Mars/Neptune Conjunction, and Moon/Comet 45P Conjunction

Dec 31, 2016

A nice way to end the year. Mars passed Neptune only 2' away after both set, but still 6' away while it was best visible for us in the early evening. And just after twilight, the 7% cresent moon passed just 3 degrees north of Comet 45P which was at magnitude 7.0 or so. Jay and Benno and I wanted to photograph both events, of course! But also, our successful re-boot of the Gemin 1 system at Cabrillo Observatory's dome scope the previous night meant it was time to re-build a mount model. This would take several hours, and my personal plan was to stay after the photographing and spend the night at the observatory, then driving in the early morning to meet Rick Ferrell and we'd head to Carmel for the annual Rio Resolution 5K/10K races.

The Moon / Comet 45P Conjunction

We set up the GM8 mount, polar aligned, and put on the home-made mount board with camera attachments. I tried to get familiar with our new Canon Rebel T1 camera but in the time crunch, it was just way too different than the familiar Nikon, so I pulled it off and remounted with the Nikon D7000. Benno shot with his Canon. Kirk did shooting with his tripod mounted camera. Once it was late in twilight, the comet was clearly visible in Benno's photos as a green fuzz below and left of the moon. Encouraged, I looked at my 6 sec shot, not wanting to blow out the moon, and saw the comet and perhaps even a bit of tail or so I thought. We each took many shots intending to stack later. It stayed above the redwood trees on the ridge long enough to get off a good half hour of shooting. Now, after processing, I don't see a tail at all in the normal direction away from the sun, but I do see a hint of a faint greenish gas tail in the solar direction. But, that makes little sense. A dust tail could be in that direction, but not likely the fast moving ion tail. Maybe there's just no tail at all?

Kirk's comet shot. Sigma SD1 camera, 8 seconds, f 4.5, iso 1600, focal length 135mm (202mm 35mm equiv).

A stack in Registax 5 of 29 images, 6 sec each, f/5 with 200mm zoom on Nikon D7000 at ISO 800, guided on GM8 mount. Moon trailed as did redwood trees a 1/4 mile away on ridge. Comet 45P is the green slightly fuzzy object at about 8:30 o'clock from the moon and just above the blurry trees, near a brighter star to its lower left.

It was saved as .png in Registax because it didn't have enough memory to save it as a TIFF. Could open .png (46 Meg file) in PS CS2 but couldn't do anything because of 'out of memory', so 'saved for web' and closed out PS and re-opened, then could work on it a bit more. Saturated green more, large brightening in curves. I probably could have done deeper images than 6 seconds since clearly the moon wasn't going to feature well.

Same image, but comet flagged, for sending to

The moon and a blue B-type 6.2 magnitude star


Mars and Neptune


This is a 300 second (5 minute) auto-guided shot with the ST2000xcm camera on the 12" f/6.3 LX200 reflector in the dome. DDP color process better preserves the bright regions, and at this exposure both Neptune and Mars are saturated. The goal of this shot was to get faint Triton to come up well, and also to get the two 16th magnitude Palomar catalog galaxies immediately to the right of bluish Neptune. Stars to 17th or even 18th magnitude are recorded here, even though the altitude now is only 24 degrees in the southwest. The big bright donut is a secondary reflection of Mars, far out of focus. An inherent "feature" of any corrector-plate (e.g. SCT) scopes.

Kirk B sent this nice image from some software he has, showing the moons of Mars and Neptune and the two faint galaxies. The thumbnail shows the orientation his software downloaded, but the fullsize is tipped to agree with the camera picture at left.