Wednesday 18 February 2009

The International Space Station with the naked eye

Some years ago, translating into Spanish the book Out of the Blue, by John Naylor, I learned it was possible seeing artificial satellites (see section 13.3 of the book). Well, actually I didn't learn it, I just believed in what the author said. It's funny, but the author was encouraging us all the time to be less bookish and try to learn things through our own experience, but I didn't try this.

I remembered this last month. I found in (here to be precise) two guys who said they had seen the International Space Station (presumably with the naked eye). In fact, the ISS is big enough to be easily observable with the naked eye, and apparently it can be seen with no problems from most of the places of the world (excluding paces above 63º N or below 63º S).

So I had probably the most essential ingredient an experiment needs: an idea to test. This idea was:

I can see the International Space Station with the naked eye.

For this experiment I used two tools:

  • the website (a website with loads of information about when and where you can see the ISS, including the path of it across the sky or the apparent magnitude of it).

  • the alarm of my mobile phone.

I had some chances to see the ISS after sunset in late January, but some days I left work late, or I forgot about it, and other days it was cloudy or rainy. So I missed this period.

Recently it started being observable again before dawn (according to the mentioned website). I saw that 18th February was promising, as the ISS was going to have an apparent magnitude of -2.3, making it brighter than any other star in the sky (and even brighter than Saturn and Mercury, which were in the sky at that time). According to, from El Goloso (I put El Goloso as my place, which is near, as Tres Cantos was not in their database of places) it could be seen from 7:08:37 (time at which the ISS was going to leave Earth's shadow) to 7:16:20 (time at which it would disappear behind the horizon).

I set the mobile alarm for 6:58, and when I got up, I saw the sky was clear, as I could see stars very well. I checked which window was providing a better sight. Apparently it was going to pass near Vega, and then through Cygnus, which were easily identifiable from my bedroom window even with the city light pollution. So I calculated I would see it from my window at 7:12.

Funnily enough, exactly at that time, a little bit under Cygnus, I saw a bright double light crossing the sky. But... wait! It had a double trail! I didn't think the ISS would leave any trails at all, as it is outside the atmosphere and it is not burning so much fuel. I was puzzled for a few seconds. After that I checked the sky near Vega, and I saw the real ISS (so the other object was with no doubt an aircraft).

It crossed the sky following exactly the path the website told me. I used also binoculars, and this is a drawing of what I saw more or less:

It moved at a constant pace, through Cygnus. After that, it continued to the horizon, quickly losing brightness and becoming smaller and smaller. At 7:16 it hid behind some buildings.

It has been a great experience!