Cassiopeia Observatory

Comet C/2012 S1 ISON (Mag +16)

Posted: 4 January 2013

The observatory was opened Thursday, 3 January, at 1812 MST, 46°F, to clear skies but with a strong breeze blowing. The main goal for this night was to capture confirming images of Comet C/2012 S1 ISON, currently about Magnitude +16 in the constellation of Gemini. For more info on Comet ISON and other current comets, see Curt Renz's Comets Page. After opening the observatory, I began playing "Music from Cosmos" (Carl Sagan's TV show) on the iPOD in the SkyShed POD. Perfect background music for a night of astronomy.

At 1825 MST, viewed Jupiter, 77X. Tonight was another interesting view showing "5" moons. One of the "moons" was actually a star. Seeing was not good again this night, and the strong breeze did not help. I took a prime focus image of Jupiter and its moons with the D7000 DSLR and 8" LX200-ACF, "hat trick", ISO 200. This is the cropped image, showing the 5th "moon" below Ganymede, along with the moon's identified in Pocket Universe (iOS app):

At 1850 MST, viewed M1 (the Crab Nebula), 77X. As I was observing it in the eyepiece, a satellite passed through the field-of-view (FOV) This was the fourth satellite I had seen in about 30 minutes. The first one was a naked eye satellite passing near Jupiter. The second one was seen in the eyepiece while observing Jupiter a few minutes after the first one. The third was another naked eye satellite passing through the Hyades cluster (Taurus). At 1858 MST, I returned to Jupiter to watch the "dance of the moons", 77X.

At 1914 MST, I began preparing to take prime focus + Off-Axis Guider images of Comet C/2012 S1 ISON. At 1943 MST, I did a focus test on the star Pollux using the Bahtinov Mask. I then did a 10 minute, guided, ISO 6400, exposure of the same location I had imaged on the previous night to see if I had actually properly identified the comet on that image. As it turned out, the faint fuzzy object I thought might be the comet in that image was in the same place on this night's image. Hence, it was not the comet.

I then slewed to the RA/Dec of the comet (as shown by SkySafari Pro on the iPhone). I had to slew around quite a bit to locate a good guidestar, hoping that the comet would still be in the camera FOV. I did the first guided 10 minute exposure, ISO 6400, beginning at 2016 MST, and the second guided 10 minute exposure beginning at 2116 MST. In between the two exposures, I closed the observatory dome due to the strong wind and low temperature (38°F). I completed imaging at 2126 MST. The wind was still blowing, so I began closing up for the night.

In post-processing, once I imported the two images of the comet into Aperture, I toggled between the two images ("blinking") and could easily see that Comet C/2012 S1 ISON had been captured. This image, from 2116 MST, shows the comet arrowed and in the magnified inset:

This next image (an animated GIF) easily shows the movement of the comet in one hour:

I will take more images of Comet C/2012 S1 ISON next month to show any changes. It should be a little brighter then. I plan to continue imaging the comet monthly as it approaches its best viewing later this year.

Comments are welcome; use the Comments section below, or you can Email Me. Thanks.