Cassiopeia Observatory

ISS Moon Transit!
Posted: 8 November 2011

On Sunday, 6 November, I kept hoping the clouds would go away so that I could observe and photograph the sun. Sunspot 1339 is making a nice crossing and is the largest sunspot in years. Unfortunately, the weather did not coorperate. I did manage to get this (cropped) photograph through some clouds with the D7000 DSLR, 300mm lens, f/5.6, 1/250sec, ISO 500, with a solar filter attached.

It was cloudy Sunday night. Monday morning, 7 November, brought some rain, which turned to a brief snow fall:

My Live Webcam captured the weather events during the day. I also posted a very short snow falling video captured with my iPhone 4.

Thanks to an alert from CalSky, I was notified of an moon transit of the International Space Station (ISS) shortly after moonrise on Monday, 7 November, at my location. I began preparing for the event several days ago. The moon would be above the hill at the time of the transit and I had done some test video recordings at prime focus of the 8" LX200-ACF with the D7000 DSLR. All was in readiness. All except the weather. After the morning rain and snow, the forecasts all showed clearing skies by mid-afternoon. However, the forecasts were wrong. The clouds remained. There were some holes in the cloud cover so I opened the observatory at 1621 MST, 53°F. Before I could open the dome, I had to wipe off the water from the rain/snow that had collected on the dome. That done, the dome was opened. At 1625 MST, the moon had risen above the hill and was visible through a small hole in the clouds. I began setting up for my transit imaging attempt. At 1634 MST, quickly viewed the moon at 77X; there was not much contrast against the bright sky background. I then attached the camera at prime focus. I did some focus and exposure test images. Here's what the moon looked like just prior to the ISS transit event through some thin clouds:

Then the race began: ISS vs clouds. Which would cross the moon first? As I tweeted at the time, a big cloud was approaching the moon just prior to the transit time. I started the HD video recording, 1/3200sec, ISO 5000, about 2 minutes prior to the transit and ended it about 1 minute after the transit. The actual transit duration was predicted to be 1.65 seconds at 17h03m57.29s MST. The video ended up being 3m02s. Due to the small size of the ISS against the moon, I was not able to see it cross on the camera's viewfinder. It would take a frame-by-frame check of the video to see if I actually captured the ISS crossing the moon.

Another ISS pass (not moon crossing) was to occur beginning at 1833 MST, so I was very interested in keeping an eye on the clouds. At 1715 MST, as sunset approached, I took this photo of the western sky:

As can be seen, there were large holes in the cloud cover so I had hopes of being able to image the next ISS pass. I still had the telescope and D7000 pointed at the moon and this is what the view to the east looked like shortly after ISS moon transit:

I parked the telescope and powered it off at 1724 MST, and left the observatory (it was cold). I returned to the observatory at 1805 MST and powered the telescope back up. I updated the ISS TLE in the AutoStar for the night's pass. Then used the moon for a focus test with the D7000 DSLR at prime focus. Used Jupiter for a finderscope alignment check. I then began waiting for the ISS pass to occur. Clouds along its path would make things interesting.

I started recording at 1835 MST, just prior to the ISS rising above the trees. Clouds made picking it up difficult but I finally did. I had to make a large pointing correction but after that, tracking was fairly good. The ISS played "hide-n-seek" with some clouds during the pass. But I managed to get a 6m13s video recording. I would have to do a frame-by-frame check of the video to see how well the ISS was imaged.

1850 MST: took a quick look at Jupiter, low in the east, at 77X. The four Galilean Moons were visible, as was the Great Red Spot. Seeing was not good due to thin clouds and the low altitude. I then took a quick look at the moon at 77X.

I did the ISS video post-processing Tuesday morning. (By the way, there is no doubt that winter is on the way. As I was checking the video about the time of sunrise, the temperature outside dropped to 29°F.) I studied the moon transit video frame-by-frame. And I GOT IT!!!! The transit occurred about 2 seconds ahead of the predicted time. Here are three frames from the 2 second video, showing the ISS just before the transit (the ISS is on the right), mid-transit, and after the transit (on left). The insets show a cropped version of the ISS from that frame.

What surprised me from the video was that the ISS was so bright it was not silhouetted against the bright moon. I had expected the ISS would be a black silhouette. But as seen in the middle image above, the ISS appeared bright as it crossed the moon. The images are not very clear due to the thin clouds and the moon's low altitude at the time of the transit.

To view the full 2 second video and see the ISS pass from the lower right to the left, click the image below. Once the video loads and runs, you may want to manually scrub back and forth to view the ISS transiting the moon.

For those using Firefox and can not get the video to load, or if you want to view the full-size HD video, I have made it available here:

So, now I'm happy! I captured an ISS moon transit! (I will be sending a donation to CalSky for their efforts. Thanks CalSky!).

So, what about the night's second ISS pass? There were some good frames although due to the low altitude, clouds, and the "line-of-sight" distance to the ISS, the images were not very clear. However, as seen in the three cropped captures below, the solar panels are visible:

But more magnification is needed for best results. I will return to ISS imaging at prime focus + 3X TeleXtender on the next ISS pass opportunity.