This past week was “Manhattanhenge” in New York City. This event occurs twice per year, on both sides of summer solstice, when the setting sun aligns exactly with the street grid.
The name is derived from Stonehenge, which shows a similar phenomenon exactly on solstice. While Stonehenge is believed to have been built specifically with this light effect in mind, Manhattanhenge is just an artefact of the street grid of Manhattan.
Manhattan’s numbered streets run almost exactly East-West, and the Manhattanhenge effect occurs quite close to the solstice: about 3 weeks before and after the Sun reaches its highest point in the sky in summer. This time of year the sunset is quite late, so Manhattanhenge usually occurs between 8:15 and 8:30 PM.
The grid layout for cities, with its long uninterrupted roads, is quite popular in North America, and Manhattan isn’t the only place with a Stonehenge-like phenomenon. Any flat city with grid layout in approximately East-West orientation will do. The further the grid is from this orientation, the further the dates will be from the actual solstices. In Toronto, a similar phenomenon occurs on dates around the winter solstice, in late October and in February. In February, the sun sets right around the time everyone is driving home from work, and as a result, the February date of Torontohenge is a peak date for road accidents in Toronto!
Other accidental urban Stonehenges, with dates much closer to the actual solstices, are for example Washington DC and Baltimore, where the streets run almost exactly along an East-West line. Meanwhile, Manhattanhenge is back on July 12.