单项选择题
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
A star that suddenly becomes several magnitudes brighte...
单项选择题A star that suddenly becomes several magnitudes brighter and then gradually fades is a（）.
A.double star B.variable star C.nova D.nebula
