M31 Mosaic - Eight Frames of the Great Andromeda Galaxy
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An eight-frame LRGB mosaic of the Great Andromeda Galaxy — combining long-focal-length resolution with a wide enough field of view to capture the whole galaxy in one frame. Earlier attempts at this object are also on file: a three-panel mosaic from 2005, and even earlier images from 2004 and 2003.
Location: Taken remotely from Grapevine, Texas using the Conley Observatory at the Comanche Springs Astronomy Campus near Crowell, Texas
Temperature: 90 - 92 degrees F
Date: August 2019
Scope: 12.5” RCOS Ritchey-Chretien
Mount: Software Bisque Paramount ME
Cameras: FLI Proline PL-16803 astronomy camera and Nikon D810a (for a small amount of color)
Exposure Info: Eight-frame LRGB mosaic for the grayscale data, taken with the PL-16803 unbinned. Approximately 16 hours total luminance. Color data taken mostly in five RGB frames covering the galaxy disk, each frame averaging 2.5 hours for approximately 12.5 hours of total RGB color. A small part of the color was borrowed from a Nikon D810a image taken the previous year (36 minutes using a small Tak FSQ-85ED apo refractor).
Total Exposure Time: Just over 29 hours!
Processing of Grayscale Frames: Calibration, star alignment, and integration of individual frames done within PixInsight. Each frame received Multiscale Linear Transform, Dynamic Crop, Histogram Transform, Local Histogram Enhancement, and HDR Multiscale Transform in PixInsight. Grayscale frames were assembled in PixInsight using the Gradient Merge Mosaic process. Noise reduction and local contrast enhancement were performed in Photoshop CC (using ProDigital Actions) on the full mosaic grayscale frame.
Processing of Color Frames: Calibration, star alignment, and integration of individual frames done within PixInsight. Each frame received Multiscale Linear Transform, Dynamic Crop, and Histogram Transform in PixInsight. Color frames were brought into Photoshop CC and aligned, frame by frame, with the grayscale master frame. Color frames were balanced, heavily saturated, cleaned of noise (a variety of techniques), and blended with the luminance data using Color blending mode. Additional color for background stars not covered by the mosaic frames was added in Photoshop CC using the Nikon D810a image taken the previous year.
About this Image
Shooting a mosaic, especially an eight-frame color LRGB image, is not for the faint of heart! But every now and then we astrophotographers get the urge to push our skills and our equipment. The result of such mosaics, like this one of the very familiar M31, Andromeda Galaxy, is to achieve fine resolution (detail) as delivered by long-focal-length optics with the wide field of view typically given by shorter focal length scopes and lenses.
Meaning? A huge galaxy such as Messier 31, Andromeda’s catalog designation, can be captured completely, yet in terrific detail.
This galaxy (found within the constellation Andromeda) isn’t the closest galaxy to us, but it’s pretty close — only 2.5 million light years away. That’s 1.47 x 10^19 miles, if you need that perspective. As pictured, you could fit 7 or 8 of our moons across the disk of this galaxy from our sky perspective. It’s huge, and it’s a naked-eye object in most rural-to-suburban skies.
Oh, by the way — any star you see in this image (click on it to zoom in) is in our own Milky Way galaxy, since we have to look through our own neighborhood to see the next one over. Stars in Andromeda are too small to resolve from this distance, though you can make out clusters of them together, especially the globulars that have their own designations.
How many stars are there in Andromeda? You’re looking at about a trillion stars, give or take a couple — about 4 or 5 times the number in our own galaxy.
One of the more intriguing aspects of M31 is that the light captured here first left that galaxy around 2.5 million years ago. In other words, looking into the sky is about as close to actual time travel as we can experience.
Objects in this Image
M31’s two brightest Messier companions, its most prominent star cloud, and its brightest resolvable globular clusters are all identifiable in this mosaic. Drag the slider below to reveal them in order of brightness.
M32Galaxymag 8.1M110Galaxymag 8.1NGC 206Star CloudBol 338Globular Clustermag 14.2Bol 23Globular Clustermag 14.2Bol 225Globular Clustermag 14.2Bol 158Globular Clustermag 14.7Bol 218Globular Clustermag 14.7Positions plate-solved via astrometry.net. M32 and NGC 205/M110’s identities and apparent (V-band) magnitudes are from the SIMBAD catalog, as are the five brightest resolvable globular clusters actually within this frame (Bologna catalog designations; SIMBAD lists over 600 catalogued globular clusters in this field, only the brightest confirmed few are labeled). NGC 206, the large star cloud near M31’s southwest arm, has no published point magnitude — it’s revealed alongside M32 and M110 rather than placed by brightness. Drag the slider to reveal each object’s name, brightest first.