单项选择题
A.water depth exceeding 100 feet B.fetch C.wind's velocity D.duration of the wind
Mars will not be visible（）.A.at elongation angles near ...
单项选择题Mars will not be visible（）.
A.at elongation angles near 180° B.from quadrature to opposition C.at conjunction D.at opposition
It is difficult to determine which limb of the Moon is ...
单项选择题It is difficult to determine which limb of the Moon is fully illuminated（）.
A.when the Moon is low in the sky at rising or setting B.at the new Moon phase C.when taking Moon sights during daylight D.when the terminator is nearly vertical
In working out a local apparent noon sight for your lat...
单项选择题In working out a local apparent noon sight for your latitude，you subtract the Ho from 90°. The 90°represents the angular distance from（）.
A.the equator to the elevated pole B.your horizon to your zenith C.your zenith to the elevated pole D.the geographical position of the Sun to the elevated pole
