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NGC 4631 – Whale Galaxy

NGC 4631 Whale Galaxy

The Whale Galaxy in Canes Venatici


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.

Astrophotography Details:

Total Exposure: 3 hours, 52 min. (76 frames)

Imaged May 24, 26, 30, 31.
May 24 – 150s ISO 800
May 26 – 180s ISO 800
May 30 – 180s ISO 1600
May 31 – 210s ISO 1600


Stacking multiple nights in Deep Sky Stacker

My stack of 4 night’s worth of frames in DSS

Camera: Canon 450D (modified)
Telescope: Explore Scientific ED80
Mount: Skywatcher HEQ5 Pro
Guide Scope: Orion Mini 50mm
Guide Camera: Meade DSI Pro II
Acquisition Software: Backyard EOS, PHD Guiding
Processing: Adobe Photoshop CC, Noel Carboni’s Tools


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)


View the Equipment I use to Photograph Deep Sky Objects


The Whale and Hockey Stick Galaxies

Whale Galaxy and Hockey Stick Galaxy

Wide field photo using an 80mm telescope of 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.


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