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

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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

单项选择题

A star is observed at lower transit. The line of position derived from this sight is（）.

A.on the prime vertical
B.a latitude line
C.a longitude line
D.of no special significance

单项选择题

A sidereal day is shorter than a solar day. This difference is due to（）.

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