Why is the sundial pointer aimed at Polaris?

Because the earth axis points to the north pole. Every night, the deep night sky is full of stars. In the distant northern sky, a star seems to rise or fall. It is located directly above the North Pole of the earth, and everyone calls it Polaris. Since ancient times, people have the habit of looking at the stars to see the time and Beidou to see the direction. As the saying goes, "Find the North Star, and the direction will be clear" and so on. Let's do an experiment about "the north pole of the earth axis points to Polaris" to find out the secret of the height of Polaris in the northern sky. According to the experimental principle, locate Polaris accurately, aim at Polaris with a stargazing bracket, and draw this straight line according to the principle of three points on a line. The northern end of this straight line is the position of the North Pole Star. Then use the compass to find out the geomagnetic north pole of the earth and draw the geomagnetic north pole line, which are roughly coincident. This means that Polaris is located near the north pole of the earth, which means that the north pole of the earth points to Polaris. Experimental materials: stargazing frame, compass, meter ruler, square table, big white paper, etc. Experimental method: 1. Site selection and preparation: Choose a sunny, starry night with relatively open ground (preferably the roof). Put a 60 cm square table with a big white paper on it. 2. Geomagnetic North Pole Survey: Put the compass needle in the middle of a square table covered with white paper, turn the compass needle, when it stops naturally, record the vertical points A and B of the compass needle at the north and south poles, and then connect them to form a straight line (L_), which is the geomagnetic north pole line of the earth. 3, looking for Polaris: Polaris belongs to the second-class star, not as bright as the first-class star, it is not easy to find in the sky. To find Polaris, we can rely on two famous constellations: Ursa Major and Cassiopeia. These two constellations are easy to distinguish. Ursa major has seven bright stars: Shu Tian, Tian Xuan, Tianji, Tian Quan, Yuheng, Kaiyang and Yaoguang. They form a spoon, commonly known as the Big Dipper. The five main bright stars in Cassiopeia form the letter M. The positions of these two constellations in the sky are just opposite the Polaris. Find the approximate location. Then find the outermost two stars of the Big Dipper-Shu Tian and Tian Xuan, connect them with imaginary lines, and extend five times from Tian Xuan in the direction of Shu Tian, and you will meet a bright star, which is the North Star. 4. Measuring the North Pole Line: put the stargazing bracket on the square table, adjust the stargazing bracket up, down, left and right, so that the two observation well P and Q of the stargazing bracket are in a straight line with the three points of Polaris, and at the same time, make the vertical foot of observation well P coincide with the point A on the geomagnetic north pole line L_. Write down the foot C of observation well Q, and then connect A and C to form a straight line L_, which is the North Pole of the Earth. 5. magnetic declination: the direction pointed by the compass mentioned earlier is not due north. The north of the compass is not strictly aligned with the direction of Polaris, but has an angle. This shows that the earth's north and south poles and the geomagnetic north and south poles are not in the same position, but have an angle, which is called declination. The magnetic declination varies from place to place. In the east of China, the direction of the magnetic needle always points to the west of the North Pole, which is called west deviation. The farther northeast, the greater the angle of west deviation, such as Shanghai 3-4, Luda 5-6, Heilongjiang 1 1. In the western part of China, the direction of the magnetic needle always points to the east of the North Pole, which is called east deviation. The farther to the northwest, the greater the east deviation angle, such as 0 in Lhasa and Qamdo, and 3-4 in Urumqi. The experimental conclusion is that the angle between geomagnetic North Pole L_ and North Pole L_ is about 1-2 _ (in Jingzhou, Hubei). Therefore, the position and direction of the North Star is the North Pole of the Earth. As long as we find the North Star correctly, we can tell the direction. Source: Children's Science Weekly Teaching Edition