by Albert Highe
| Wednesday | min temperature 33ºF; clear skies. |
|---|---|
| Thursday | min temperature 39ºF; clear initially, but after midnight thin clouds moved in from the north, first obscuring the horizons, then moving upward. |
| Friday | min temperature 41ºF; clear skies, excellent seeing after 1AM. |
| Saturday | min temperature 46ºF, again clear skies with excellent seeing after 1AM. |
I took and set up both my 12.5" f/5 and 17.5" f/4.5 ultralight scopes.
My intention was to observe as many galaxies in the Perseus Cluster, Abell 426, as possible. To be more precise, my goal was to observe at least 100 galaxies.
The Perseus Cluster has special meaning to me after I "discovered" it on my birthday at CalStar two years ago. While searching for NGC 1275, I was surprised to see nine galaxies in a relatively narrow field with my 12.5" scope. Four of the brighter galaxies, including NGC 1275, the brightest, lie at the corners of a parallelogram. I could see quite a few more while scanning the immediate area. I've since spent a lot of time on my "Birthday Cluster", returning to it again and again to enjoy the views and to seek out new members. However, three questions arose. Do all the galaxies I see in the area belong to the cluster? Are there other cluster members not plotted in Uranometria that I can see? Are there cluster members outside the 3º-diameter dashed circle shown in Uranometria? One can ask similar questions about the number of galaxies plotted in "The Sky" or other programs.
In preparation for CalStar, I spent the past several weeks searching the academic literature for information on the Perseus Cluster. Cluster members have been studied extensively and quite a lot is known about their radial velocities, magnitudes, and morphologies. From a variety of sources, I compiled a list of approximately 800 galaxies belonging to the Perseus Cluster! Most of these galaxies are too faint for most amateurs. Galaxies within a square approximately 3º on a side (10 square degrees) have been identified down to approximately mag 22. Galaxies out to a radius of approximately 3º (6º-diameter circle) have been identified to approximately mag 15.7.
I sorted the list by photographic brightness and created a target list of approximately 170 galaxies down to almost mag 16. I had planned to view as many members as possible with both 12.5" and the 17.5" scopes. Jamie D. warned me that it was too ambitious. Although I focused on this goal for four nights, Jamie was right.
One limitation is that I only had approximately 2-1/2 hours to observe the cluster each night with my 17.5". I had to wait to almost 10PM before Perseus rose high enough to allow viewing of faint galaxies. After approximately 12:30AM, the eyepiece height was too high to continue with the 17.5". I had planned to begin using my 12.5" at that time. But after 2-1/2 hours of intense study on ultra-faint fuzzies, I was tired. Instead, I spent my time socializing and viewing bright favorites. Before 10PM, I looked at bright favorites and hunted down other faint fuzzies in Andromeda and Triangulum.
Preparation was very important. Only the top 35 or so galaxies are brighter than mag 15. I created a database of my target galaxies and added it to "The Sky". This is a useful tool to see the entire set and to plan a night's observing strategy. "The Sky", or even Uranometria, is generally sufficient to find the brightest 35 - 50 galaxies. For most galaxies, I downloaded and printed finder charts from the Digitized Sky Survey. The photographic images were essential to locating the precise position of each galaxy. Only after concentrating on a particular location did most galaxies, "pop" into view with averted vision.
So, how did I do? I hit my mark of 100 galaxies (out of 102 that I attempted to track down). I still have over 60 targets to shoot for. At this rate, it is likely that I could see as many as 150 galaxies in the Perseus Cluster with my 17.5" scope. I suspect even more are possible in very transparent skies. During the next few months, I also plan to repeat the survey with my 12.5" scope.
CalStar 2002 was a success and a lot of fun! Thanks to all who planned and organized it.