Intermediate Spiral Galaxy in Ursa Major

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NGC3184 is an intermediate spiral galaxy, visually located within the constellation Ursa Major. It is generally said to be about 40 million light years from us; at that distance, it would be about 100,000 light years across, which is somewhat less than the size of our Milky Way galaxy, but large for galaxies; its distance from us makes it look small. Compare this to M33, which is little more than half the actual size of NGC3184, but NGC3184 is about 15 times as far away from us as is M33. NGC3184 presents to almost directly face-on, giving it a dramatic appearance.

This galaxy is remarkable mostly for the frequency with which there have been observed supernovae, which is much greater than would be expected.

The gathering and processing of this data-set was complicated by the presence of two extremely bright stars near the galaxy; the bright yellow star to the right of the galaxy in the uncropped version (mag 6.5), and one just off the frame at the upper left (one of the bright stars in the asterism the Big Dipper). As always, it's fun to scan the background of the uncropped image, and see all the tiny galaxies hundreds of millions of light years away; the largest is NGC3179 (at the bottom of the uncropped image, close to the lower left corner), a magnitude 13.1 lenticular galaxy approximately 334 million light years from us; at that distance, it is a very large galaxy--close to 200,000 light years across.


Technical Information:

(HaL)(HaR)GB: 480:740:320:240:240 (a total of almost 34 hours of exposures); luminance layer consists of blend of 37 twenty-minute images using a luminance filter; R channel is a blend of 16 twenty-minute images using a red filter, and 24 twenty-minute images using an Ha filter; G consists of 12 twenty-minute images taken through a green filter, while B is the combination of 12 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 (using NormalizeScaleGradient) in Pixinsight. Color combine in Pixinsight. Ha data blended into the color layer in Pixinsight. Some post-processing (background neutralization, color calibration, gradient removal, Multiscale Linear Transform for noise reduction and later for sharpening, done in Pixinsight; some finish work (LRGB combination, 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 February and early March of 2022. Image posted March 30, 2022.

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

Seeing: Generally excellent, with individual calibrated luminance images having FWHM varying from .9 to 1.7 arcseconds.

CCD Chip temperature: -25C

Copyright 2022 Mark de Regt

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