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
点击查看答案&解析
相关考题
-
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 -
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
