Cassiopeia Observatory

ISS-Moon Transit

Posted: 18 December 2013

Received a notice from CalSky about a transit of the International Space Station (ISS) across the nearly full moon on Tuesday, 17 December 2013, at 2253 MST:

The forecast for the night was not good. Sunset was pretty, as seen in this iPhone 5s photo:

Cassiopeia Observatory was opened at 2206 MST, 54°F. There were thin clouds over most of the sky. The just past full moon was visible high in the sky. At 2219 MST, took a quick look at Jupiter, 83X. The four Galilean Moons were visible on one side of the planet and the shadow of the moon Callisto was nearing the end of its transit.

I then began preparing to image the ISS-Moon transit. This photo shows the sky conditions near the moon at 2225 MST (28 minutes prior to the transit):

Jupiter is below and left of the moon. Sirius is at the bottom above the tree. In the original image the constellation of Orion is visible to the right of the moon.

This image of the moon, taken with the D7000 DSLR at prime focus of the 8" LX200-ACF, 1/250sec, ISO 100, shows a slight terminator:

I aligned the D7000 DSLR field-of-view on the moon to provide good coverage of the transit based on the CalSky prediction. I did a test HD video prior to the transit. At the time of the transit, thin clouds were passing in front of the moon. For this pass, the ISS was in the Earth's shadow so it would appear black against the bright moon. For the transit I used an exposure setting of 1/2000sec at ISO 3200. I began the HD video recording one minute prior to the transit and continued it for 90 seconds. During post-processing I discovered that the predicted transit time was 3 seconds early and the predicted path across the moon was slightly shifted. However, I still managed to capture the ISS crossing the moon's disk. This merged image from the video shows 15 images of the International Space Station during the 0.63 second transit:

This is an enlarged crop (upscaled 300%) of one video frame showing the ISS in more detail:

After the ISS-Moon transit was over, I did some observing of Jupiter at 222X. I monitored Callisto's shadow as the transit was nearing its end. The Great Red Spot (GRS) was also visible. The GRS appeared more red than I've seen it in recent years. Although thin clouds were passing in front of Jupiter, the details in the South Equatorial Belt near the GRS were well seen. Thicker clouds were approaching the moon and Jupiter by 2314 MST and the view of Jupiter was getting fuzzy. Decided to end the session.