Cassiopeia Observatory

iPhone 5s Captures Chinese Space Station
Tiangong-1 Transiting the Sun!
Posted: 25 September 2013

The observatory was opened Wednesday, 25 September 2013, at 0834 MST, 71°F, to clear skies. CalSky.com had alerted me that the Chinese space station Tiangong-1 would transit the sun this morning at 095048 MST. I decided I would try to capture it using my new Apple iPhone 5s using the slo-mo video recording. I went to the observatory early in order to do some test photographs and video recordings of the sun.

I commanded the telescope to GOTO the sun using the "Sun as Asteroid" technique. At 0843 MST, observed the sun, 83X. One nice sunspot (AR1846) and a small sunspot group (AR1850) were visible. I then began setting up for imaging of the sun. I attached the iPhone 5s to the telescope using my homemade afocal adapter with a 26mm eyepiece (77X). Apple iPhone earbuds were used as a remote shutter release. I did some still and slo-mo video recordings as a test for focus, framing, and exposure. At 0907 MST, I took this afocal photograph of the sun showing the sunspots:

The above full-frame photograph does not quite show the entire solar disk. The slight curvature at the top is from the edge of the eyepiece field-of-view.

Here is a closeup of the sunspots, cropped from the full resolution version of the above photo:

All was now in readiness for the transit. CalSky.com predicted this path across the sun:

The Tiangong-1 space station is about 10 meters by 3 meters in size and would be 510.4 kilometers from my observatory at the time of the transit. The station would have an angular diameter of 4.4 arcsec. Yes, that's small.

I began slo-mo video recording with the iOS 7 Camera app on the iPhone 5s at 095015 MST and continued it for one minute to ensure that I captured the space station.

During post-processing of the video I discovered that the Tiangong-1 was successfully imaged on several frames as it crossed the sun's disk. This image from about mid-transit shows the space station, with the inset showing a magnified view:

If you can't find Tiangong-1 on the image, roll your mouse over the image or tap on the image (touchscreen) to see labels. As before, only the southern portion of the solar disk is visible in the image.

You can download a video to watch the Tiangong-1 space station cross the sun. I recommend you download the file and then step through the video frame-by-frame to watch the transit occur. In realtime, the space station crossed the sun in 0.59 seconds.

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