How do you know the time without a clock? Please tell me your way.

Sundial: used during the day. Need to know the local latitude, local time is measured. If the latitude is unknown, it can be obtained by measuring the height of Polaris (or Southern Cross) at night.

Starry sky: used at night. You need to know the date of the solar calendar, and the local time is calculated. . In a year, the sun walks around the starry sky and knows the position and calendar of non-solar stars, so it will know the position of the sun. If you don't know what day the calendar is, make a more accurate sundial and then work it out.

The position of the moon in the starry sky: sextant and calendar are needed to measure Beijing time!

The position of Saturn's satellites: a telescope is needed to measure Beijing time.

Hourglass, incense, water leakage

radio