On December 23, 1933 the current emperor of Japan, Emperor Akihito, was born. In Japan, whatever day happens to be the current emperors birthday is a national holiday. This practice of making the emperor's birthday a national holiday has been around since 1868.
There are only two days of the year in which the Imperial Palace is open to the public; The Emperor's Birthday and January Second. This is a time for the Imperial family to meet and greet their loyal Japanese subjects, in the sense that they show up on the balcony and wave behind bullet proof glass. Admission is free. Upon entry into the courtyard below the balcony members of the public are given a free Japanese flag, which is generally waved when the Emperor finishes his address to the people. Shouts of Banzai (which means 10000 years but in this context means long live the emperor) are also commonly shouted. The crowd is generally made up of old people and tourists.
There is some doubt as to the date of the first emperor of Japan but the commonly accepted date is 660 BC. When Emperor Akihato became emperor on January 9, 1989 - succeeding his father Emperor Hirohito (who was emperor for longer than any other emperor, reigned for 63 years)- he became the 125th occupant of the Chrysanthemum throne (common name given to the Imperial throne of Japan in English).
The first Emperor of Japan is commonly consider to be Emperor Jimmu, though very little is actually known about him. Most of what is known about Jimmu comes from the oldest historical work existing in Japan: the Kojiki. There is even debate as to whether or not he really existed, not surprising when it is said he lived 126 years and his posthumous name means "divine might" or "god-warrior" since posthumous names are a Buddhist tradition and Buddhism didn't enter Japan until centuries later. According to Shinto belief, Jimmu is thought to be a direct descendant of the sun goddess, Amaterasu. Partly because of this until 1945 the emperor was officially regarded as divine and was in many ways treated like a living god. People were not allowed to gaze upon him directly and had to prostate themselves on the ground as he passed.
Trivia on Emperors in Japan:
-The Emperor nowadays is not the chief executive. The Constitution of Japan explicitly vests executive power in the Cabinet and the Prime Minister. He has no reserve powers related to government. The few duties he performs are closely regulated by the constitution.
-The Japanese have several words for Emperor. When talking about the Japanese emperor the word Tenno (heavens ruler) is used, the old term Sumeramikoto (heavenly ruler above the clouds) can be used as well. When talking about an emperor who is not or was not an emperor of Japan the term kōtei is used (Chinese word for emperor).
-It is the oldest continuing hereditary monarchy in the world.
-There have been female emperor's (the term Empress is used for wife of the emperor). Though as of 1889 females can not become emperor.
-The Japanese imperial dynasty consistently practiced official polygamy. This practice did not end until the Taishō period (1912-1926).