Last week (June 5, 2012), the lucky citizens of Earth were in just the right place to watch Venus's transit across the face of the sun. While this occurred just eight years ago as well, it won't happen again for more than a century. The next time any Earthling will be able to watch Venus dance across the sun will be in 2117 - 105 years from now.

I don't have a scientific background in astronomy, but like any science-obsessed kid, I taught myself how to find the planets in the night sky, as well as how to recognize a handful of stars and constellations (at least the ones that are bright enough to be visible through the smog and light pollution of Los Angeles). These days, when out wandering the streets of Los Angeles doing night photography, I like to look up and see what I can identify, using the Google Sky Map app to confirm my identifications.

Something else I learned how to do as a kid was to view the sun using telescopic projection. Typically, light enters the large lenses of the binoculars (or a telescope), passes through the front lenses, and then strikes the retina of your eye - where the patterns are interpreted by neurons and sent to your visual cortex. In telescopic projection, rather than placing your eye behind the lens of a pair of binoculars, you project the image onto a piece of paper (or a wall, or the sidewalk). Then, all you have to do is adjust the focus ring on the binoculars until the image becomes crisp.

In Los Angeles, the transit began around 3:30pm, and would last several hours, until the sun disappeared beneath the horizon. With that in mind, I grabbed my tripod, a decent pair of binoculars, some painters tape, and a few pieces of white cardstock. In less than fifteen minutes I had constructed a rig that would let me sit back and enjoy the solar spectacle that was about to unfold. All I had to do, as the sun moved across the sky, was to readjust the angle of the binoculars, to keep the projection centered on the cardstock.

I share science with thousands of people every day on Twitter, on Facebook, and on Google+. My blog posts, over the past few years, have drawn more than one million pageviews. In each of those cases, however, people have had to proactively engage with the science I was sharing. They had to "like" something, or "follow" someone, or click a link, or spend a few minutes reading a post. Journalists refer to these people as the "pull" audience. These are people who are already looking for science. Even if I've been able to attract a "push" audience from time to time, such as through random Google searches, readers are still making a proactive choice to engage with the material. While sitting on the balcony, watching that tiny black speck wander across the white disk of our sun, I realized that I was missing a big opportunity to do a kind of scientific outreach that I rarely do.

I collected my rig, walked downstairs, found a sunny piece of sidewalk. By then, it was nearly 4:30pm: prime dog-walking and strolling-to-yoga time. It must have been an odd sight. There I was, fiddling with a pair of binoculars, strapped onto a tripod, pointed at a piece of cardboard on the ground. I certainly received my fair share of awkward sideways glances. One woman was visibly annoyed that she and her dog has to take a slight detour to pass me.

But over the course of around two hours - by which point the sun had disappeared behind the trees - I got to explain a little science to almost thirty people as they walked past. Several were just curious, and seemed to not be aware of the cosmic dance going on thousands of miles above them, as they went about their day. They asked questions like "what are you doing there?" or "what's that for?" A few smiled or nodded as they walked by - and then they stopped, turned, and came back to see what I was doing. (I suspect that those who walked by, and then came back needed a few seconds to put together the fact that Venus was in the news with the strange man on the sidewalk with the binoculars.) I explained that Venus was crossing in front of the sun, and showed what path it would take as it crossed the sun. I pointed out three or four sunspots that were just barely visible.

And it wasn't just astronomy that I got to explain! One observant woman who stopped by with her dog asked why there was red light around one half of the sun's projection, and blue around the second half. I enthusiastically explained a bit of optics, showing that different colors of light refract differently through glass.

Many people - more than I really expected - seemed to already be aware that something was going on with Venus, even if they didn't have the specifics. I chatted about astronomy with an elderly couple taking an afternoon walk, with young women carrying yoga mats, and with young men carrying gym bags. Several asked if they could take photos of it with their phones. After explaining it to one woman, she then explained to her mother, in French, what they were seeing. I talked for a few minutes with one man who interrupted me to say that he was going to run to his apartment a few buildings away to bring his young son back. "He's just getting into science," he said, proudly.

Then, a UPS truck drove by. I watched the driver park his truck, get out, and walk over to see what was going on. In what was perhaps the highlight of my afternoon, I spent twenty minutes talking about astronomy and science with the delivery man. As the afternoon wore on, I had to readjust the binoculars so that the sun would remain visible on the cardstock more and more often.

"So wait," the UPS delivery man said, "we're watching Venus move across the sun, and you have to move the binoculars because the Earth is rotating?"

"That's right," I answered.

"So what we're really seeing is the interaction of three parts of the solar system? Venus, and the sun, and the Earth?"

"Exactly!" I said, excited by the level of sophistication of our discussion.

"And it won't happen again for more than a hundred years?" he asked.

"Nope. Not until the year 2117."

"I'll be dead by then," he said.

"So will I."

There's lots of discussion in the online science community about scientific outreach. Christie Wilcox says that "every lab should tweet." Scicurious thinks that may be asking a little too much, responding that "something's got to give." Miriam Goldstein has excellent tips for using the internet to communicate science. "Science," says Katie Pratt, "has a PR problem." David Wescott may have a solution. They're all right, of course.

In our internet-dominated world, though, it's easy to forget how easy it is to just walk outside and engage with people. To hang out on the sidewalk for a few hours with a pair of binoculars doesn't take funding, or a PR strategy, or any sort of preparation. It doesn't need to take hours away from lab work. You can watch the transit of Venus on your balcony, or you can enrich your own experience - while spreading the science - by doing it on the street. A couple dozen conversations in an afternoon isn't necessarily equal to a million pageviews, but it doesn't have to be. Because the people I talked with were not reading Scientific American, or following scientists and science writers on twitter. They are part of the elusive "push" audience.

It doesn't take much work to make people in that audience open their eyes with wonder or say "wow!" and mean it. Science already does most of that work for us. Just find a reason to hang out on your nearest sidewalk for an afternoon.

Header photo copyright Enrique Gutierrez. All other photos copyright the author.