Imaging Orion in mosaic mode, HaRGB
A project with a long history
October 25th, 2024Probably as long as I can remember, and particularly since I began my journey observing the sky, the first constellation that definitely caught my attention was the mythical figure of the giant Orion who, followed by his two faithful dogs, fights defiantly against the Bull and everything that comes into his sight. The figure of the hunter is delicately outlined by the bright stars that form the constellation that, unlike the vast majority of figures in the sky, really resembles what its name says.
I remember drawing Orion while observing it with the naked eye from the terrace of the building where I lived in the city of Santiago de Chile. Everything happened when I was 15 years old and, the more times I drew it, the more details appeared and I even included the main deep sky objects, which I detected using a set of binoculars. To this day I still have those drawings and every time I see them, a series of emotions and beautiful memories come to my mind of those warm summer nights in the southern hemisphere under the stars of Orion.
It strikes me to think that I came to form such a special and close relationship with Orion that when that time of year inevitably came when the Sun entered its domain and hid it under its powerful brightness, I counted the weeks I had to wait to see it rise again at dawn.
Beautiful memories that gave rise to my lifelong passion for systematic observation of the sky, either with the naked eye or with simple instruments. In fact, Orion fueled the motivation that led me to begin dreaming of the idea of one day being able to photograph it instead of simply drawing its shape in the sky.
And that desire to photograph Orion finally materialized when I became a member of the Chilean Association of Astronomy and Astronautics (ACHAYA) in 1986, the year of the mythical Halley's Comet. At this institution, I had access for the first time in my life to an astronomical observatory with instruments that allowed me, among other things, to learn analog photographic techniques both in data acquisition and its subsequent development process. Since that time, I was able to capture the light of Orion using 35mm film initially and then using the NASA Astrograph which used Kodak photographic plates.
A lot of history and observations have passed since that distant 1986 and my fascination with Orion became a true support for my passion for astronomy which remains current to this day. And in one way or another, I always had in mind to make an image of Orion again but using current technologies both in the acquisition and in the processing of data.
This is how this project was born, which resulted in the image that we present here as Cluster One Observatory.
The image of the Orion constellation is the final product of a 9-panel mosaic involving more than 100 hours of observations obtained between December 2023 and February 2024. The observations were made from the Atacama Pathfinder EXperiment - APEX control center in San Pedro de Atacama, Chile. This observing site has grade 2 on the Bortle scale. For this project, the Rokinon 135mm f/2.0 ED UMC lens was used coupled to the ZWO ASI294MC Pro sensor and a ZWO AM5 mount. Total control of the data acquisition was, as always, in charge of the ZWO ASIAir Mini unit. Finally, the Optolong L-Extreme (narrow band) and OptoLong UVIR Cut (Broadband) filters were used, mounted on a ZWO automatic filter wheel. In the panel that includes the M42 area, an HDR composition was made with exposures of 5, 10, 15, 30, 60, 120 and 300 seconds in both filters, in such a way as to rescue the weak structures without saturating the core.
Taking into account the complexity of this project, a series of programs written in Python were developed to maintain the homogeneity of the observations in each panel and filter. The program automatically stores the header of each of the FITS files in a database, with the objective of censusing the frames by panel and filter, suggesting the observation strategy so that all panels and filters have similar integration times, in such a way as to avoid gradients and several other problems that arise when making mosaics of these characteristics.
Last but not least, "Cluster One Observatory" is a family project, and we want to dedicate this work to
Santiago Mac Auliffe Contreras, who on the day of the publication of this image, October 25, 2024, turns 31 years old.
Santiago gave my life the direction and meaning it needed when he was born, illuminating everything around him to this day.
We love you so much dear Santiago… Happy birthday!
www.clusteroneobservatory.com 
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