Every time it passes overhead and I’m there to watch, several passersby are curious about my pointing finger. “Take a look", I say to them. “See that bright object that’s moving?" Many people stop and stare, often in wonder and delight.

There are others, though, who refuse to look up. Face set in grim masks, without a second look at me, they push past and resume walking. Somehow, they have been persuaded that looking at something in the sky is dangerous, either to their health or their psyche or both. “It’s the International Space Station (ISS)!" I’ll say as they pass. “Not often can we see it like this!" I may as well be speaking to an octopus, for all the effect I have on their rapidly receding selves. I know they have their beliefs, but the irrationality of it all—irrationality, in the face of the ode to human ingenuity that’s zooming past up there—invariably leaves me just that little bit sad.

But not for long. Because the others more than make up. We’ll stand there together, our heads tilted way back, watching what is for a few minutes the brightest object that’s not the Moon race across the night sky. Sure, it’s just a gleaming white dot, but those moments are filled with an almost inexplicable thrill, a strangely exciting feeling of being somehow connected to the intrepid astronauts in that spacecraft, somehow part of this most remarkable of human endeavours.

“Hey, did you see Sunita Williams waving?" I’ll ask, and the “yeah right!" looks I get are like the icing on top.

the ISS passing in front of the Milky Way, in Wales, UK. Photo: Alamy
the ISS passing in front of the Milky Way, in Wales, UK. Photo: Alamy

Every few weeks, Nasa notifies me of an upcoming close encounter with the space station. This factoid never fails to impress my fellow-watchers when I tell them—“You work for Nasa? Wow!"—but it sounds infinitely weightier than it actually is (no, I don’t work for Nasa). Anyone in the world can sign up for these alerts in a matter of seconds, and you can get them by email or SMS. That’s how I know when to go look for it.

The Nasa notification shows up when there’s going to be an ISS flyby (properly called “flyover", which usually makes me smile) within the next 24 hours, but only if it will happen at dusk or dawn. Why only at those times? After all, the ISS is circumnavigating the planet all the time, completing an orbit every 90 minutes or so. I mean, I’m writing these words at 1 in the afternoon and I know from a live map of its path that the station passed nearly overhead less than an hour ago. Why didn’t Nasa alert me to that flyover? Why would I not have seen the ISS even if I had looked up at that precise moment?

Well: during the day—or more correctly, when the space station is flying over the part of the planet that is bathed in sunlight—the sun itself is so bright that it drowns out anything else in the skies that might emit or reflect light. When the ISS is sailing through the dark, the sun is on the other side of the planet and the station is too close to earth’s surface for sunlight to reach it. So it’s only in those few in-between moments that the angle is just right and we can see the ISS, via the sunlight that it reflects down at us as if using a gigantic mirror. If you have signed up to get the ISS alerts, Nasa checks whether the ISS will fly over your location on earth during those charmed dusk or dawn hours. If so, you will get a message like this:

Spot the Station. Time: Wed Apr 19 8:05 PM, Visible: 3 min, Max Height: 41°, Appears: 30° above W, Disappears: 22° above S

Here’s the thing. I get this notice and I go out a few minutes before 8.05, looking west. At exactly 8.05pm—not 8.04, not 8.06—the bright dot appears from exactly that direction. Unlike almost anything in the sky, it’s moving, certainly moving faster than anything in the sky that’s not a plane. It gets a little brighter as it gets higher in the sky. Exactly 3 minutes after it appeared, it’s gone.

US astronaut Scott Kelly inside the ISS cupola. Photo: Reuters/NASA
US astronaut Scott Kelly inside the ISS cupola. Photo: Reuters/NASA

This is what it’s been like, every single time I’ve walked out into the open to see the ISS.

The precision is impressive, remarkable. And yet it should hardly be a surprise. Even if the ISS is orbiting the earth at a rapid clip, we know exactly where it is at any given moment. There are websites which track its movement in real-time. We know that its path shifts with each orbit, and you can see that happening on those tracking sites. You learn that it is travelling at upwards of 27,500 kmph, some 400km above us. You can find out about upcoming sightings in your location. In my case, the next one is on 15 November, with the time and direction and altitude listed exactly as I know it will be in the email that will arrive on 14 November. There’s even a feed from cameras mounted on the station, so you get an idea what our planet looks like from up there (hint: simply gorgeous).

Yes, the precision is impressive. But if you think about it, that’s just the way it has to be. Space exploration would be impossible without such precision. To get a sense of what I mean by that, consider just one example.

The ISS over London. Photo: Alamy
The ISS over London. Photo: Alamy

As you no doubt know, we have sent spacecrafts to Mars; India’s own Mangalyaan has been orbiting that planet for over four years now. How did we manage this feat, given that on average, Mars is about 220 million km from earth? Let’s say we took aim at Mars one balmy evening, imagining a straight line linking the planets, and sent Mangalyaan shooting towards Mars much as you might shoot a gun at a target. What would happen if you were even a tiny fraction off in your aim—a thousandth of a degree, say? With a typical gun and its target, such an error would not matter at all. Your bullet would still hit the bull’s eye. But with a certain red planet that’s 220 million km away, you’d be off by nearly 4,000km. That is, with an error like that, Mangalyaan would fly comfortably past Mars and off into the vast empty spaces beyond. Let’s face it: we cannot afford an error like that.

In reality of course, this is nothing at all like how we send spacecrafts towards Mars, or anywhere. Because both planets are moving, because we have to account for and in fact take advantage of their respective gravitational fields, because we must also take advantage of those times of year when Mars and earth swing closer together than 220 million km, because of a host of other factors—saying the path Mangalyaan took to reach Mars resembles a straight line is like saying my tennis game resembles Roger Federer’s (hint: it doesn’t). After it launched, Mangalyaan made a number of ever-widening elliptical orbits around the earth, the last of which then essentially catapulted it on a long trajectory to where it now is—circling Mars. Straight line? Not on your life.

And yet that complicated path is itself also a reflection of, a tribute to, the same idea of precision in space travel. Think of the calculations needed to account for gravity. Or to get Mangalyaan orbiting the earth, but wider each time. Or to settle it into orbit around Mars. Get any of that even slightly wrong and the craft will crash back to earth, or go careening off into space, or even explode.

In some deep way, all this is why I signed up for those Nasa ISS alerts. This is why I go out to watch the station, most times that I hear it will be visible. This is why it never fails to thrill me when it appears. This is why I urge others around me to look up at that shining dot too, as it speeds past overhead.

Swirls in the sea off Mumbai, captured by retired Canadian astronaut Chris Hadfield. Photo: Twitter/@Cmdr_Hadfield
Swirls in the sea off Mumbai, captured by retired Canadian astronaut Chris Hadfield. Photo: Twitter/@Cmdr_Hadfield

For it’s much more than just a bright moving dot, pretty as that sight is.

The way I see it: Down here on earth, we have our irrationalities and murderous quarrels and filthy rivers and lying leaders and meaningless monuments, and often enough, it all gets me down as I’m sure it gets you down. But then you can look up and marvel at that dot, that symbol of the finest qualities of our species. Everything about the ISS—from the precision of its path to the way it has been built, from all it seeks to achieve to the courage of the people inside it—speaks to me of the wonder of science and the generous spirit of humanity.

As the International Space Station completes 20 years in orbit, that’s something to think about.

Want to sign up for the alerts? Go to http://spotthestation.nasa.gov