Spiral Galaxy in Pegasus

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NGC7217 is a flocculent spiral galaxy high in the nothern sky in late summer, into the winter, about 50 million light years from us. While there is an obvious sprial structure, there are no spiral "arms" like one often sees in a sprial galaxy.

It has a series of three visible ringlike zones: a nuclear ring 21 arcseconds/5,000 light years in diameter (the very brightest part in the center of the image), a weak inner ring 63 arcseconds/15,000 lighte years in diameter (the yellow part outside of the innter ring), and an outer ring about 3 arcminutes/43,000 light years in diameter (about a third of the diameter of our Milky Way). The origin of the ring features is uncertain. It is surmised that this unusual structure may be the result of one or more mergers with other galaxies.

This photo shows the significant halo around the disc of the galaxy.

The entire field of the uncropped version of the photo is about the same width as a full moon.


Technical Information:

LRGB: 900:180:180:280 (a total of almost 26 hours of exposures); luminance layer consists of blend of 26 thirty-minute images and 24 five-minute images (all using a luminance filter; R channel is a 12 fifteen-minute images taken through a red filter; G consists of 12 fifteen-minute images taken through a green filter, while B is the combination of 14 twenty-minute images taken through a blue filter.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chrétien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 with internal filter wheel (SBIG filter set), guided by an SBIG AO-X/STX Guider, all riding on a Bisque Paramount ME German Equatorial Mount.

Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X.

Processing: All images calibrated (darks, bias and sky flats), aligned, and combined in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, deconvolution, gradient removal, HDR Multiscale Transform, Multiscale Linear Transform for noise reduction and sharpening) done in Pixinsight; some finish work (Neat Image noise reduction, LRGB combination, contrast and saturation adjustment) was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights during October, November and December of 2021. Image posted December 3, 2021.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Variable, with individual luminance images having varying FWHM from 1.7 to 2.5 arcseconds.

CCD Chip temperature: -25C

Copyright 2021 Mark de Regt

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