International Space Station Solar Transit

The International Space Station transits the Sun passing by sunspot group AR2585. I made my monthly check for ISS transits near Austin this morning. There was a good possibility in just four hours with the sun shining brightly outside. After a quick lunch, Mary and I tossed the camera and scope in the car and headed north. Lots of clouds had moved in and we decided to head north-west to Briggs, Texas rather than north-east to Round Rock. We arrived in Briggs with about 15 minutes to spare with about 50% cloud cover. I took measure of the motion of the clouds and picked a spot to set up. Within seconds of the transit the sun was behind a cloud, but I finally have images of the ISS!

Questar 3.5 telescope with a Sony a6300 shooting 30 fps 4k video at prime focus from Briggs, Texas. Exposure 1/320 sec at ISO 200. 2016-09-04 19:15 UT. UHD 4k video frames deconvolved in Lynkeos, then composited and exposure adjusted in Photoshop.

Overall the ISS is roughly the size of a football field. It was about 300 miles away when these images were taken. Seeing conditions were not very good. Wind gusts were blowing hard enough to shake the scope a bit. This stack of the best 5 images shows some detail including the 8 long solar panel arrays along side the main modules.

The original 4k video, slowed down to half speed (in case you blink) is on Vimeo: ISS Solar Transit 4k Video

The following data is from ISS Transit Finder:

Sunday 2016-09-04 14:15:48.01 • Solar transit
ISS angular size: 61.34″; distance: 450.44 km
Angular separation: 1.3′; azimuth: 206.1°; altitude: 63.7°
Center line distance: 0.16 km; visibility path width: 4.57 km
Transit duration: 0.57 s; transit chord length: 31.6′
R.A.: 10h 56m; Dec: +06° 47′; parallactic angle: -21.8°
ISS velocity: 55.8 ′/s (angular); 7.31 km/s (transverse)
ISS velocity: 1.11 km/s (radial); 7.39 km/s (total);
Direction of motion relative to zenith: 110.0°
Sun angular size: 31.7′; 31.0 times larger than the ISS

ISS Transit Finder can make calculations up to seven weeks in advance. The ISS makes small orbital adjustments. It's best to recheck the ground track a few days before and a few hours before to get the most accurate estimate.

Content created: 2016-09-04

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