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Jupiter July 4, 2021

2021 July 6

09:37:37 UT


10:01:37 UT

Jupiter was well placed in the pre-dawn morning sky of July 4th.  It was nearly due south, approaching the celestial meridian, and 42° above the horizon.  

I got the C8 rig powered up and Jupiter focused on the imaging chip around 04:30 a.m. (09:30 UT). It was still dark. The sky was clear.

I started capturing video right away and kept going until around 05:05 when I noticed it was becoming more difficult to keep the image histogram level at 60%-70%. I kept increasing exposure lengths and gain levels, but Jupiter’s image kept getting fainter. Finally, I looked up at the sky. Clouds!

It was now overcast from horizon to horizon. Jupiter, usually very bright and visible to the unaided eye, was only faintly visible as a pale dot through the clouds.  The imaging session only lasted a little over a half an hour.

At the start of the brief session, the Great Red Spot was not visible, having just rotated out of view on Jupiter’s preceding limb. And, The feature known as Oval BA had not yet rotated into view on Jupiter’s following limb. As usual, my timing was not good. I managed to miss both.

So, what we’re looking at here are Jupiter’s belts and zones. While there are no big dramatic features to see, the seeing was good enough for my small rig to resolve some detail in the belts, and to resolve two small white ovals in the south polar region. These two ovals are the leading end of a string of ovals that precede the much larger Oval BA, which I should have captured if he clouds hadn’t intervened.

Good seeing is relative though. On the imaging scale devised by world-renowned planetary imager Damian Peach, the seeing only rated a “fair” grade.  According to the Peach scale, fair seeing  shows: “Significant fuzziness or undulation. Fair contrast. Larger scale detail well seen. Minor details mostly invisible.”

As this short video snippet shows, the seeing during this session falls squarely into Peach’s “fair”

This video snippet, captured on July 4, 2021, shows a fuzzy, quivering image of the giant planet Jupiter. The atmospheric seeing conditions would probably be rated as fair on Damian Peach’s seeing scale. Contrast is good. Large scale features are visible. Some smaller scale features are occasionally seen, but mostly not.

category. By Oklahoma standards though, the seeing rarely rises even to this level. Compared to the usual blurry soup the sky serves up here, this session’s seeing might be rated “good.” Oklahoma’s flat midcontinent location, with its near-constant surface winds and turbulent jetstream overhead, puts us under a roiling ocean of air that causes the planets to shimmy and dance when they should be holding still for the camera. As a result, here in Oklahoma, when Jupiter holds still enough  to show good contrast and some large scale detail, fair seeing is really good seeing.


Date: July 4, 2021
Telescope: Celestron C8 (203mm F10) and Orion Shorty 2x Barlow
Camera: ZWO ASI224MC
Captured in FireCapture. Aligned and stacked in AutoStakkert. Wavelets and color balance in Registax. Color levels, unsharp mask, crop, in GIMP.

[1] 09:37:37 UT    800/3703 frames, 53 fps,  15.7 ms.
[2] 09:50:34 UT   2000/3824 frames, 55 fps, 14.26 ms.
[3] 10:01:37 UT   2000/6663 frames, 69 fps, 14.26 ms.

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