Moon
Moon - Click here for full resolution
The Moon is the well-known companion to Earth. It is by far the brightest object in the night-sky, and constantly changing. During its 28 day orbit around Earth, moon phases make it look different every day by the ever changing illumination by the Sun. So close to Earth, it is moving much faster than the other stars. It is the fifth largest moon in our solar system. The Moon is the only celestial object other than Earth where mankind ever set foot on and continues to be the subject of many spaceflight programs, both manned and unmanned.
Conditions
Images were taken on December 20, 2021 from the backyard in Groningen, The Netherlands (53.18, 6.54). At the time of observation, the Moon was at 97.6% illumination. It was visible on the Eastern horizon at an altitude of around 30 degrees.
Visibility charts showing 22:00h altitude throughout the year (left) and throughout the session on December 20, 2022 (right).
Weather was a bit cold, but generally good, with temperatures just below 0 degrees Celsius. Humidity was fairly low for this location at 76%. The sky was obviously very bright, with the near full moon. This was reflected in an SQM value of only 16.9 mag/arcsec2.
Capturing
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Takahashi Mewlon-180c + 0.8x reducer, Esatto 2”
RainbowAstro RST-135E, Berlebach Planet
QHY268c, cooled to -15 ºC
Astronomic L3 luminance filter, 2” mounted
Askar FMA180 guidescope, ZWO ASI290MM
Fitlet2 (Linux 20.04), Pegasus Powerbox Advance
KStars/Ekos 3.5.6, INDI Library 1.9.3, PixInsight 1.8.9, PlanetarySystemStacker 0.9.1, PTGui Pro 12.11
This image was taken on the very first night out with the Mewlon-180c telescope. It was not intended to do any serious imaging. The goal was to get familiar with the system, guiding, focusing, etc. Out of curiosity the system was pointed at the moon, and video-streams were recorded. At a later stage, the system was used to make images of M3 (considered official ‘first light’) and M13.
The setup with the Mewlon-180c and RST-135E mount is relatively lightweight and can easily be transported. With this experience of the moon, more moon and planetary work would suit this setup well.
The newly acquired Takahashi Mewlon-180c, setup with QHY-268c camera on the RainbowAstro RST-135E mount.
Image
The Field of View of the Mewlon-180c, even with 0.8x reducer/flattener, was not sufficient to capture the full disk of the Moon. Therefore two images were shot that were later stitched together. The images were recorded as video-files in the SER format. One file contained 263 frames, the other 344 frames. Ekos was used as the acquisition software. Gain and exposure settings were not recorded, but the histogram was maximised to about two-thirds of maximum. The full 26 megapixel readout of the QHY268c camera was used, which maxed out to about 6 fps.
After stitching the two images together, the final image has a resolution of 5777 x 5777 pixels, or 33 Megapixels.
Processing
No calibration was applied to the images. The video-files were processed using Planetary System Stacker (PSS). This is relatively new software and supports both stacking of the individual frames and wavelet-based sharpening of the stacked images. In that sense it combines functionality from the popular alternatives Autostakkert! and Registax, with an exceptionally good quality of the final output. PSS is open source and multi-platform. Installation on the Mac was a very simple procedure.
PlanetarySystemStacker is a new, multi-platform tool for stacking and processing moon, planetary and solar images.
The two videos contained 263 and 344 frames. The 20% best frames from each video were stacked, so 53 and 69 respectively. Most default settings in PSS were untouched when it came to selecting the alignment points, defining box sizes, overlap, etc. The amount of warping of individual alignment points is indicative of seeing conditions during the imaging. PSS shows a frequency distribution of these warping distances. The maximum warping was only 2 pixels, which was very good.
Placing of Alignment Points (left) was done using default settings. Each individual Alignment point was only warped by a very small amount as the frequency graph shows (right).
The stacked image was sharpened using three wavelet layers, each with increasing radius and decreasing amounts. RGB alignment was applied using the automatic function and resulted in small shifts of maximally 1 pixel in the Red and Blue channels. The stacked and sharpened PSS images were saved as FITS files and further processed in PixInsight.
First the colour was calibrated, eliminating a strong green-cast on the whole image. Next CurvesTransformation was used to give the images a boost in brightness, contrast and saturation. Finally both images were further sharpened with a mild UnsharpMask process (StdDev 1.6, Amount 0.4) and exported as TIF-images.
The two images were stitched using PTGui Pro. This is probably overkill, but since it is a familiar tool, it was chosen over a Photoshop merge. One of the benefits of PTGui Pro is that the aligning process is very precise with many control points automatically placed and that the seem is very well blended between images. The stitched image was exported as a psb file, which was rotated in Photoshop to ensure that north was north and south was south.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
