If you've ever looked up to the night sky to see the International Space Station zooming by (if you haven't, you can find out when to look for it here), you know it goes by at quite a clip -- 7.66 kilometres per second, a dot only a little brighter than the stars. Photographing it, therefore, takes planning, skill and no small amount of luck.
That was the case for a shot like the above, showing the ISS in transit across the face of the full moon taken by Byron Bay, Australia astrophotographer Dylan O'Donnell. It took 12 months of careful waiting and planning to make the most of his fraction-of-a-second window. Although ISS flyovers are frequent, there's a lot of sky for it to pass through, and lining up directly with the moon, let alone the full moon, happens rarely.
"The CalSky website sends me alerts for potential flyovers, for which I've been waiting a long time -- about 12 months. I got one this week and this was adjusted by 15 seconds by the time of the 'occultation'," O'Donnell explained on his blog.
To photograph the event, he used a Canon 70D attached to a Celestron 9.25″ telescope (2300mm / f10), using a shutter speed of 1/1650th of a second and ISO 800.
"If you think that it might be a case of sitting there with your camera and a clock, with one hand on the shutter release, you'd be absolutely correct! The ISS only passed over the moon for 0.33 seconds as it shoots by quite quickly. Knowing the second it would pass I fired a 'burst' mode of exposures then crossed my fingers and hoped it would show up in review -- and it did!"
In order to get such clear detail on the moon, O'Donnell took a further second of exposures on each side of the ISS' lunar transit, then edited the photo, increasing the colour saturation to show the details on the lunar surface clearly.