Jun 30

ISS – Daytime lunar transit (less favourable)

Lunar transits are becoming one of my favourite events lately,  the thrill is something like with no other celestial events. My heart is pounding harder and harder as the transit time approaches, triple checking every single details just in case if I missed something. And when the right time has arrived I just wait for a flash, a miniscule duration appearance of the International Space Station. Knowing that 3 astronauts are riding on that vehicle at the moment is always something that leaves my speechless.

I saw a not extremely promising ISS lunar transit event on the transit forecast websites.

Transit forecast

But why is this event less favourable?

Mainly it is down to a few factors. For a start Moon is relatively low in the sky (32° above horizon), therefore at the time of transit ISS was at the same elevation. it means ISS was relatively far away (higher in the sky, closer to the observer’s location), precisely 727 km away. Because it is quite far away, the apparent size of ISS is 38 arcseconds (not good but not bad either).

The list of disadvantages is not complete yet. Sun is rising at 4:46am, but the the transit did not happen till 6:30am, which only means Sun was at 13° above horizon. Moon was already pale and was harder and harder to see craters. Therefore the same applies to ISS as well, less details to make up. I knew all these from previous experience, but the weather improved so much in the past few days after weeks of rain and cloud that I had to do this for maintaining the balance of my inner peace haha… And it was a gorgeous morning which I love so much in summertime.


And the final result summarised in one video. The quality was so bad (for my own standards) that I could not make a nice high resolution photo from the frames. So this time around I only have a video.



Skywatcher 250/1200 Flextube dobson telescope
Zwo ASI224MC camera


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