STARGAZING SESSION IN CALIRAYA , LAGUNA
April 9-10, 2005
by Jett Aguilar
Our April Caliraya trip was really a resounding success and might be the best session for the year both in the number of participants and of objects viewed and imaged. We arrived at the Caliraya Hilltop resort welcomed by a fantastic mountain view of a beautiful summer sunset. After a short but hearty (high cholesterol ;-)) dinner, the group didn't waste time setting up their equipment at the bridge. I was looking forward to seeing Mon's new "big gun" setup the colossal Atlas mount carrying his 10 inch Newtonian. His setup was really impressive and I couldn't help looking at the huge improvised bar-bell counterweights. It seems that Mon had transported a whole mini-observatory to the resort.
Tracking seems to be working very well when I took a peek at Jupiter with its prominent equatorial bands. I'm sure Mon will be doing a lot of imaging soon! At first, we were all apprehensive about the poor sky transparency but at least there were no heavy clouds spoiling our view of the Caliraya dark sky. Polaris was much fainter this time compared to last month but James and I were still able to do our polar alignment after some effort. Later however, both James and I experienced tracking problems with our GP-DX mounts I couldn't do unguided exposures for more than 2 minutes without producing star trails. I believe that my polar alignment was a little off but I decided to proceed with my imaging anyway. I worked around this limitation by doing multiple short 2 minute exposures with the intention of doing image stacking later.
I was having a hard time choosing my first target (there were so many of them!) when Joel walked past me and I asked him what he was looking at. He answered - "the sombrero galaxy", and I then answered, "Good, then I'll image that now!" I set the coordinates for Messier 104 (in Virgo) in my Skysensor 2000 and had no problem centering the Sombrero in my LCD screen. A 2 minute exposure easily showed the galaxy with its prominent dark lane. It was during this time that I first noticed star trailing when I took image exposures longer than 2 minutes. I then went back to 2 minutes and took as many exposures as I can (10-15). I also took a 2-minute "dark frame" image with the telescope cover on. My routine was - cover the front of the scope with a black cardboard, click the shutter, expose for 2 minutes, cover the scope again and release the shutter. I view the image in my laptop which is connected to my Canon EOS 300D via a USB cable. I spent almost the entire evening and early morning squatting in front of my laptop looking at my images and I paid for my awkward position the next day when I felt that both of my thighs are stiff and sore. Unfortunately, when I looked at my images again at home, I noticed that most of the images have star trails and I was able to stack only 3 acceptable images. I did a dark frame subtraction in Photoshop before stacking the images in Maxim DL and then doing the final processing again in Photoshop (curves, brightness/contrast, noise reduction, etc.) Anyway, the final processed image of M 104 was not that bad and showed the distinctive Mexican hat shape with its prominent dark lane forming the brim of the hat .
After the Sombrero, I decided to image the fabulous Omega Centauri (NGC 5139) in Centaurus which I missed during our last session. James told me that with my 8 inch SCT I should have no trouble resolving the stars in the core on my image. The Omega Centauri is the largest and brightest known globular cluster and is really breathtaking both to view and image. Hmmm, this must be the reason why James had made the Omega Centauri a permanent fixture in the Philastro forum page ;-). I read somewhere that some astronomers are thinking that this globular cluster might be the core of a dwarf galaxy. We are indeed lucky here in the Philippines to be able to see this beautiful Southern hemisphere object.
After Omega Centauri I then attached my camera piggy-back to my SCT and took a widefield image of the smallest constellation Crux ("Southern cross") as it was disappearing thru the leaves of a palm tree in the South. Looking closely at the image I seem to discern the faint outline of the "coalsack" at the lower left corner of the cross but it might just be my imagination. Anyway, I plan to look for it again next month.
After imaging Omega Centauri, Jun Lao suggested viewing or imaging another globular cluster, M4 in Scorpius. This object would be spectacular if one could include thereddish Antares (rival of Mars) in the field of view. However despite my 6.3 focalreducer I failed to include Antares but got an acceptable image of the star cluster anyway. Tracking was again a problem and star elongation was visible in this picture. The two globular clusters make a nice comparison.
My next target was M 83, the Southern Pinwheel galaxy in Centaurus. This time my mount's tracking seemed to have improved somewhat and I was able to obtain more 2-minute images with round stars compared to my attempt on the Sombrero galaxy. I was able to stack 13 images to obtain a good image of a greenish M83 showing its spiral arms. M83 is classified as intermediate between a spiral and a barred spiral galaxy and my image was able to show this
After M83, it was past 1 AM and heavy dewing had already disabled most of the scopes in the field. Despite my dew shield, I noticed that dew had already covered my corrector plate which made further imaging with the scope impossible. James suggested positioning the scope with the front end down and wait for the water to drip out of the corrector plate. I did this but was not very hopeful that it would do the job.
At about this time I looked up in the sky and noticed that the Milky Way was prominent in the Southern horizon appearing as a long hazy cloud. I decided to take the opportunity to do wide field imaging of the Milky Way for the first time with my digital camera piggy-backed on my SCT. I again took 2-minute images with tracking and included a dark frame image at the end. I had to wipe the front of my camera lens after every shot since it gets covered with dew every 2 minutes. Visually the Milky Way looks a little boring but it was spectacular in the digital images. For the first time I was able to really appreciate looking at the "center' of our galaxy and to understand the relationships of the constellations and deep sky objects in this very rich portion of the sky. I even remembered overhearing Jun Lao talking to the group about looking near the tail of Scorpius for 2 prominent star clusters (M6, the Butterfly cluster and M7, the Ptolemy cluster) but I didn't look since I was busy imaging. However, when I reviewed my image at home, I clearly saw the two clusters just west of Scorpius' tail! Another thing I noticed when looking at my images is the lack of hydrogen-alpha (red) sensitivity of the Canon EOS 300D - with the prominent nebulosity of M 8 (Lagoon nebula) losing much of its reddish color. There are web sites describing in detail how to modify the Canon rebel to improve H-alpha sensitivity but I think that it is too much trouble and I really wouldn't want to risk damaging an expensive camera.
After imaging the Milky Way, I wiped my corrector plate with a lens cloth and tried imaging the Ring nebula in Lyra again. However, tracking was still bad and the dew came back on my corrector plate with vengeance. I had no choice but to abandon further imaging which is just as well since it was almost twilight anyway at that time.
Despite the tracking and dewing problems, I still consider the April 9-10 Caliraya trip as one of the most successful and enjoyable ALP stargazing parties that I have joined. The excellent companionship and camaraderie, the pristine dark skies, and the beautiful summer astronomical objects all combined to produce a perfect memorable session. I can't wait for the next one this May!
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