Posted by: Rob T | March 21, 2010

Looking up (at) the ISS

The International Space Station

I recently posted on Facebook that I had (again) run outside with the kids to watch the ISS fly overhead.  A few of my friends posted some questions that I thought could be answered in a blog post and shared with everyone, because this is something that more people should know about; that more people should do with their kids.

So here is your quick guide to watching the ISS go overhead.

By the way, just so everyone knows what to expect, you’re not going to see the space station’s structure or anything – you’re going to see a bright speck of light.  The ISS flies overhead at an altitude of over 180 miles, so you won’t see anything but that bright speck.

The first thing you need to know is where and when to look.  For that, I wholeheartedly recommend http://www.heavens-above.com.  What this site lacks in looks it makes up for in sheer power.

Heavens-Above Needs To Know Where You Are

When you first enter the site, it won’t know where you are, so you need to tell it, and there are a few different ways – you can zoom into and mark your location on a Google Map, you can use the site’s database to find your location, or if you happen to know your exact longitude and latitude, you can enter it manually.  You can also make an account so that when you come back, you just log in and it remembers who you are.

OK, so now the site knows where you are, and you’re ready to look for satellite passes!  A little lower on the home page is the Satellites section, and the first link is for the next 10 days of passes for the ISS.  Something like this…

Upcoming Satellite Passes

“Woah”, I hear you say.  “That’s a lot of data!  What does it all mean?” Don’t worry.  It’s not as bad as it looks.

On the far left are the date and magnitude of the pass.  Then you’ve got three sections for when the pass starts, peaks, and ends.  So you can see that for the pass on April 7:

  • At 5:15 AM, you would want to be facing west-southwest to see the beginning of the pass.
  • At that time, the satellite will begin to be visible at 20° above the horizon.
  • At its peak (about 2 minutes later), the ISS will be at 58° above the horizon looking northwest.
  • It will set about 3 minutes after peak at 10° above the horizon in the northeast.

Now, what about that “magnitude” value.  -3.2“Is that good?” you ask. Yeah, that’s really good.  Apparent magnitude is an odd sort of astronomical measurement of brightness that makes sense if you know where it came from, but I’ll let you follow that link if you’re curious.  What you need to know is this:

Human eye limit roughly +6.5
Faintest objects visible in urban areas roughly +3.5
Polaris (the North Star) +1.97
Sirius (the brightest star) -1.44
Mars (at brightest) -2.9
Faintest visible daytime objects -4.0
Venus (at brightest) -4.4
Full Moon -12.7
Sun -26.7

So you see that this pass will be brighter than even Mars at its brightest, and will be outshined only by Venus, the Moon, and (if it were up) the Sun.  Given that these passes are only listed for times when the sun is down, and it’s possible that both Venus and the Moon will also be down, the ISS could easily be the brightest object in the sky as it passes.

The other thing to realize with a pass as bright as -3.2, don’t be discouraged if it’s a little hazy outside.  Or if you’re in a big city with lots of light pollution.  Step outside, get used to the dark for a while, and if you can see ANY STARS AT ALL, you’ll be able to see the ISS.

“But Rob,” you say, “can I visualize the track, rather than rely on these compass directions?” Absolutely.  Notice that the date of each pass is blue.  Just click on it.  You’ll get lots more details about that pass, including a convenient sky map:

Map of ISS Flyover

If you’ve never looked at a sky map before, the outer circle represents the horizon, and the center of the map is directly overhead.  You’ll also notice that East and West appear backwards.  That’s because you’re supposed to look up at this map, not down on it like other maps.  To make the compass directions work out, just imagine holding it up over your head.  I have actually done this before – print out a sky map and taken it outside with me to make sure I had the right directions.

Here you see this nice arc drawn across the sky showing the path of the ISS as it flies overhead.  It’ll appear near Virgo, fly through Bootes and Draco, then Cepheus and Cassiopeia before setting in the Northeast.

OK, so now you know WHERE to look, and WHEN to look (oh, and by the way, if you’re a night owl, not an early riser, plenty of passes happen at early evening hours – they’re not all pre-dawn times).  So the question becomes – do I need to bring anything else with me?

Well…  Not really!  This isn’t like watching a meteor shower, where you need to bundle up since you’ll be out there for a while.  You can be in and out in 10 minutes.  And a telescope wouldn’t work – the ISS moves too fast.  It’ll take about 6 minutes to completely fly overhead.  You could try binoculars, if you want, but I really recommend – especially for the first few – to just go outside and watch.  And take people with you.  Especially kids.

Take them out there, show them this point of light in the sky, zipping along, and tell them “We built that.  We put it up there.  And there are astronauts living up there right now, flying around the earth at over 17,000 mph.  And 45 minutes from now, they’ll be flying over the other side of the world.”

If that isn’t cool, I don’t want to know what is.

..Rob T. missed tonight’s Magnitude -2.9 flyover because of accursed rain clouds!

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Responses

  1. Ok… we need an Iphone app for that…

  2. There are a couple, but neither is free, and I don’t believe either stores the data offline for iPod Touch users (or when you’re outside of cell phone range).

    http://www.gosoftworks.com/GoSatWatch/GoSatWatch.html

    http://www.appstorehq.com/issvisibility-iphone-42830/app

    What we really need is a way to subscribe to an iCal feed of the upcoming passes…

  3. I also recommend Twisst. Simply follow @twisst on Twitter and they’ll send you a message each day about when the ISS will be overhead.

  4. Twitter users can follow @twisst for updates based on their twitter location….

  5. NASA has an easy to use website that shows you all visible passes of the Space Station and Shuttle (when flying). Just click on your state/city.

    http://spaceflight.nasa.gov/realdata/sightings/cities/skywatch.cgi?country=United+States

    Outside of the U.S. – choose your country on this page:
    http://spaceflight.nasa.gov/realdata/sightings/


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