航海英語天文航海單項(xiàng)選擇題每日一練(2019.01.11)

來源：考試資料網(wǎng)

1 A double star is a star that（）.

2 A star that suddenly becomes several magnitudes brighter and then gradually fades is a（）.

3 A marine sextant has the index arm set at zero and the reflected image of the horizon forms a continuous line with the actual image. When the sextant is rotated about the line of sight the images separate. The sextant has（）.

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4 Sidereal time is NOT used（）.

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5 Sidereal time is used by navigators when（）.

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