单项选择题
A.is most accurate before sunrise B.is most accurate after sunset C.should only be observed when the Sun's lower limb is above the horizon D.is most accurate when the Sun's center is observed on the visible horizon
Altair is found in what constellation?（）A.HerculesB.Cyg...
单项选择题Altair is found in what constellation?（）
A.Hercules B.Cygnus C.Aquila D.Capricorn
After Venus passes the point of greatest elongation eas...
单项选择题After Venus passes the point of greatest elongation east in its orbit，the first position in which the elongation will be zero is（）.
A.superior conjunction B.inferior conjunction C.opposition D.None of the above; the elongation will never be zero
A variable star is one that（）.A.exhibits a change in ma...
单项选择题A variable star is one that（）.
A.exhibits a change in magnitude B.has a changing declination C.is increasing in SHA D.is also known as a red giant
