Eagle Nebula Captured Over 5 Nights from Light-Polluted London

Capturing the cosmos can be a challenge, especially when your backyard is bathed in the harsh glow of city lights. But for dedicated astrophotographers, even Bortle 9 skies in London can yield spectacular results. This post delves into the journey of capturing the iconic Eagle Nebula over five summer nights, showcasing the power of advanced equipment and meticulous processing.

The Challenge of Light Pollution

London's notorious light pollution presents a significant hurdle for astrophotography. The pervasive artificial light washes out fainter details and degrades image quality. However, with specialized filters and careful planning, it's possible to overcome these limitations and reveal the hidden wonders of the universe.

Equipment Arsenal

The following equipment was instrumental in this project:

• Telescope: Askar 120mm Apo Triplet
• Filters: Antlia 2nm SHO filters, Optolong RGB
• Filter Wheel: ZWO Filter Wheel
• Mount: Skywatcher EQ6-R Pro
• Camera: ZWO ASI2600MM Duo Pro (cooled)
• Controller: AsiAIR Plus
• Guiding: William Optics guide scope with ZWO ASI120MM

Data Acquisition

A total of 791 exposures, each 30 seconds long, were gathered over five nights. This extensive capture session included both narrowband (SHO) and broadband (RGB) data to accurately represent the nebula's structure and color.

• Narrowband Exposures: Essential for isolating specific emission lines of hydrogen, oxygen, and sulfur, crucial for detailing nebulae.
• RGB Exposures: Used to capture the star colors and provide a more natural overall appearance.
• Calibration Frames: Bias, sky flats, darks, and flat darks were meticulously captured to remove sensor noise and optical artifacts.

The Art of Processing

Processing is where the magic truly happens, transforming raw data into a stunning image. The workflow involved:

• PixInsight: This powerful software suite was used for:

  • Weighted Batch Preprocessing (WBPP): For initial calibration and stacking.
  • GraXpert: To address gradients in the SHO data.
  • MS G: For combining RGB stars.
  • BlurXterminator, NoiseXterminator, StarXterminator: For targeted noise reduction and star removal.
  • Narrowband Normalization: Ensuring consistent color balance across the SHO layers.
  • Stretching: Applying different stretching techniques (statistical for SHO, star for stars) to reveal faint details without clipping.

• Photoshop: Used for the final touches:

  • Merging Starless and Stars: Combining the processed nebula with the star data.
  • Color Balance and Saturation Adjustments: Fine-tuning the hues and vibrancy.
  • Final Optimization: Preparing the image for viewing on various devices, including mobile.

A Testament to Perseverance

This image of the Eagle Nebula is a testament to the dedication and skill required in modern astrophotography. By leveraging advanced technology and sophisticated processing techniques, even the challenges of light pollution can be overcome to bring the wonders of the cosmos into view.

Technical Note on Calibration Frames

A question was raised regarding the use of both bias frames and dark flats. While both serve to calibrate data, their specific roles can be nuanced. Bias frames correct for read noise, while dark flats are specifically designed to remove thermal noise from flat frames. In this case, using both likely aimed to provide the most comprehensive calibration, ensuring maximum detail and signal-to-noise ratio, though careful experimentation with one or the other might reveal subtle differences in the final output, particularly concerning black clipping.