Astrophotography by Torsten Mueller

The Arp Project

Click here for all Arp related images

I can´t remember the exact reason, but when observing the first galaxies more in detail, i was looking for some more scentific project approach. I´m not the pretty picture photographer, every integration more than several hours is just too long for me and the short nights under the week. Then i stumbled across Halton C. Arps work about the morphological classification of galaxies (1966). His work resulted in a catalog of galaxies, sorted by specific classifications. He used the Palomar Telescope to get images, that means, the catalog is limited to mostly northern sky objects down to magnitude 17. In sum, the catalog contains 338 objects, all within the reach (more or less) of my telescope (regaring brightness and size) So, i decided to try to follow Halton Arps footsteps and photograph each object by myself!

Here is some shortend goals of the project:

In preparation, i aquired some detailed information about the objects. I created some python scripts to calculate the best visibility of each object over the next years.
That means, the object should be more than 10° over the horizon, or more than 30° if its in the eastern sky. Additionally, it should be more than 90 degree away from the moon.
I quickly noticed, that more than 80 objects will never get hight enough to be see at the given location. This was quite disappointing because then i have to take these photos somewere else. I will come back to this point later.
Most galaxies are visible in winter, when the centre of the milky way is not in the sky. That means the best observation time ranges from december to april. (Remark: In a moonless late january night, all Arps become visible at proper locations!) Taken the disturbing moonlight each month and the weather in germany into account, the usable nights are quite few. Each object needs at least 20 minutes integration time, better about 1 hour to get proper signal. That means, it takes long time for me to do all the images. The project will take at least 3 years, probably 4 years.

Overall integration time for the Arp project: 107.61h
Arp catalog for Cartes du Ciel

In preparation, i collected all the data of the Arp objects. None of the online sources provided all needed information. So, i had to collect the data by myself with the use of Simbad, Aladin, and the NED. Then i preparated a catalog for Cartes Du Ciel with the objects.
There are two little drawbacks:
1. Only the Arp object itself is in the catalog, not the parts (especially for groups,chains and clusters this may be errorneous), For these combined objects, a mean size and the brightest magnitude is used
2. The Prefix "ARP" is missing. So if you want to search for an Arp you just enter the number itself in the search field. i.e. "188" and not "Arp 188"

The second (extended) revision of this CdC catalog is in work, but this may take some time to complete (Rev. 1 needed about one -fulltime- week to collect...)
- Unzip to a location on your PC (i.e. in the CartesDuCiel/cat/ folder)
- select Catalog from the Menu, choose the proper tab for own catalogs
- located the arpcat index file.
- Enable the catalog
- Close the dialog -> search for any object with the search field.

Feel free to use it for yourself and in a non commercial way. If you found errors or just want to share "your" Arp project, feel free to drop me an Email (, i'm looking forward to read about.

Recap after 1 year
As of January 2020, exactly one year went by. I was able to shoot 48 Arp objects (in a way that i can show them, of course, there were some more but due to technical or other reasons, i could not process them). So, 14 percent are done... That means, it will take much longer than estimated. But its real fun doing, so i'll keep pushing :)