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ISS Lunar Transit (2019Sep12)

ISS Transit on Sep 12, 2019 (UTC) ISS Transit on Sep 12, 2019 (UTC) ©2019 Frederick Steiling
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Target Information
Main Target Designation(s) ISS Transit of the Moon
Exposures
Date(s) of acquisition 12Sep2019 04:02:40 UTC
Location Defiance, MO
GPS 38°43'22.8"N 90°48'52.4"W
ISS Information
Angular Size 40.06″
Distance 689.82 km
Angular Velocity 33.5 ′/s
Transverse Velocity 6.72 km/s
Radial Velocity -3.11 km/s
Total Velocity 7.41 km/s
Moon Phase 95.7%
Capture resolution 1936x1216
Luminance (transit)
Video source 95" at 0.816ms / 47fps
Gain 55%
Stack (ISS) 7 frames, manually aligned on shadow
Luminance (surface)
Video source 120" at 0.816ms / 49fps
Gain 55%
Stack 1781 (30%) of 5937 frames
Red (surface)
Video source 120" at 2.550ms / 53fps
Gain 55%
Stack 1943 (30%) of 6475 frames
Green (surface)
Video source 120" at 3.204ms / 54fps
Gain 55%
Stack 1970 (30%) of 6567 frames
Blue (surface)
Video source 120" at 3.066ms / 50fps
Gain 55%
Stack 1802 (30%) of 6006 frames
Equipment
Imager ZWO ASI174MM
Filters ZWO 1.25" LRGB
Telescope/Lens Celestron C14 XLT SCT
Focal Length 3910mm (f/11)
Mount Celestron CGE Pro
Focuser Moonlite 2.5" CSL
Software
Acquisition FireCapture 2.5
Guiding None
Processing PIPP v2.5.9, AutoStakkert 3, PixInsight 1.8, Photoshop CC

To catch an ISS transit across the moon is to spend a lot of time planning where to set up and when to start clicking away with the camera.  Though they happen with fair regularly, these lunar transits are typically visible from a path only about 3.5 miles (5.6 km) in width that traces the earth's surface, and from the best vantage point at the center line, the transit itself still lasts less than 1 second.  Without a doubt, coming to the photo opportunity prepared is a must!

But as if a normal ISS transit wasn't uniquely difficult enough, the 11th of September this year presented an event that was both extraordinarily lucky and extraordinarily challenging.  This transit's path happened to fall right over ASEM's stationary observatory housing our C14 SCT, an excellent opportunity to get better detail than ever on the ISS with this "planetary cannon".  However, with great focal length comes great responsibility: With a field of view that covers only a fraction of the moon's surface, pointing the frame at a set of features that have been well analyzed to cover the ISS path requires care and precision!   In doing so, I was able to reveal the shadowed ISS across 7 frames and combined it with a full LRGB stack to present our space-faring friends in better detail than I've ever acquired!

The detail of the ISS is better than I've been able to acquire yet, and all this while it traveled in the shadow of the Earth.  Most prominently displayed and with some light detail are the flanking photovoltaic arrays with their supporting truss segments.  The Zvezda Service Module can be seen as a vertical shoot at the top of the station, and the large squarish portions at each side of center are the thermal control system radiators, largely hiding us from other detail at center due to the ship's tilted presentation toward the camera.

Once again, catching an ISS transit proved to be a remarkably exciting experience -- predicting the path, 90 minutes of setup and orientation, and several minutes hoping I was pointed at the right spot, all to see it zip across the live frame in tenths of a second!

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More in this category: « ISS Lunar Transit (2018Mar03)