Mnajdra south optical calendar is the last in a series of design improvements and alterations. Grand in style and dimensions, it is the apex of more than 3000 years of development in megalithic calendar design and building.
Time around the equinox was still followed by the old system, a central partial apse at the back, a remnant of the horse-shoe apse. For time around the solstices the side ‘solstice marker’ was used. This was a more accurate method, permitting the predicting of the solstice day and time accurately.
The odd appearance belies the evidence of an important alteration that was implemented at some time after it was built. Originally it had a field of view, solstice to solstice, of about 36 degrees, same as several earlier others. The display surface was extended (solstice extenders) at a later date to a field of view of about 58 degrees ( today’s earth tilt ).