Imaging on a Cool Night

Clear nights have been rare this fall in the Vancouver area. In October, we set a record for rain on 28 out of 31 days while normally there are about 15 days of rain. November was not better with 25 rain days – the 4th most rain days for November. But I took advantage of a recent clear night last Wednesday (Dec 7th) to get in some imaging of the Moon and the Pleiades.

Moon Image
The Moon taken with a Nikon D5100 and Skywatcher Esprit 80mm refactor.

The cool weather presented some challenges. At -3°C, the temperature was slightly below freezing but quite manageable for me with a good jacket, boots, and gloves.

My equipment didn’t fare as a well.

The first problem became apparent when I went to polar align my mount. I built a concrete pier topped with an aluminium adapter last summer but had removed the CGEM mount head during the two months of rain. So I reattached the mount head and stuck my 80mm Esprit refractor on it early to allow it to cool down. A couple of hours later, I went to polar align the mount and found that I could not adjust the azimuth at all: a thin layer of frost and snow on the adapter likely froze the mount head to the adapter and prevented it from moving. Poor polar alignment meant that I would have to use short exposures for imaging – not a problem with the moon at all and I could try stacking lots of short exposures for the Pleiades (lucky imaging).

I powered up the CGEM mount (it is a goto mount) and looked at the LCD hand controller to work through the initialization procedure. The second line of display on the hand controller appeared garbled and unreadable – apparently, LCDs are sensitive to temperature as the fluid tends to “stiffen” in the cold. I managed to get through the initialization and start tracking mostly by pressing “enter” to accept the defaults but decided to manually slew the mount rather than trying to do a star alignment and using the goto capabilities.

Finding the moon was easy, and I managed to take a few images though the camera battery only lasted about ½ an hour in the cold. Fortunately, I had a spare battery charged and ready to go for the Pleiades.

Finding the Pleiades was more difficult. The Pleiades are an easy naked eye object even under normal city light pollution. But my yard in Coquitlam was still covered with 10-15 cm snow from the previous day. It was amazing how much light reflected off the blanket of snow and made it difficult to spot the Pleiades. I did manage to find them after a few minutes of random hunting – thank goodness the 80mm Esprit has a wide field of view!

I ended up getting 45×15 second sub-exposures of the Pleiades but, as a final insult, part way through my imaging, the neighbours decided that the cool night was a good time to use their outdoor hot tub and turned on a bunch of bright exterior lights that shine into my yard. Ah well, I still stacked and processed the  sub-exposures to get an image that shows some of the nebulosity around the Pleiades.

Pleiades Image
Pleiades with some nebulosity. The image is a stack of 45 x 15 second sub-exposures.