🌠 #17: Return to M42 – Orion Nebula

Posted on by admin

🔭 A Dedicated Night for a Stellar Jewel

This time, I followed my own advice: one target, one night. No distractions, no side quests — just M42, the Orion Nebula.

In the previous session, I had gathered 32× 60s subs, but the result was noisy and lacked depth. So I returned with a clear mission: collect more data, match the framing precisely, and create my first multi-night composite.

This was a new kind of challenge. Instead of just framing a beautiful object (as I did with M31), I had to replicate a previous framing down to the pixel — so that both datasets could align properly during stacking. The hard part? My mount tends to drift slightly over time, so I had to refocus, reframe, and check alignment between each run. Once I felt confident in the match, I hit “Run.”

To keep things consistent, I reused the exact same camera settings as before:
60s subs at ISO 400, captured at about -3°C.

đŸ§Ș Image Processing

I started by reviewing all light frames from both sessions. Fortunately, the ambient temperature between the nights differed by only about 3°C, so my darks and bias frames worked well across the board.

Unfortunately, the framing wasn’t perfect. The second night had a slight offset. I decided to merge the datasets anyway, not wanting to crop out nearby structures like the Running Man Nebula or the delicate tendrils of gas on the right side of M42.

This introduced a side effect: a visible gradient stripe across the merged frame — an area where light was from one night, but calibration was applied from both. I used layer masks to locally correct it by selectively brightening the affected area. Some gradient remained, but in my eyes, the improvement in signal-to-noise ratio (SNR) more than justified it.

I briefly tried processing the second night’s data in isolation — but the added depth of the combined set was undeniable. So I pressed on with the full 2h 37min dataset.

📾 Two Versions

Version 1:

This is the fully processed, desktop-stacked version — combining both nights of data. It’s clean, balanced, and shows fine detail throughout the nebula.

Version 2:

M42 – 2h 37min @ ISO 400, 60s subs, -3°C
Final version (stacked & masked)
Smartphone edit (saturated & “popped”)
Noise vs structure: comparing 30 min vs 2.5 h

My “smartphone” version — reprocessed entirely on my phone using a set of sliders. I bumped saturation and cranked up the contrast using a so-called “pop” slider. The core is blown out, the highlights are exaggerated — but it’s bright and striking, perfect for showing non-astro friends when they ask what all this late-night sky stuff is about. 😄

📊 Conclusions

Can you improve your deep-sky image by adding a second night of data?
Yes. Absolutely. Without question.

Comparing the earlier M42 version (just ~30 minutes) to the new ~2.5-hour composite reveals major gains:

  • Lower noise means fainter structures become visible.
  • The contrast between cloud layers can be more aggressively stretched.
  • Fine details once hidden in the noise now emerge with clarity.
  • What was once pixelated becomes smooth and textured.

More data means more flexibility in post-processing — and that means more beauty.

Worth every single minute under the stars.

Clear skies,
Chris