ISS Transit Across the Sun: A First-Time Astrophotographer's Success

Last week, I stumbled upon a photograph of the International Space Station (ISS) transiting the Sun. Intrigued, I decided to see if I could replicate this captivating celestial event. A quick check on revealed an opportunity right in my own backyard, scheduled for today!

The Preparation

With my Celestron NexStar Evolution 8” EdgeHD telescope, Baader Digital Solar Filter, and Canon EOS R5 Mark II ready, I set my sights on the Sun. After careful focusing and admiring the sunspots, I waited for the precise moment. One second before the predicted transit time, I initiated continuous shooting.

The Moment of Transit

And then, it happened! The ISS, a tiny silhouette against the brilliant solar disk, became visible. The accuracy of the prediction was astounding. Despite the heatwave causing atmospheric turbulence, I managed to capture the event. This was my very first attempt at such a challenging capture, and I'm thrilled with the results.

ISS transiting the Sun

Technical Details

Sun & ISS Data:

Date: 12.08.2025
Time: 07:01:40 UTC
ISS angular size: 32.46"
Transit duration: 1.36s

Equipment:

Telescope: Celestron NexStar Evolution 8” EdgeHD
Filter: Baader Digital Solar Filter OD 3.8
Camera: Canon EOS R5 Mark II

Acquisition Details:

Focal length: 2032mm
Focal ratio: f/10
Frames: 215 (41 with ISS)
Shutter speed: 1/8000s
ISO: 400

Location: My garden, Illnau, Switzerland

Processing Steps

Adobe Lightroom Classic: Exported CR3 files to TIFF.
AutoStakkert!4: Stacked the best 75% of frames.
RegiStax6: Applied wavelet sharpening.
Adobe Photoshop:
- Layered all frames containing the ISS.
- Masked the ISS.
- Combined into a single image.
- Desaturated.
- Adjusted brightness/contrast with curves.
- Applied selective color curves for a vibrant solar appearance (artistic choice).
Adobe Lightroom Classic: Cropped and performed final adjustments.