When I was very young I remember the grown-ups around me would often talk about the scale of vast things -seven-figure numbers, the solar system, the galaxy and so on- as “unimaginable”. Even the earth seemed vast. I’ve often reflected on this since, usually thinking to myself that as I’ve got older such things have become more and more “imaginable”.
This reoccuring line of thought popped up again recently. The International Space Station has been making regular passes over Britain during June. One evening, I’d been watching the ISS Live Stream online. The stream was showing the earth as seen live from the ISS: below the station, the world was in daylight. Ahead, the “sunset line” was looming up, beyond which the world faded into darkness. I left the computer and stepped outside. I was seeing the same view, only from below. The sun had recently set and sunlight glowed from behind the hills. The ISS appeared over the horizon travelling from the light into the darkness, just as it appeared on the laptop screen. Obvious, really – but to see both views at the same time, one from space and one from earth, was uncanny. Another night I tried to photograph it. It was a last minute job. The expected pass was quite late and, I must say, it had been a long day. I was tired. I felt like going to bed. Five minutes or so before it was due to appear over the horizon I finally stirred myself to dig out the tripod, camera and cable release and lug it all into the garden. Five minutes. Everything would have to work first time.
It did. Fumbling in the dark with the controls on the camera, I set it -quite randomly but luckily- to make a 30 second exposure.
So, that’s how far the ISS is seen to travel across the sky in 30 seconds. Looking at the photo, that old train of thought kicked in. It takes about 90 minutes for the ISS to orbit the earth. It took 4 minutes in all to cross the sky visible from our house. By my calculations, that means that 23 people evenly distributed around the earth would have been able to observe its entire journey. OK, so half would be in daylight, but you know what I mean – it made the world seem very small. The line in the photo represents 30 seconds of that journey. It’s just a matter of another simple calculation to work out that 180 such lines joined end to end would represent one entire orbit. That didn’t seem a lot to me.