Practice "ambush astronomy" with the International Space Station

I like to practice ambush astronomy—though a friend of mine would prefer I use a less violent term (“ambassador astronomy”?).

Whatever you call it, it means heading outdoors to a place frequented by pedestrians, accosting (in a non-threatening way) some friendly-looking ones, and pointing out things in the night sky. I've done ambush astronomy with the full Moon ("Hey, did you notice the Moon rising by that building?"), planets ("Look how bright Venus is!"), and most successfully, with the International Space Station (ISS).

One Friday evening the ISS was going to make a visible pass just before I needed to be at the planetarium to give a show. I walked down the block toward the heart of downtown Chapel Hill and waited on the sidewalk. As soon as I spotted the space station—it looks like a very bright star that is slowly but noticeably moving—I turned to a group walking by and pointed it out.

One of them then flagged down the next folks to walk by and educated them about the ISS passing over. Our now large group of people pointing at the sky was irresistible to still more passers-by, who had to pause to see what the fuss was about. Much fun!

Why not practice some ambush astronomy of your own this week with the ISS? Through Friday, its orbit will make it visible from the Triangle area at least once every morning and evening.

If skies are clear, the brightest, most impressive pass will be this Tuesday evening, July 7. At 9:31 p.m., you can see the ISS appear low in the southwest. Over the next six minutes, watch it cross the sky. It will reach its highest point in the southeast, appearing more than halfway up the sky (those watching from the North Carolina coast will see it almost directly overhead). At 9:37, it will disappear low in the east-northeast.

Here are some tips for ambush astronomy with the ISS:

1) It’s okay if you live in a city.

Don't bother if it’s overcast, but do bother even if you live under light-polluted skies. The ISS is now so bright from its various additions that some people have seen it even in the daytime.

2) Start by looking up the next predicted pass for where you live.

NASA has a user-friendly Web site that will prompt you to choose your country, state, and town. I prefer Heavens-Above, which provides more detail on each pass. For this site, you must also begin by specifying your observing site (under the Configuration heading).

3) Before unleashing your space station identification talents on strangers, you might begin with family or friends.

A few minutes in advance, take them outside and figure out where you’ll need to look. To help determine directions you can use your knowledge of where you've noticed the Sun setting this time of year (a bit north of west) or rising (a bit north of east).

4) Tell your group what they'll see.

You might explain how fast the space station moves (more than 17,000 miles per hour), how high it is (more than 200 miles up), how big it is (like a flying football field), why we sometimes see it (its surface can reflect sunlight to our eyes), and how six people living in it may be looking down at you.

You can also join others in trying to spot the ISS at Morehead Planetarium and Science Center’s next skywatching session on Saturday, July 25 (weather permitting). Our session at Jordan Lake’s Ebenezer Church Recreation Area officially begins at 9 p.m., but arrive a few minutes early to see the first of two ISS passes visible that evening.

According to current predictions, the ISS will pass over July 25 between 8:58 and 9:03 pm, starting low in the north-northwest, passing underneath the North star and reaching a maximum altitude of 23 degrees above the northeast horizon before it disappears in the east. (The horizon is 0 degrees, and the top of the sky is 90. The width of your fist when held at arm’s length covers about 10 degrees.)