han59

You can retrieve DSS1, DSS2 images online using RA,DEC coordinates and scale. I'm not aware if you can retrieve directly them based on name. ESO also allows to retrieve the images as GIF of JEPG Here some hints:

Below a Hyperleda (PGC) annotation of the image using ASTAP. Just download the Hyperleda database installer from the ASTAP webpage : Han

An RA of 202.367 is in degrees [0..360] while 13.491 is in hours [0..24] They are the same since 202.367*24/360=13.491

Interesting test, but since imaging takes hours, the best bang for bug is some patience. Normally a huge amount of mbytes are processed. I'm surpriced HDD vs SSD doesn't makes a real difference.

You could also have a look to VM Ware player. Virtual box or VM Player both will work well. I use VM player to run Linux in my observatory under Win7 for testing and can control the mount and cameras. I use also VM player to run WinXP for an old scanner and several Linux flavors under Win10. Running a Mac worked for me under Virtual box. The nice thing is that you can keep several virtual machines and copy/modify them as you like. Just try and see how good Virtual box or VM Ware player works for you. What's important is that you get the copy & paste working between the virtual machine and the host system. You can copy also astronomical files to a disk and unmount it again so it becomes accessible to the host system but that's more cumbersone. You can also have a shared directory, but I never managed to get that running in either Virtual box or VM player. An other problem can be the resolution. Some Linux distributions have problems to display the full resolution in the virtual machine. The host machine will require 4 gbyte minimum but 8 gbyte will works much better. The speed is slower but still reasonable good. Stability is good. I assume you want run Linux under Win10. I would suggest to use Lubuntu since it uses less resources then Ubuntu and the interface is more similar as Windows. Han

Thanks for the solution. I was already a little puzzled. Abell1809 is missing from my database. Now it is clear.

While processing some old image series, I had a serie of a few galaxies. Nothing special. Exposure 9x200 seconds with a 100 mm APO F/5.8 and an ASI1600 camera. But then I noticed a large amount of unsharp stars near NGC5365. Further investigation indicated they where all galaxies. The cluster has as a far I know no name. Han A small part of above image around NGC5365. De unsharp stars are galaxies. Annotated and the cluster marked with a rec circle.

Still I wouldn't recommend X-trans sensor cameras for astronomy. Getting a good star colour with X-trans pattern is more difficult unless your image is oversampled. A star has to illuminate 3x3 pixels equally for a good colour rather then 2x2 pixels. Secondly the important red is 2/9 of the pixels compared with 1/4 for a Bayer matrix. Han

Use method "Sigma clip average" for stacking. This will detect that the hot pixels are outliers and remove them.

Without an image an advice is difficult. Comets are faint and the image will be noisy. To get a good image you will need at least 30 minutes exposure time for a short focal length (500 mm) telescope and long focal length a few times longer exposure. If your sky is not very dark it becomes even more difficult to image and comet. Han

ASTAP has a new feature to align and stack images of asteroids. The alignment is called "Emphemeris alignment" and allows to align the images using the calculated position. As a test, I made in April 57 images of M95 & M96 using 200 seconds exposure. So total a little more than three hours exposure time. M95 & M96 are fairly close to the ecliptic making the images both useful for a galaxy image as for the asteroids. The images where made with my 100mm F/5.8 APO and an ASI1600 MMC camera. The SQM value in my garden reaches about 20.4 maximum. First I made a normal stack and annotated asteroids in the image. The number of asteroids in the ASTAP annotation database was set at 200,000 and the limiting magnitude at 20. Quite a few asteroids are annotated. However, they are not visible due to the self-movement. ASTAP has the ability to align and stack the images based on the calculated position. The program will show in a drop down menu the asteroids within the range of the image. Then it is just a matter of selecting one of the asteroids and then to re-stack the image. Eventually I can see that the limiting magnitude for my 100mm telescope (after 3 hours exposure) is about magnitude 19.5. See selection below. Han Asteroid 5741 with magnitude 17.9 8383 with magnitude 18.4 25232 with magnitude 18.9 and 25799 with magnitude 18.8 Asteroid 12601 with magnitude 19.4 barely visible:

They have had plenty of clear skies moments to test there first assembly. Makes you wonder.

I have made 5 minute video demonstrating how to measure the magnitude of comet C/2019 Y4 (Atlas). It's an almost fully automated process. The comet flux is measured and converted to a magnitude using the imaged stars as reference. Calculating the star magnitude/flux relation is fully automatic using Gaia DR2 catalogue as reference (calculated Johnson-V). The only manual operation is selecting the area and removing the stars near the comet. Video: https://youtu.be/BEjcSm_cZx8 Feedback about this new method is appreciated Han

You better solve the tilt in X (between left and right). That reduces the quality. Most likely the stars are on one side a little larger. Assuming the average FWHM is about 10, the difference is 2.9/10 is 29% Sometimes just remove and replace the camera could help. Or turn it 180 degrees and look to the difference. Han

You probably are better off by stretching in APP or ASTAP. In GIMP you could stretch using curves, but most likely like in Photoshop you will loose colour of the faint objects: See e.g.: http://allthesky.com/articles/colorpreserve.html or here https://www.markshelley.co.uk/Astronomy/Processing/Colour_Preserving_Stretch/colour_preserving_stretch.html And explained in this little graph: Input: blue=5 red=10 The input colour ratio is then 10/2 is 2. The curve gives these values after stretching: Output: blue=0.26 red= 0.38 De output colour ratio is then 0.38/0.26, about 1.5. De result is less colorful. A better method is colour preserved stretching as implemented in ASTAP: in de range of 0..1: luminance:=(red+green+blue)/3 luminance_stretched:=gamma_curve(luminance) red_output :=luminance_stretched * red greenn_output:=luminance_stretched * green blue_output:=luminance_stretched * blue The ratio between red, green and blue so the colour stays the same. Only the luminance is stretched. Han