Recently the mapmakers at CartoDB declared that Manhattan is not unique in its ability to dazzle us with a sun aligned perfectly with our street grid—they say that most cities can have what we call Manhattanhenge. Even Brooklyn. Also: there are mini-henges that happen all the time, so even our own Manhattanhenge—which we thought only occurred four times a year (two full sun, two half sun)—isn't all that unique. You can now discover 'henges all the time with their handy tool NYCHenge—which they hope to expand to other cities soon.
We reached out to Manhattanhenge founder Neil DeGrasse Tyson for comment, but he was too busy being a famous astrophysicist, so Jacqueline K. Faherty—Research Scientist at the American Museum of Natural History—fielded our questions. What gives with these mini-henges, and why are other cities allowed to have 'henges aren't we special? Here's what she told us:
On other 'henges: "The folks are correct that the experience of having the sun set down East West streets can happen in different areas of the city where the grid is not exactly the same as Manhattan. Indeed, any city with a grid, or even any east west road (such as I-80 which goes across the country) may have a sunglare moment at sunrise/sunset. If you set two rocks together with a width that is close to that of the Sun's apparent diameter on the sky (roughly half a degree) and place them in the East/West direction you have a shot that the Sun will set between the stones at some point in the year. I know there are a few cities that have famous monument 'henge days where the sun sets through a famous arch or structure. The dates where this occurs are a function of the orientation of the grid relative to true East/West as well as the longitude/latitude of the city in question. Be warned that if the grid is aligned too far north/south of East/West the Sun will miss your grid.
I am all for getting other cities on board with their "Henges". We already know of a few that get some attention: Chicago-September 25; Toronto-October 25; Montreal-July 12. Even MIT students have been playing this game in their buildings (see MITHenge which pre-dates any other major watching that I can think of."
On the accuracy of NYCHenge: "The folks at NYCHenge seem to have powered the interactive with the correct Astronomy equations that show the line of the position of the Sun throughout the year. Regardless, for a visual, I prefer to use the interactive that was set up by the National Oceanic & Atmospheric Administration (NOAA) as I know that they use the proper equations to calculate the position of the sun. Also they have a much prettier graphic which labels street names and what not. I can't tell why the NYCHenge team decided to use the visual that they did. I wasn't sure what neighborhood I was looking at and I can't figure out why the streets light up as red sometimes (maybe they are trying to show some sort of illumination?)."
On if we are still special: "I would also note that part of why Manhattanhenge is so special is that (1) we have a clear view to the horizon through the buildings. Looking west, New Jersey does not have many tall buildings and the Hudson River gives us some nice distance between us and the line of sunset; and (2) Manhattanhenge happens in the summer when the sun sets late so people are outside enjoying themselves. We of course have Manhattanhenge sunrise but that happens in the depth of the winter when it is cold, the weather is usually pretty lousy, and you have to get up relatively early to see it."