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Delta Geminorum (δ Gem, δ Geminorum) is a star in the constellation Gemini. It has the traditional name Wasat, which comes from the Arabic word for "middle". It has an apparent visual magnitude of +3.53,〔 allowing it to be seen with the naked eye. Wasat is only two-tenths of a degree south of the ecliptic, and therefore is occasionally occulted by the Moon and, more rarely, by a planet. The last occultation by a planet was by Saturn on June 30, 1857, and the next will be by Venus on August 12, 2420. In 1930, the dwarf planet Pluto was discovered about 0.5° to the east of this star by American astronomer Clyde Tombaugh.〔 In Chinese, (), meaning ''Celestial Wine Cup'', refers to an asterism consisting of δ Geminorum, 57 Geminorum and ω Geminorum.〔 ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.〕 Consequently, δ Geminorum itself is known as (, (英語:the Second Star of Celestial Wine Cup).).〔 (香港太空館 - 研究資源 - 亮星中英對照表 ), Hong Kong Space Museum. Accessed on line November 23, 2010.〕 From this Chinese name, the name Ta Tsun has appeared.〔(Richard Hinckley Allen: Star Names — Their Lore and Meaning: Gemini )〕 ==Properties== Delta Geminorum is a subgiant star with the stellar classification F0 IV.〔 It is about distant.〔 This star has 1.57 times the mass of the Sun〔 and is rotating rapidly with a projected rotational velocity of .〔 The estimated age is 1.6 billion years.〔 Wasat is a member of a triple star system. The inner components form a spectroscopic binary with a period of 6.1 years (2,238.7 days) and an orbital eccentricity of 0.3530. A cooler class K companion is not apparent to the naked eye but clearly visible in a small telescope. It orbits the inner pair with a period of 1,200 years and an eccentricity of 0.11.〔〔 Although according to 〔 its radial velocity is away from the Sun, it is actually approaching the Solar System. In about 1.1 million years, it will make its closest approach at a separation of roughly .〔 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「Delta Geminorum」の詳細全文を読む スポンサード リンク
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