Up north, down south, left west, right northeast in the sky. This joke tells me what the topic is. Thank you.

China is located in the northern hemisphere, and the direct point of the sun is at most 23.5 degrees north latitude, which is the Tropic of Cancer. The tropic of cancer directly points to the date of summer solstice. For example, if you shine a flashlight on a watermelon (up north, down south, left west, right east), the light in the northern hemisphere will be the strongest if you shine it on the upper third (Tropic of Cancer), and then it will become extremely bright when it is above (North Pole), and it will become extremely dark when it is (South Pole), and the earth will turn from west to east, no matter how it turns to the North Pole, it can be obtained. Light hours will increase in other parts of the northern hemisphere. Check the original post. & gt