Astrometric Limit: The maximum residual in the place of a reference star, specified in arc seconds.

天文测量误差极限：参考星位置对应的最大误差，用角秒表示。

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Visible light telescopes can resolve a piece of sky just a few arc seconds across — at least 60 times a smaller patch of sky than can be resolved with the human eye.

光学望远镜在数角秒内就能获取一张星空图—至少比肉眼能获取的大60倍。

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It is the ability to separate two closely-spaced stars into two distinct images measured in seconds of arc.

也就是能够分开两个距离很近的两颗星的能力，单位是角秒1(seconds of arc)。

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Degrees are divided into minutes (sixtieths of a degree) and seconds (sixtieths of a minute) of arc, so that there are 3, 600 seconds of arc, or arcseconds, in one degree.

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He missed the front end of a pair of one-and-one chances and was off on a jumper from just inside the arc with 29.2 seconds left and the score tied.

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