New York City is roughly 41° north of the equator, along the curved surface
of the ball-shaped Earth. In order for the sun to be at the Zenith ... to be
90° above the horizon and shine straight down on New York ... the equator
would have to be tilted 41° away from the plane in which the Earth's orbit
lies. But it isn't. It's only tilted about 23.5° away from that plane. So the
sun can never be directly overhead at any place that's more than 23.5°
away from the equator.