Sunday, March 18, 2012

Project for a cloudy day

Plot of the regions of sky where my imaging system cannot go without a pier flip.
I sometimes find that my scope can't point at the planned target due to a conflict between the camera and the tripod. The solution is to do a 'pier flip' - i.e. to rotate in RA by 180 degrees. However, after a some time tracking I'll need to flip back because now the camera-tripod conflict arises anew. I'd like to try and map out the regions of sky which are problematic so that I can take them into account when planning. Hence, during this cloudy day I set up in the living room and started mapping out what my limitations are. First, I set the scope on the west side of the mount when pointing at the meridian (I call this my 'normal' configuration), put the RA setting circle at 18hrs. Next, I put the dec. at 0,10,20,30..90 deg and for each value noted down at what (if any) RA value there was a camera-tripod conflict. I then did the same thing with the scope on the east side of the mount (I call this my 'pier flip' configuration). Using a planetarium program (time set to June 24 at midnight  for which RA=18hrs passes the meridian) I then translated my RA, dec. limitation values into az, alt. values. The result is shown in the figure where zenith is in the middle and the horizon runs around the circumference with azimuth angles indicated. For each configuration I have a region where I can't point, shown in red and blue. Now, if only I could figure out a way to use this information in an easy manner to predict if and when pier flips will be required for a given object on a given date. Does anyone know of a good way to do this?

Saturday, March 10, 2012

Bubble in Hubble

Bubble nebula using the Hubble palette. Total exposure time is 33 hours.
Finally - I have managed to create an image which is somewhat of a finished product! Sometimes I nearly despair, feeling that I never reach this stage. Instead I fiddle around with calibration, stacking and analysis for weeks and weeks until I start diffusing into other projects, leaving much 'unfinished' work behind me. This morning I got the 'final' stacked, narrowband images of NGC7635 - the Bubble nebula - wrapped up and I vowed to attempt to make something pretty out of it by the end of the day. I chose to use the Hubble palette where SII, H-alpha, OIII are assigned to R,G,B respectively. I also have short exposure length RGB data, but have not yet processed this into something that could be used to create more natural looking stars.

The seeing in this image is ~3.2". It would have been nice to have 2" instead! I have not fallen for the temptation of sharpening and I don't think it would help much.

Earlier today I sent the narrowband images to my good friend, Henrik Bondo, who will attempt to process them into something that has more natural looking colors. So, for many reasons the image shown here is not the final one, after all. We can keep on working on our projects forever - and that's OK!

Full resolution JPG: click here
Some processing details: click here

Saturday, March 3, 2012

High thin clouds on and off

Had the AT8RC setup out again last night. Prospects were not very good due to forecasted high, thin clouds and haze. In addition there was a 60% full moon in the sky. Before midnight I did IC417 in OIII light. Inspecting the calibrated images showed that the nebulosity was completely washed out. Sky flux this time was 60% higher than last time I shot IC417 in a moonless and less hazy sky.

After midnight the target was M100 in green light - haze seemed to be less severe then. Comparing to red light data from a few weeks ago with no moon and less haze suggested the images to be of reasonable quality, but not as good. The background ADU was around 2000, compared to ~1000 earlier. I'll do a critical comparison with future M100 green images to find out if last nights run is useful at all - I am not too optimistic!