How to judge solar terms and dates, how to judge the coordinates of direct sunlight points, and how to judge the change of the length of day and night in a certain place.

Latitude measurement: firstly, according to today's date, determine the date of direct latitude of the sun; Secondly, measure the local solar altitude angle B, and if it is temporary at noon, the local latitude is 90°+AB；; Secondly, longitude measurement: on the premise that you want to know the current time of X longitude is t 1, then use t to calculate according to the current position of local time t2 (t2 uses the sun to calculate the height of the current time).