单项选择题
A.irregularities in the daily rotational rate of the Sun B.the space motion of the solar system C.the precession of the equinoxes D.the use of different reference points
A sidereal day is approximately how much shorter than a...
单项选择题A sidereal day is approximately how much shorter than a solar day?（）
A.4 minutes B.8 minutes C.12 minutes D.16 minutes
A sextant having an index error that is off the arc has...
单项选择题A sextant having an index error that is off the arc has a（）.
A.positive correction B.dip error C.negative correction D.semidiameter error
A semidiameter correction is applied to observations of...
单项选择题A semidiameter correction is applied to observations of（）.
A.Mars B.the Moon C.Jupiter D.All of the above
