On the solar zenith, the sun is directly overhead at the local solar noon. This phenomenon only happens in the tropics, and other than in the tropics of Cancer and Capricorn will happen on 2 occasions each year. Where I live in San Pablo la Laguna the exact point of zenith is April 29th and August 12th. These two days are 105 days apart, meaning that from August 12th to April 29th is 260 days, tying in nicely with the sacred calendar.
I was a day late for this, I filmed it on August 13th, but the solar zenith angle was 89.7 degrees rather than 90 degrees and my equipment was not precise enough to show that 0.3 degree error. However, you get to see the idea using this setup.