Catching the International Space Station — Loran Hughes Astrophotography

Obligatory Warning: Never point your telescope at or view the sun without a proper solar filter!

The International Space Station orbits the earth 15 1/2 times per day at an altitude of 250 miles, traveling at 17,100 mph. Once in a while, the ISS will be visible with the sun or moon in the background from your location. It completes these transits in under a second, as can be seen in this video I did back in 2018.

I use the ISS Transit Finder site to keep tabs on upcoming nearby events. I hit the proverbial jackpot on June 17, 2020 with both a lunar and solar transit visible from my driveway. I arranged to take the day off and started checking the long range weather forecasts. The cloud cover was looking good for both passes.

Two transits on the same day? Time to buy a lotto ticket!

My plan was simple. Set up the night before, get polar aligned and get some astrophotography in before the next day’s events. The telescope would be in focus and ready for the big dance.

I decided to use the William Optics GT-81 refractor with a ZWO ASI178MC-Pro camera, which would give me full frame images of the sun and moon.

Then the weather forecast changed the day before the scheduled transits. It would be cloudy until early the next morning. I rolled with it and decided to set up at about 3:30 am, when I could still get a polar alignment. Unfortunately, we were still socked in with clouds that morning. The time for the lunar transit came and went. Then the cloud cover broke a half hour after the lunar transit. Weather 1, me 0.

Solar filter attached and ready to capture the ISS transit.

I roughly aligned the telescope mount to the north and hoped it would be good enough. Next, I found the moon and set it in the mount’s pointing model. Focus was done by eye, using the few craters I could see in the sliver of the waning moon.

The moon wasn’t giving me much to work with.

I was as ready as I could be. I attached the solar filter to the telescope, lined up on the sun and waited for the appointed time.

Capturing the Image

How do you capture something that will be visible for under a second? Video. Using SharpCap Pro, I set the image size somewhat smaller than the camera’s full resolution, set the output to SER video and was able to coax 11 frames per second out of the camera. I figured that would give me seven images maximum. I ended up with six.

About a minute before the transit, I hit the record button and waited. It wasn’t long before I saw the ISS zip across the screen. At that point, I stopped recording and packed it in.

Processing the Final Image

I used PIPP to extract TIF images from the video, then it was a matter of viewing each one to find the ISS. Once I found my six images, I sharpened each one slightly with Topaz Sharpen AI, then created a composite image in Adobe Photoshop.