Capturing the Andromeda Galaxy: A Backyard Astrophotography Journey

Embarking on a journey to capture the cosmos from our own backyard is a rewarding experience, and the Andromeda Galaxy (M31) is a particularly stunning target. This post delves into the detailed acquisition and processing steps that brought this breathtaking image to life, all from a Bortle 5 location.

The Acquisition:

The foundation of any great astrophoto lies in its acquisition. For this shot of Andromeda, the following setup and parameters were used:

• Sub-exposures: 450 frames at 30 seconds each
• ISO: 1600
• Calibration Frames: 50 dark frames, 50 flat frames, 50 bias frames
• Location: Bortle 5 Backyard
• Equipment:
  • Star Adventure unguided tracker
  • Canon 60D camera
  • 70mm Refractor telescope

An interesting point raised in the original discussion is the unguided nature of the tracking. While the star tracker adjusts for Earth's rotation, it doesn't have a dedicated guiding scope to self-correct for drifts. Fortunately, at the focal length of the 70mm refractor, exposures of up to 45-60 seconds can often be achieved without noticeable star trailing, allowing for a substantial dataset to be collected.

The Processing Pipeline:

Achieving the final polished image involves a multi-stage processing workflow, utilizing powerful software to bring out the details and colors of Andromeda:

1. Stacking and Cropping: The raw frames were stacked using Siril. This crucial step combines all the sub-exposures, reducing noise and enhancing the signal-to-noise ratio. The image was then cropped to focus on the galaxy.
2. Initial Cleanup and Denoising: GraXpert was employed for background extraction to remove any unwanted gradients or light pollution, followed by denoising to further clean up the image.
3. Advanced Calibration and Enhancement in Siril: The processing continued back in Siril with several key steps:
   • Photometric Color Calibration: This helps in achieving accurate and natural colors.
   • Green Noise Removal: Addresses a common issue in astrophotography data.
   • Star Removal: Temporarily removing stars to better process the nebulosity and galaxy core.
   • Histogram Stretch: Gradually increasing the dynamic range to reveal faint details.
   • Star Recombination: Reintroducing the stars back into the image.
4. Final Touches in Photoshop: The journey concluded in Photoshop, where final color adjustments and curve modifications were made to enhance the overall contrast, bring out the galaxy's structure, and achieve the final artistic vision.

This comprehensive approach, from careful acquisition with relatively simple equipment to a multi-stage processing workflow, demonstrates how stunning deep-sky objects can be captured and refined from modest observing locations.