單項(xiàng)選擇題In general，the most effective period for observing stars and planets occurs during the darker limit of（）.

A.sunset
B.civil twilight
C.nautical twilight
D.astronomical twilight


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1.單項(xiàng)選擇題Elongation becomes zero at（）.

A.opposition
B.west quadrature
C.apogee
D.inferior conjunction

2.單項(xiàng)選擇題During one synodic rotation，a body makes one complete turn relative to the（）.

A.Earth
B.Sun
C.stars
D.vernal equinox

3.單項(xiàng)選擇題Diurnal aberration is due to（）.

A.motion of the Earth in its orbit
B.rotation of the Earth on its axis
C.the body's orbital motion during the time required for its light to reach the Earth
D.a false horizon

4.單項(xiàng)選擇題Capella is found in what constellation? （）

A.Gemini
B.Auriga
C.Libra
D.Crab

5.單項(xiàng)選擇題Because the actual center of some planets may differ from the observed center，the navigator applies a correction known as the（）.

A.phase correction
B.refraction correction
C.semidiameter correction
D.augmentation correction