If you're lucky enough to live in a city with a downtown grid, twice a year the sunset will split the middle of the east-west streets, bathing the urban core in a warm glow of orange light. And here in the capital, we think December 5th might be the day that—if the weather cooperates—best represents the spirit of what we're calling "Ottawahenge."

	The alignment of the sunset along Laurier Avenue on Dec. 5, 2011. Image via The Photographer's Ephemeris

We used The Photographer's Ephemeris (big ups to OpenFile freelance photographer Justin Van Leeuwen for the tip) to figure out on which date the sun would be best aligned with Sparks Street. Why Sparks? Because as this Flickr photo from 2009 shows, the architecture lining the pedestrian walkway makes for some stunning atmosphere. Also, you can plant your tripod in the middle of the road without being flattened by rush-hour traffic, which is nice.

Based on our calculations, it looks like Dec. 5 is an ideal day to shoot some sunset photos on Sparks Street. That said, a few days on either side shouldn't make a big difference. And in all honesty, from our Queen Street office, we've noticed some amazing late-afternoon light spilling through the skyscrapers for a few weeks now.

But why "Ottawahenge?" Well, it has to do with a similar biannual event in Manhattan that's become part of the cultural zeitgeist. Each year, Manhattanhenge occurs around May 28, and again near July 12. (The above photo was shot two years ago on July 12, by the way.) There are similar days in Toronto and Montreal—in 2009, Walrus Magazine held a photo contest asking for the best shots of that year's Torontohenge—and the reference to Stonehenge is inspired by the way the sun aligns with the rocks on the solstices.

So get out there and fire off a few photos, OpenFile readers. And if you send them to us, you could be the winner of the First Annual OpenFile Ottawahenge Photography Contest! To enter, email one photo—and only one—to trevor [at] openfile [dot] ca by midnight, Dec. 5. Use the subject line "Ottawahenge."

Since the weather can be up and down these days, we'll accept any photo shot between now and Dec. 5. The winner gets $75 (woo!), and we'll also make their shot our featured blog post.

Photo by Dan Nguyen @ New York City on Flickr