Daily Solar Altitude

This shows the sun's altitude over the current day starting at local midnight. The points where the altitude crosses the zero line indicates sun rise and sun set (not adjusted for atmospheric refraction). The distance between them is the length of the day. The solstice lines indicate the maximum and minimum range of the sun position through out the year.

The earth's axial tilt is 23°-ish so a midnight sun happens at an extreme latitude, e.g. near the polar circle, for example on the summer solstice at 66°N Conversly, it is darkness at noon at on the winter solstice at 66°N. The well that "had no shadow at noon on the solstice" Eratosthenes uses to calculate the earth's circumference is 23°N and on the summer solstice.