NGC 4631 – Whale Galaxy
NGC 4631 – The Whale Galaxy
This was a project I worked on over several nights in May 2016. I began by shooting short exposures during the waning gibbous moon phase, capturing light frames with heavy moon glow. As the days went on, and clear nights continued, my exposure time increased. I kept attacking this galaxy night after night, adding about an hour’s worth of good data each time. The contrast in my images continued to improve each night as I got closer and closer to new moon. This is the result from almost 4 hours of exposure. It was actually quite an enjoyable experiment to add an extra hour at a time, stack the data and process. As the signal to noise ratio increased, the details of the galaxy emerged through processing.
Total Exposure: 3 hours, 52 min. (76 frames)
Astrophotography Processing Tips
The most challenging aspect of processing this image was not the galaxies small size, it was the large area of black space in the frame. When you photograph a deep-sky object containing large areas of empty black space you must pay special attention to noise reduction and gradients. Gradients and vignetting are major issues to tackle when imaging from my light polluted backyard in the city. Even though the signal to noise ratio improved as I stacked more exposures together, a heavy gradient with wavy discoloration remained throughout the image. Once again, the Gradient Xterminator plugin for Adobe Photoshop was a life saver. I ran several iterations until I was able to achieve a consistent black-point of about R:18, G:18, B:18)
The Whale and Hockey Stick Galaxies
About the Whale Galaxy
NGC 4631 is an edge-on galaxy similar in size to our own Milky Way, located in the constellation Canes Venatici. The Whale Galaxy has a small, yet bright, companion galaxy classified as NGC 4627 near it’s core. This galaxy is difficult to observe visually in small telescopes as I experienced first hand! This interested deep-sky object has been well photographed by amateur and professional astronomers alike.