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Our sun: H-alpha and CaK collage | by Tommi R
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Our sun: H-alpha and CaK collage

A collage utilizing both H-alpha and CaK imaging of our Sun. Subframe positions is "artistic" and does not represent correct orientation compared to Sun - all images are however taken by me excluding the Apollo era (free) picture of Earth showing approximate scale. Pictures taken in southern Finland during summers of 2016 and 2017 as I haven't had time to image at all lately.


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Recorded with BW ASI178mm camera, colors added in post production. H-alpha images colored to red and yellow and they are partially inverted to pop out surface details, protuberances and filaments. CaK is colored to blue to mimic imaging bandwidth for CaK.


H-alpha: 656.28 nm (deep red in reality) hydrogen line. Tunable wavelength. Exposure times around 2 ms.

CaK: About 8 nm wide bandpass at the Calcium II K-Line centered around 395 nm (ultraviolet). Exposure time of about 0.8 ms.


Prefilter: Baader D-ERF (with H-alpha), Baader AstroSolar film (with CaK)

Scope: TS Express 80/480 mm FPL53 APO

Filter: Daystar Quark or Baader CaK

Camera: ASI 178mm with 0.5x reducer

DIY Arduino based focuser motor control

Mount: Celestron AVX (equatorial mount), StarAdventurer


Software: FireCapture, SharpCap, Autostakkert!, ImPPG and Photoshop CC.


Typically stacked a best few percents of 5000 images to create each of the separate photos. Full disk H-alpha sun is a composite of several sub images. I roughly estimated that I collected about 180 000 frames and 775 GB of uncompressed AVI video as raw material. Final stacked image number should be close to 4000 in that composite.

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Uploaded on February 25, 2019