Clear nights in winter, in the great state of Missouri, are not really a thing of frequency
January 27th 2023 astrophotography adventure from the front yard, with a Bortle Sky rating of 8 – near the upper limits of the light pollution scale.
This is my first attempt at this target. The Rosette Nebula is a vast emission nebula located about 5,200 light years away. For observers and amateur astrophotographers in the northern hemisphere, the Rosette Nebula is a winter target. From mid-northern latitudes, the most favorable time to capture this nebula, which is also cataloged as Caldwell 49, is during the months of January and February. The nebula reaches fairly high in the Northern night skies and that helps with transparency. Objects that are low on the horizon can create headaches for amateur astrophotographers in the city due to heavy sky glow and atmospheric turbulence.
The Rosette Nebula is a “beautiful” target, enveloped in colorful hydrogen gas and at its core an open star cluster (NGC 2244).
The star-forming region lies near a large molecular cloud in the constellation Monoceros, the Unicorn. It is closely associated with the young open star cluster NGC 2244. Also known as the Satellite Cluster, NGC 2244 appears in the centre of the Rosette. The hot young stars of the cluster were formed from the nebula’s material in the last 5 million years.
The stars in the Satellite Cluster are responsible for the nebula’s glow. Their radiation ionizes the surrounding clouds of nebulosity, causing them to emit their own light. The nebula glows in the red part of the spectrum because the powerful ultraviolet radiation from the stars strips electrons from the nebula’s hydrogen atoms.
The Rosette Nebula is a very active stellar nursery. It is home to numerous Herbig-Haro objects and Herbig Ae/Be stars, Bok globules, T Tauri stars and clusters of newly formed stars. The dark filaments of dust extending toward the centre of the nebula sometimes called “elephant trunks,” are shaped by the stellar winds and radiation from hot young stars and electromagnetic forces.
It spans 130 light years and has an angular size of 1.3 degrees. It is much larger than the better-known Orion Nebula, which is about 24 light-years across. However, the Orion Nebula is much closer to us at 1,344 light years and appears brighter but smaller than the Rosette.
Having an estimated mass of about 10,000 solar masses. It is home to about 2,500 stars. The most massive O- and B-type stars power the nebula and causes it to expand. The nebula will disperse in the next few million years, leaving behind only the central cluster, NGC 2244.
The Nebula was named after the stylized flower design used in sculptural objects since antiquity. The nebula’s appearance in optical light resembles the rosette. It is sometimes called the Skull Nebula because it also closely resembles the human skull.
The region of the Rosette Nebula contains several stellar groups in a range of 98 light-years (30 parsecs).
How to find the Rosette Nebula?
The Rosette Nebula is easy to find because it lies between two first-magnitude stars. It appears just south of the imaginary line that connects Betelgeuse in Orion and Procyon in Canis Minor. Betelgeuse is identified as the right shoulder of Orion (left from our point of view). It forms a prominent triangle with Procyon and Sirius, known as the Winter Triangle. Sirius in Canis Major and Alhena in Gemini can be used for orientation. The nebula lies just right of the imaginary line connecting the two stars.
Image Targeting and Image Settings
This is my first time imaging from a heavily light-polluted area, to neutralize the light pollution for a Bortle 8 sky, I deployed my Optolong L Ultimate filter – This is a 2″ 3nm dual band mounted filter designed to drastically reduce the effect of light pollution. The 3nm bandpass isolates the nebulae emissions into H-Alpha (red) and OIII (green-blue). It blocks light pollution, maximizes the signal from nebulae, and darkens the sky background. It also blocks artificial light from mercury vapor lamps, high and low-pressure sodium vapor lights, and unwanted natural light caused by the emission of neutral oxygen in our atmosphere.
I start the night off by levelling the tripod, then I roughly point one of the legs to the NCP (North Celestial Pole), add the mount to the tripod, the telescope to the mount and connect it all to my power supply. Next, I balance both the RA and Dec, and I wrap that up by locating Polaris and fine-tuning the mount, on both axes. I verify that all is correct by first verifying that no aircraft vicinity, and I use a laser pointer to true up my alignment.
Now the wait for astronomical twilight begins, this time of year is roughly at 645pm, but due to my location, I needed to wait until the city glow reduced, so that puts me at 700pm. During that time, I used my tablet and the AsiAir imaging system – to set up: a three-star polar alignment, image guiding, image preview, and the imaging sequence for the night.
My image settings for the night: The camera was cooled to -4° and the gain was set to 100. 30 x 60-sec EXP and 49 x 300-sec EXP – with Optolong L-Ultimate 3nm Dual Band.
I started imaging at 724pm and ended at 1217am. For the night my total exposure: 4.58 hours | Telescope: William Optics RedCat51 | Camera: ZWO 533MC Pro | Mount: Skywatcher GTi.
I am really gaining a deeper understanding of this software, it is pretty powerful. I stacked the 79 calibration frames for each (lights, darks, flats and bias), once they were all registered, debayered and registered. Since I had two exposures -60-sec and 300- sec processed as an HDR (not sure that this subject needed it, but due to the magnitude and the prominent stars, I figured why not).
I followed up with BackGroundNeutralzaion, Automatic BackGround Extraction, Color Calibration, and then star removal; which I will be adding back towards the end of processing the image.
As my comfort level grows, I attempted to process the image using the Hubble Palette technique. Named for an image processing technique done by the Hubble Space Telescope team, creates what is called “false color” imaging by using narrow-band filters and assigning the data captured with each narrow-band-filtered channel to one of the red, green, or blue colors in an RGB image.
Until the next adventure.
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