2018年IAO理论低年组第1题-水银镜面

Mercury mirror. As you know. If one rotates a vessel with mercury, its surface will take a parabolic form. A kiquid mirror obtained in this wan can be used as the main mirror of a telescope. The Polar Bear-astronomer living in the Arctic decided to use this idea and build such a telescope exactly at the Norht Pole, and use the daile revolution of the Earth as the rotation mechanism so that the main mirror would have a long focal length.