ISS transiting the Sun

click image to enlarge

Yesterday (June 23, 2014) near 16:15:29 UT (18:15:29 CEST), the International Space Station (ISS) passed in front of the solar disc as seen from my observing location in downtown Leiden. As can be seen in the picture above, the transit was nearly central (the calculated central line was 600 meter to the north of me). The whole event had a duration of about 1.5 seconds, during which 9 photographs captured the Space Station silhoueted against the sun. The images were made with my Canon EOS 60D through my Celestron C6 (15 cm Schmidt-Cassegrain), fitted with a Solar Screen filter and an F/6.3 focal reducer. The sun was low in the sky at an elevation of 31.8 degrees due West. The inset is a stack of the 5 best ISS silhouets.

The images are not perfectly sharp, which is due to air turbulence (even at 1/4000 second) and the simple fact that I find it quite hard to focus the telescope properly on the sun, certainly when it is almost featureless. Nevertheless, I am satisfied with this image.

I knew of the transit because I subscribe to alerts from CalSky for this kind of phenomena. In preparation for the actual observation, I download the latest ISS elements from Space-Track a few hours before the event, and load them into Guide to fine-tune the transit time and the path over the solar (or lunar) disc. Starting about 1 second before the calculated commencement of the transit, I start a rapid burst series of images at 5.7 images/second.

click images to enlarge

Above are two pictures of the setup used. The filter mount is homebrew and quite simple (from thin cartboard). The filter itself is Solar Screen, a mylar filter with a double thin aluminium filter coating. Using such a filter makes it safe to look at the sun (NEVER look at the sun without a proper filter!).

In order to be able to see anything on the camera LCD screen in the bright sunlight, I put a towel over my head and the telescope back during focussing.