Kevin -
I assume that you mean "at the zenith." The question is sort of confusing, and the answer is non-specific. Since the Earth sits at a 23.5 degree angle relative to its orbital plane (the ecliptic), there are several locations on the surface where the Sun can be seen directly overhead at different times of the year. Since the Earth is turning and orbiting, the Sun is never in the same place at the same time every day. But it can be at the zenith for a brief period for any location on the Earth that is aimed directly at the Sun. This always occurs at exactly noon local time, but of course it never occurs at the poles, since they never point directly at the Sun. The locations that do point directly at the Sun all lie in a region that is bounded by two lines circling the Earth at plus and minus 23.5 degrees latitude. Along those two lines (the tropics) the Sun can always be seen directly overhead for one day a year at noon. Between those lines, it can be seen directly overhead for two days a year. At the equator, for example, the Sun is seen directly overhead at both the vernal (spring) and autumnal (fall) equinox. At the northern tropic, this only occurs at the summer solstice for the northern hemisphere.
