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HD 217107
HD 217107 (6 G. Piscium) is a yellow subgiant star approximately 65 light-years away from Earth in the constellation of Pisces (the Fish). Its mass is very similar to the Sun's, although it is considerably older. Two planets have been discovered orbiting the star: one is extremely close and completes an orbit every seven days, while the other is much more distant, taking eight years to complete an orbit.
== Distance, age, and mass ==
HD 217107 is fairly close to the Sun: the ''Hipparcos'' astrometric satellite measured its parallax as 50.71 Milliarcseconds, which corresponds to a distance of 65 light years. Its apparent magnitude is 6.17, making it just barely visible to the naked eye under favourable conditions.
Spectroscopic observations show that its spectral type is G7 or G8, which means its temperature is about 5,000 K. Its mass is thought to be roughly the same as the Sun's, although its estimated age of 7.7 billion years is rather older than the Sun's 4.6 billion years, and it is thought to be beginning to evolve away from the main sequence, having consumed almost all the hydrogen in its core in nuclear fusion reactions.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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