M33 - The Pinwheel Galaxy in Triangulum (HaRGB)

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An LRGB plus H-alpha image of the Triangulum/Pinwheel Galaxy from Bortle 2 skies.

Location: Taken remotely from Grapevine, Texas at the Conley Observatory, Comanche Springs Astronomy Campus (CSAC), Three Rivers Foundation, Crowell, Texas

Date: November 21-22, 2017

Seeing: 6/10

Transparency: 9/10

Temperature: 24 to 42 degrees F (-30C on camera)

Equipment: 12.5” RCOS RC f/9 on a Software Bisque Paramount ME

Camera: FLI PL-16803 astro CCD camera

Filters: AstroDon Gen 2 Tru-Balance LRGB with 3nm h-alpha spectral band

Guider: Off-axis via MMOAG and SBIG STi camera

Exposure Info: LRGB plus Ha image; 250 x 10 minutes L; 12 x 5 minutes Red; 12 x 5 minutes Green; 12 x 5 minutes Blue; 6 x 15 minutes H-alpha (all color data binned 2x2)

Total Exposure Time: 8 hours 40 minutes

Processing Information: Acquisition in TheSkyX Professional. Calibration (darks, flats, & bias), Registration (StarAlignment), and Integer Rescale (to upscale RGB) in PixInsight. MultiscaleMedianTransform (wavelet noise reduction), Histogram Transformation, LocalHistogramTransformation, HDRMultiscaleTransform, and ColorCombination in PixInsight. LRGB combine, cropping, color balance, levels/curves, and sharpening (hi-pass) in Photoshop CS6. Color Blotch Reduction, Deep Space Noise Removal, and Local Contrast Enhancement in Photoshop via Noel Carboni’s Astronomy Tools Actions for Photoshop.

About this Image

Over 2.7 million light years away in the constellation of Triangulum. Known as the “Triangulum” or “Pinwheel” galaxy. It is of a grand spiral design, one of the largest galaxies in the night sky from our point of view, easily 1/2 degree across (the apparent size of our moon). M33 serves as a good test for truly dark skies—an easy naked eye object in magnitude 7 skies (Bortle 2) or better. The amazing number of visual HII regions, showing as reddish-pink in the image, is the key feature of this galaxy. Astrophotographers will often take extra h-alpha spectral band data (as I have also done) to add to the LRGB mix to make these regions “pop.” I used a bit more restraint in this regard than most, since the regular LRGB data showed them sufficiently enough for my tastes. Even so, the h-alpha data did serve to yield small amounts of detail in those areas, as well as a slightly darker red color.

HII Regions in this Image

A handful of M33’s brightest HII regions carry their own NGC/IC catalog numbers; drag the slider below to reveal them in order of brightness.

Normal image

Positions plate-solved via astrometry.net; region identities cross-matched against the SIMBAD catalog, otype HII, restricted to entries with a formal NGC/IC designation (the field also contains hundreds of fainter catalogued regions with only survey-internal designations, e.g. BCLMP/LGGS numbers, not labeled here). Apparent (B-band) magnitudes from the NASA/IPAC Extragalactic Database (NED). Drag the slider to reveal each region’s catalog name, brightest first.

🤖 AI-drafted · unverified

What it is: M33, often called the Pinwheel Galaxy (or the Triangulum Galaxy), is a face-on spiral and the third-largest member of the Local Group.
Constellation: Triangulum
Distance: ~2.73 million light-years
Apparent magnitude: 5.7
Angular size: ~70.8 × 41.7 arcminutes
Coordinates: RA 01h 33m 50s, Dec +30° 39′

This summary was generated by an AI assistant from general astronomical references, not from Jay’s own notes on this specific image. Treat every detail above as a starting point for research, not settled fact.