Caldwell 49, the Rosette Nebula. It is a large, star forming nebula with approximately 2,500 young stars. The Rosette is located in the constellation Monoceros, the unicorn, 5,000 light years from Earth. It is roughly 130 light years in diameter. It is also the official astronomical object for the state of Oklahoma, a fact you can use to impress strangers.
The Rosette Nebula is fairly easy to locate. It is one point of a triangle with the stars Alnatak (the eastern-most star in Orion’s Belt), and the star Betelgeuse (Orange star to the east of Alnatak) making up the other two points. The central star cluster is visible in binoculars. It is a popular target for Astrophotography.
It has taken a while for me to get an image of the Rosette Nebula I am satisfied with. One of my earlier images is below, an RGB image taken with a DSLR.
When I acquired a mono astro-camera I knew I wanted to good shot of the Rosette Nebula. I decided on narrowband imaging to better pick up the nebula emissions. This would be a Hubble Palette image, using Sulfur for red, Hydrogen-alpha for green, and Oxygen for blue. Images in this palette typically have more of an orange/blue coloring.
The data was gathered using the setup shown. The lens is a Canon 100-400mm f/4.5-5.6L IS II. It is connected to an Astromechanics auto-focus adapter allowing me to adjust focus as it changes through the night. A motorized filter wheel is next followed by the monochrome astro-camera, an ASI1600mm. Next to the main setup is the guide scope, attached to an ASI120mm-s guide camera. The guide camera follow a star throughout the night, sending small adjustments to the mount to make sure the target remains centered throughout the imaging session. The imaging setup is on top of a Skywatcher EQ6r-pro mount that moves with the rotation of the earth throughout the night. The equipment is attached to a Raspberry Pi (RPi) computer attached to the scope. The RPi communicates with the equipment, and I can control the RPi remotely from a laptop inside using the open-source platform KStars/Ekos. The additional boxes seen are batteries to power the equipment overnight.
The final image was taken over 3 nights, one night for each filter. It consists of 58 Ha images, 39 OII images, and 50 SII images. Each image is 300s, approximately 12 hours total imaging time. The images were brought into PixInsight (PI), an imaging program designed for astrophotography. They were stacked and combined, then edited to bring out the detail, creating the final image.
ASI1600mm, Canon 100-400mm f/4.5-5.6L II
SII – 250 minutes, Ha – 290 minutes, OIII – 195 minutes
