Cassiopeia Observatory

M56 Globular Cluster; Jupiter Europa Transit
Posted: 26 November 2011

After a period of cloudy skies, the weather finally improved and I opened the observatory Friday, 25 November 2011, at 1813 MST, 53°F. Before I opened the dome it was necessary to wipe off some water from the early morning rain. At 1820 MST, viewed Venus at 77X, low in the west and in some tree branches. Then Jupiter at 77X. Four moons were visible. Europa would begin transiting the planet's disk at 1946 MST, followed by its shadow at 2108 MST. At 1837 MST, I switched to the 9.7mm eyepiece (206X) + moon filter. Seeing was not very good. I looked up at the sky and there was a "Swan Nebula" shaped cloud passing Jupiter. No wonder the seeing wasn't good!

1845 MST: viewed two DSOs in Lyra at 77X: M57 (Ring Nebula) and M56 (globular cluster). I decided to image M56 with the D7000 DSLR at prime focus. I did a focus test on Vega with the Bahtinov Mask. Seeing was still not very good. I checked the humidity and it was currently 65%. That's why things felt damp! I took 15, 30, and 60 seconds, ISO 6400, unguided exposures. This is the 30 second exposure, slightly cropped:

At 1911 MST, I ended imaging and returned to Jupiter. Seeing was a little better now. I began watching Europa approach the planet at 206X with a moon filter. I turned on the shortwave radio and began monitoring the WWV time signals. As first contact got closer, the seeing got worse, making it difficult to see the gap between the moon and planet's limb. First contact appeared to occur at 1944 MST. Europa appeared as a small bright disk on Jupiter's disk a few seconds after 1946 MST. Second contact seemed to occur at 1949 MST. At 1951 MST, Europa was a bright "star" on Jupiter's disk, just south of the SEB.

I began setting up for iPhone 4 afocal imaging of Jupiter using the MX-1 adapter. I used the FiLMiC Pro video recording app. This app allows both the focus and the exposure to be locked. Given the poor seeing at times, I was hoping that the app would provide a good video recording for stacking. Unfortunately, due to the poor seeing, Jupiter moved around too much for good stacking registration but I was able to stack 2904 frames from a two minute video recording, afocal 9mm eyepiece + moon filter + 2X Barlow Lens. This is the (cropped) result:

Unfortunately, seeing was not good enough to capture Europa in front of Jupiter. But FiLMiC Pro did a good job of maintaining focus and exposure during the recording. FiLMiC Pro also allows setting of resolution. I intially recorded at 1280x720 and the image above was taken from a recording at that resolution. I tried recording at 480x360 but Jupiter was too overexposed to be usable.

2020 MST: ended iPhone imaging and returned to observing Jupiter and Europa. With the moon filter, Jupiter's brightness made seeing Europa nearly impossible. But with the moon filter, Europa was fairly easy to detect. 2108 MST: Europa's shadow now visible at limb. 2137 MST: Europa was difficult to see against the bright clouds but was still visible, just south of the SEB. Shadow was easily seen.

I began setting up for D7000 DSLR imaging of Jupiter at prime focus + 3X TeleXtender. I did video recordings at 1/320sec, 1/250sec, and 1/200sec shutter speeds at ISO 800. The preview on the D7000 screen looked good but unfortunately, these were all underexposed and not usable for stacking. I will up the ISO to 1600 for my next attempt.

Due to the high humidity I decided to end the session early. The forecast for the next night was for clear sky with much lower humidity. I have rescheduled the planned observing and imaging targets to the next night.