Faherty lectured a group of several hundred people at the Hayden Planetarium at AMNH last night to explain the science and history of Manhattanhenge. The event occurs because of how the orientation of Manhattan's grid aligns with the location of the Sun. The Earth spins on a tilt, so as it orbits the Sun and the year progresses, different parts are exposed to different amounts of sunlight. North of the equator, the longest days are in the summer, when the Sun is high in the sky and rises and sets north of east and west. As winter approaches, the Sun appears to move south and lower in the sky, until the winter solstice when its arc is shortest. Afterwards, the days grow longer as the Sun moves north, and the cycle continues.