Category: Planets

This is the last batch of Jupiter images from an August session processed into a single animated GIF. Finally done. This 74-minute animation features Jupiter’s Great Red Spot with a brief appearance of moon Io. Full details of the animated image follow below.

Jupiter animation 08-15-22
This August 15th animation shows Jupiter and its prominent Great Red Spot. Jupiter’s moon Io appears briefly to the upper left as it moves out from behind Jupiter.

As noted in my previous post here, I have started adding a spacer to my Barlow lens. The rule of thumb for planetary imaging is that the f-ratio of the imaging system should be 5x the the camera’s pixel size in microns. My ZWO ASI 224MC camera has  3.75 micron pixels so the optimum f-ratio is 3.75 x 5 = 18.75. I had noticed that using a 2x Barlow lens, the resulting f-ratio with my f/10 telescope was not f/20, but slightly less at f/18. This is likely caused by the flip mirror system placed in the optical train. By adding the spacer, I increased the distance between the lens component of the Barlow and the camera sensor chip, thereby increasing the system focal length slightly and raising the f-ratio to f/22-f/23. Better to be a little bit over than a little under.

Animation Details:

August 15, 2022 09:21:24-10:34:54 UT
74-minute time-lapse
North is up
Seeing: Good
Celestron C8 (203mm SCT f/10) + Orion 2x Shorty Barlow + 12.7mm spacer (f/22)
ZWO ASI224MC with IR Cut Filter
26 image animation sequence. Each image is stack of best 3000/10000 frames.
Captured with FireCapture
Processed with AutoStakkert3!, Registax, GIMP

I’m still finishing up processing images from imaging sessions in August.  Here’s a Jupiter animation captured on August 14th. Full details below.

Jupiter & Io August 14, 2022
Jupiter on August 14, 2022. The moving dark spot is the shadow of Jupiter’s moon Io. Io is the moving orange dot. This time-lapse covers an 81-minute period.

For this session, I added a 0.5-inch (12.7 mm) spacer between the Barlow lens and the imaging sensor. This added a bit of extra focal length to the scope-camera system and raised the f-ratio from its usual f/18-19 to f/23. Adding the spacer this way effectively converted the Barlow Lens from 2x to 2.5x. Fortunately the seeing was good enough to handle the increase. The picture below shows the configuration.

The Orion Shorty 2x Barlow Lens with the 0.5 inch spacer inserted between the lens tube and lens housing. This configuration increased the distance between the camera sensor and the lens thereby raising the f-ratio of the entire telescope-camera imaging system from approximately f/18 to f/23.

 

Animation Details:

August 14, 2022 09:11:24-10:32:04 UT
81-minute time-lapse
North is up
Seeing: Fair-Good
Celestron C8 (203mm SCT f/10) + Orion 2x Shorty Barlow + 12.7mm spacer (f/23)
ZWO ASI224MC with IR Cut Filter
29 image animation sequence. Each image is stack of best 3000/10000 frames
FPS (avg) 63, 15.83 ms, gain 240, ROI 680×348, histogram 58%

I just recently got around to finishing up processing a batch of images of Pluto that I captured on August 3rd.  At the time of the imaging session, Pluto was just two weeks past opposition, with opposition having occurred on July 20th.

On August 3rd, Pluto was moving slowly against the starry background at 3.5 arcseconds per hour. Pluto’s apparent movement on that night was slow in comparison to other minor bodies in the solar system, but pretty fast in comparison to itself. For example, earlier in this month on October 2nd, Pluto was only moving at 0.5 arcseconds per hour. At this speed it would have taken two successive nights of imaging to show the same amount of movement I captured in just two hours on August 3rd.

Pluto animated GIF.
This animation shows the dwarf planet Pluto’s movement across the night sky during a two-hour period on August 3, 2022. At the time, Pluto was 33.6 astronomical units (3.12 billion miles/ 5.02 billion kilometers) from Earth. The field of view of the animation is approximately 17×12 arcminutes, cropped from a wider field of view image sequence. North is up. East is left. Image details below.

Capturing the images for this animation was a bit of a challenge. On August 3rd, Pluto’s V magnitude was predicted to be 15.0 by the Minor Planet Center and Lowell Observatory’s Ephemeris Service (NASA’s Horizons service was an outlier, predicting a somewhat brighter magnitude 14.34).

A magnitude 15 object is a pretty faint target for my 8-inch telescope, especially since I was imaging from a bright, Bortle 7, backyard, looking straight into the washed out Oklahoma City light dome to the south. In any event, I was pleasantly surprised to see that after slewing the telescope to Pluto’s coordinates, the dwarf planet popped up in the field of view, albeit faintly, right where the Lowell Observatory’s Asteroid Finder chart showed it would be. I haven’t done any photometric measurements on these images, but by my eyeball estimation, Pluto looks more like magnitude 15 than 14. 

Processing the image sequence into an animation also proved a bit of a challenge. But, ultimately, the challenge taught me a new processing technique. I normally process animations by opening the time-sequenced group of images as a set of layers in the image processing program GIMP. I then manually align the background stars in each layer with a base layer (usually the first in the time sequence) and export the entire aligned sequence as an animated GIF.  

In this case, however, for some reason, I could not manually align the layers. There was always a stubborn half a pixel difference between layers that I could not wring out. This tiny misalignment of background stars between layers caused the stars in the animation to appear to bounce around. After posting the animation on the Cloudy Nights Forum, I received some helpful comments and suggestions that led me to a solution, a solution that made the animation process easier and produced a much better alignment of the background stars.

The solution was using a program called DeepSkyStacker (DSS). I already had DSS, and had some familiarity with using it. The trick was to load the time-sequenced images into DSS and let it produce a sequence of registered (star-aligned) images, but not have it take the final step of stacking the images into a single image. Instead of having DSS create a single stacked image, I opened the registered sequence of images it produced as layers in GIMP, added some stretch and red circle highlights to each layer, and then exported the layered image as an animated GIF. The result: near rock-steady background stars with the only discernable motion being Pluto itself and the natural twinkling appearance of the background stars.

But, there’s more. DSS also calibrated each image so the background, star brightness, and color levels of each image were more uniform. I usually do this manually in GIMP, but for some reason, this was also a vexing problem with this group of images. Thanks to DSS, when I moved the sequence to GIMP, I only had to apply a simple stretch to each layer to bring the background and foreground levels to an eye-pleasing state.  And finally, there was another bonus, DSS is freeware.

This project challenged my image capture and processing skills. But, it showed that my modest 8-inch telescope and camera could capture a magnitude 15 target even under heavily light polluted conditions. And, it also taught me a faster, easier method for producing animations of the smaller members of our solar system. Thanks to this project, I’m looking forward to finding and capturing smaller and fainter objects.

Image Details:

August 3, 2022 04:31:02-06:31:13 UT
Two hour time-lapse animation.
North is up. East is left.
FOV: 16.9×12.1 arcmin   Original scale: 1.49 arcsec/pixel
Seeing: Good
12 image animation sequence. Each image is stack of 10 frames at 30 seconds, gain 200.
Captured with SharpCap
Processed with DeepSkyStacker & GIMP
Telescope: Celestron C8 (203mm SCT f/10) + Celestron 0.63 focal reducer/flattener (f/6.3)
Camera: ZWO ASI482MC
Mount: Celestron CGEM
Vmag (MPC): 15.0
Motion (MPC): 3.5″/hr  toward 256 degrees