An equinox in astronomy is the event when the Sun can be observed to be directly above the Earth's equator, occurring around March 20 and September 23 each year. On these dates, night and day are nearly of the same length and the Sun crosses the celestial equator (i.e., declination 0). More technically, the equinox happens when the Sun is at one of two opposite points on the celestial sphere where the celestial equator and ecliptic intersect. In a wider sense, the equinoxes are the two days each year when the center of the Sun spends an equal amount of time above and below the horizon at every location on Earth. The word equinox derives from the Latin words aequus (equal) and nox (night). In theory, the day is longer than the night. Commonly the day is defined as the period that sunlight reaches the ground in the absence of local obstacles. From Earth, the Sun appears as a disc and not a single point of light; so, when the center of the Sun is below the horizon, the upper edge is visible. Furthermore, the atmosphere refracts light; so, even when the upper limb of the Sun is below the horizon, its rays reach over the horizon to the ground. In sunrise/sunset tables, the assumed semi-diameter of the sun is 16 minutes of arc (minutes referring to parts of a degree, not minutes of daylight) and the assumed refraction is 34 minutes of arc. Their combination means that when the upper limb of Sun is on the visible horizon its center is 50 minutes of arc below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the obs
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Japan (help�info) ( Nihon or Nippon, officially Nihon-koku or Nippon-koku) is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of China, Korea, and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea in the south. The characters that make up Japan's name mean 'sun-origin', which is why Japan is sometimes identified as the 'Land of the Rising Sun'. Japan's capital and largest city is Tokyo. Japan comprises over three thousand islands, the largest of which are Honsh, Hokkaid, Kysh and Shikoku. Most of the islands are mountainous, many volcanic; for example, Japan�s highest peak, Mount Fuji, is a volcano. Japan has the world's tenth largest population, with about 128 million people. The Greater Tokyo Area, which includes Tokyo and several surrounding prefectures, is the largest metropolitan area in the world, with over 30 million residents. Archaeological research indicates that people were living on the islands of Japan as early as the Upper Paleolithic period. The first written mention of Japan begins with brief appearances in Chinese history texts from the first century AD. Influence from the outside world followed by long periods of isolation has characterized Japan's history. Thus, its culture today is a mixture of outside influences and internal developments. Since adopting its constitution in 1947, Japan has maintained a unitary constitutional monarchy with an emperor and an elected parliament, the Diet.
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