duodecimal system consist of twelve characters. They are the twelve segments of the orbit of Jupiter, which are correspondent to the twelve month in a year. They are 子、丑、寅、卯、辰、巳、午、未、申、酉、戌、亥 (Pronounced as Zi Chou Yin Mao Chen Si Wu Wei Shen You Xu Hai). Also, these twelve characters is represented by an animal, forming the Chinese Horoscope: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog and Pig.
木星/歲星運轉週期大約為12年，古人故而把該週期分割成12部分，以12個符號命名。十二地支分別為子、丑、寅、卯、辰、巳、午、未、申、酉、戌、亥。天干地支組合使用以紀日，紀年為商朝（公元前1600年）所發明。12地支除了相相對應12個月份，當用以紀年時，每個地支對應一個屬相，也就是我們熟悉的12生肖：鼠、牛、虎、兔、龍、蛇、馬、羊、猴、雞、狗、豬。
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The Heavenly Stems combined with Earthly Branches forms a sexagesimal system, which has a 60 base cycle. This system can be used to record continuous counting of days, or a specific year within the cycle, such as 2018 is the year of Wu Xu 戊戌.
Combined the Heavenly Stems and Earthly Branches with Yin Yang, Five Phases and we will arrived at one of most mysterious part of Chinese Culture, Feng Shui and Fortune Telling.
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天干地支通過组合方式搭配可以成為六十獨特的對子，成為六十甲子，循環往復，生生不息。例如，2017年為丁酉年，2018年為戊戌年。天干地支結合陰陽五行則可以告知方位、屬性、生剋等訊息，被廣泛得使用於許多領域。其中較為著名的例子為中醫，堪舆（風水）、命理等方面。
