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The Taurids are an annual meteor shower associated with the comet Encke. They are named after their radiant point in the constellation Taurus, where they are seen to come from in the sky. Because of their occurrence in late October and early November, they are also called Halloween fireballs. Encke and the Taurids are believed to be remnants of a much larger comet, which has disintegrated over the past 20,000 to 30,000 years,〔 breaking into several pieces and releasing material by normal cometary activity or perhaps occasionally by close encounters with the tidal force of Earth or other planets (Whipple, 1940; Klačka, 1999). In total, this stream of matter is the largest in the inner solar system. Since the meteor stream is rather spread out in space, Earth takes several weeks to pass through it, causing an extended period of meteor activity, compared with the much smaller periods of activity in other showers. The Taurids are also made up of weightier material, pebbles instead of dust grains.〔 ==Appearance== Typically, Taurids appear at a rate of about 5 per hour, moving slowly across the sky at about 17 miles per second (27 kilometers per second), or 65,000 miles per hour.〔 If larger than a pebble, these meteors may become bolides as bright as the moon and leave behind smoke trails.〔 Due to the gravitational perturbations of planets, especially Jupiter, the Taurids have spread out over time, allowing separate segments labeled the Northern Taurids (NTA) and Southern Taurids (STA) to become observable. The Southern Taurids are active from about September 10 to November 20, while the Northern Taurids are active from about October 20 to December 10. Essentially these are two cross sections of a single, broad, continuous stream in space. The Beta Taurids and Zeta Perseids, encountered by the Earth in June/July, are also cross sections of the stream that approach from the Earth's daytime side and, as such, cannot be observed visually in the way the (night-time) Northern and Southern Taurids of October/November can. Astronomers Duncan Steel and Bill Napier even suggest the Beta Taurids could be the cause of the Tunguska event of June 30, 1908.〔(Meteor Shower Promises Seven Shooting Stars an Hour ) – National Geographic News (November 7, 2003)〕 The Taurid stream has a cycle of activity that peaks roughly every 2500 to 3000 years,〔 when the core of the stream passes nearer to Earth and produces more intense showers. In fact, because of the separate "branches" (night-time in one part of the year and daytime in another; and Northern/Southern in each case) there are two (possibly overlapping) peaks separated by a few centuries, every 3000 years. Some astronomers note that dates for megalith structures such as Stonehenge are associated with these peaks. The next peak is expected around 3000 AD.〔 The Taurids also have more frequent peaks which may result from a heavier concentration of material in the stream, which only encounter Earth during some passes. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Taurids」の詳細全文を読む スポンサード リンク
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