Christmas seems to be coming early in 2020 amid the Covid-19 pandemic as many people have been putting up their Christmas decorations early in November. We haven’t put our Christmas decorations up yet but I nevertheless felt justified in observing NGC 2264, also known as the Christmas Tree Cluster.
This photograph includes four different astronomical objects:
- The Christmas Tree Cluster, an open cluster of stars embedded in a glowing red star-forming cloud. The rotated horizontal Christmas Tree is to the left of the cone; the very bright star in the centre is the tree trunk; the bright star just to the left of the cone is the tree topper; and probably now you can make out the triangular formation of stars making a Christmas tree shape.
- The Cone Nebula (on the right), a dark cold cloud of dust and hydrogen backlit against a glowing hydrogen emission nebula.
- The Fox Fur Nebula, the bright white region to above right of the very bright central star.
- The Snowflake Cluster, just to the left of the Cone Nebula.
For some reason, occasionally there are nights when little works on a technology front. This was one of those nights. I set up with plenty of time to spare as NGC 2264 is not observable from my back garden at this time of year until about 10pm. I used the early evening time to acclimatise the OTA and take dark frames. The trouble began once I tried to start imaging: I installed my quad-band filter and just after I’d finished orienting the sensor and focusing, the sensor misted up with condensation and I couldn’t see anything (I don’t understand the physics of how adding a warm filter to a cold OTA resulted in condensation, but it happened)! I eventually removed the filter altogether to acclimatise it more quickly, I then I had to refocus and reorient it again.
Once I’d framed my target, I then had to contend with terrible guiding accuracy. Usually I can easily guide at 0.6″ root mean square (RMS) error, which is more than perfect for my setup. For reasons I still do not understand, however, on this night I was guiding at between 1.2″ and 2″ RMS error, which is awful and gives star streaks. I recalibrated PhD2 near the celestial equator, I recalibrated PhD2 near the target, I checked the balance of the OTA, I redid the polar alignment, I checked the clutches were engaged, I checked the mount wasn’t sinking on the wet grass, I switched it all off and started again, I tweaked the PhD2 control gains, and I experimented with different guiding exposures. After all that, the best I could manage was between 1.2″ and 1.3″ RMS error. 1.2″ is the maximum I can tolerate for sub-pixel guiding, and so it was passable, and I accepted it in the interest of actually getting some data.
Imaging finally commenced at about 11pm and came to an end at about 2am as it clouded over. I captured 34× 5-min frames, and amazingly, 32 of them were acceptable for the final integration. I was really pleased to get this image despite the relatively short integration time, the 85%-illuminated moon, and all the technical hitches I experienced. It was worth persevering for!
- 32× 300-s light frames (Gain 900)
- Full use of calibration frames (darks, flats and dark flats)
- Explore Scientific ED 102 mm Apo f/7 refractor
- Sky-Watcher EQ6-R PRO SynScan GOTO equatorial mount
- Altair Hypercam 294C PRO colour fan-cooled camera
- Altair quad-band one-shot colour (OSC) 2″ filter
- Revelation Adjustable Field Flattener
- Altair 60mm guide scope
- Altair GPCAM2 AR0130 mono guide camera
- Topaz Labs DeNoise AI