More about this
Since the obselisks could be only effective during the day, something else must be created to keep track of time at night. The Egyptians subsequently created the merkhet, which tracked the alignment and visibility of several stars. Known as the “star clock”, the merkhet was designed with a long bar and a plumb line. It also had a sighting tool, with which a user could focus on a particular star and use celestial transit to mark the time.