May 30, 2012 at 1:18 PM ET
The first night of this year's Manhattanhenge season was a washout, due to cloudy weather, but there's another chance to see the sunset turn the streets of New York aglow tonight.
Manhattanhenge refers to the perfectly placed alignment of the setting sun amid the canyons of midtown Manhattan's east-west streets. The phenomenon, sometimes known as the Manhattan solstice, occurs every year around Memorial Day and major-league baseball's All-Star break.
The Hayden Planetarium's director, Neil DeGrasse Tyson, says future archaeologists might well conclude that these spots on the calendar marked important rites of summer for New Yorkers. (And they wouldn't be far wrong.)
Tyson's the one who came up with the term "Manhattanhenge." Think of it as a modern-day, unintentional version of Stonehenge, with New York skyscrapers standing in for the stones of the 5,000-year-old monument in England.
Stonehenge was constructed to have its stones line up with the rays of the sun on important astronomical dates such as the summer solstice. Manhattan's street grid, however, doesn't line up with the solstice or the equinox. The relevant streets, which reflect the Commissioner's Plan of 1811, are offset 29 degrees from east and west. That would spoil the sunset view on an equinox or a solstice — but on the proper dates, the sun reaches the cleft between skyscrapers just in time to set the streets aglow.
This year's first opportunity for seeing Manhattanhenge's glory came Tuesday night at 8:17 p.m. ET. Under ideal conditions, a pretty half-setting sun could have been seen centered in the gap between the buildings. Unfortunately, conditions were not ideal. In disappointed Twitter tweets, the sight quickly came to be termed "Cloudhenge."
"A cloudy and stormy night, so no sun," reported Andrew Dallos, a producer for "The Rachel Maddow Show" on MSNBC who camped out on 42nd Street.
Tonight, on Wednesday night, New Yorkers could get a chance to see the sun's full disk just touching the horizon in the gap at 8:16 p.m. ET. It all depends on the weather: The current forecast calls for partly cloudy skies with a slight chance of thunderstorms — which at least sounds more promising than last night's weather.
Even if tonight's opportunity is clouded out, there'll be a Manhattanhenge replay after the summer solstice, with a full-sun viewing at 8:24 p.m. on July 11 and a half-sun opportunity at 8:25 p.m. July 12.
To enhance your Manhattanhenge viewing experience, Tyson suggests positioning yourself as far east as possible, while still making sure you can see New Jersey when you look west across the avenues. "Clear cross streets include 14th, 23rd, 34th, 42nd, 57th and several streets adjacent to them," he writes in his viewing guide. "The Empire State Building and the Chrysler Building render 34th Street and 42nd Street especially striking vistas."
Thanks in part to Tyson's efforts, Manhattanhenge is the best-known of the modern-day monumental alignments. The clear prospect to the west between New York's towering buildings makes for a nearly unbeatable scene. But other locales have their own "Henge" dates, due to the unintentional effects of a street-grid layout or an architectural feature. Here's a sampling:
Baltimorehenge: The sun lines up with downtown Baltimore's street grid for sunrise on Sept. 18 and March 25, and for sunset on Sept. 29 and March 12. The Baltimore Sun's Frank Roylance explains it all for you.
Phillyhenge: The sunrise moments have come around March 1 and Oct. 11, and sunset alignments are around April 4 and Sept. 5. Precise dates vary from year to year. The Photographer's Ephemeris helps you find the proper lineup.
Torontohenge: The sun lines up with Toronto's street grid for sunrise on April 17-18 and Aug. 23-24, and for sunset on Feb. 15-16 and Oct. 23-24. This entry from Torontopedia helps you figure it out.
Other urban "Henges": If downtown streets line up more precisely with a true east-west axis — as they do in Chicago, Washington and Portland, Maine, for example — the "Henge" moments come around the March 20-21 spring equinox and the Sept. 21-22 autumn equinox.
MIT-Henge in Cambridge, Mass: The rays of the setting sun light up the "Infinite Corridor" at the Massachusetts Institute of Technology in late January and during the second week of November. This video fills in the details.
Do you know of other monumental alignments? Clue in the rest of us by leaving a comment below.
More celestial alignments:
This is an updated version of an item originally published on May 29.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.