The Pixel Sweet Spot

Earlier this week the forecast was for an evening of average to perhaps better than average seeing with cold (but not biting) temps. I rolled out the scope a little before sunset to begin cooling and got things ready - with Jupiter just past quadrature it is always going to be highest in the sky as soon as it becomes visible. 

I did the routine alignment, collimation check, and finder alignment before finally popping in the ZWO camera. Activating the camera I was greeted by a strange sight - an emerald green Jupiter. At first I thought maybe a Debayer setting was off in the capture interface but soon noticed that the histogram was not registering in blue or red, only green. I rebooted the laptop hoping maybe that would restore things, but no luck. I brought up a different capture application, but it, too, sported a green globe.

Rather than admit defeat I located my retired Imaging Source camera and popped it into the Barlow. The view and histogram confirmed that we were back to getting a color image, but I immediately was struck by how much smaller the image appeared to be. Hmm - what was that about?

It turns out that my older camera, a DFK21AU042, has a pixel size of 5.6µ whereas my ASI178MC has a size of less than half that, checking in at 2.4µ. The formula for calculating how much sky each pixel registers for your setup is as follows:

  (Pixel Size/Telescope Focal Length) * 206.265  

For my setup using a 2.5x Barlow that becomes:

DFK21AU042 = 0.31"

ASI178MC = 0.13"

The theoretical ideal for planetary imaging for under average seeing conditions is around 0.15" per pixel (Note that this is different than DSO imaging, where the average is about 1-2" per pixel). Clearly, my ZWO camera is a lot closer to the mark, and the better thing to have done would have been to stop and swap out my 2.5x Barlow for my 4x one to get a little lower arc-second/pixel value. But the window of calm seeing that we often get shortly after sundown wouldn't allow that, so I forged ahead.

Below are comparative images taken about a week apart of roughly the same Jovian longitude. It is pretty obvious from it that we lose resolution in the image acquired using the DFK21AU042 camera.

Is the image from the older camera terrible? No, hardly. We can still make out details like Oval BA and anti-cyclone storm A1 - something that was unheard of using film a few decades ago. But in astronomy, and in planetary imaging in particular, it is all about getting all the parameters as ideal as possible so that you can capture all the details available given the seeing conditions. Hopefully I get my ZWO camera fixed, but in the meantime I know from experience now to at least break out the 4x Barlow to try to get closer to that desired arc-second/pixel value.

Frost Moon Eclipse

For the second November in a row, the Moon was scheduled to take a plunge into the Earth's shadow (only this November it'd be a total eclipse rather than a very near total eclipse). With the forecast for the early morning of November 8th being a bit questionable (and not taking the workday off), my plan was to set an early 5am alarm to check the western sky for clouds. The weather gods ended up being kind as I could see the eclipsed Moon hanging low in the sky with minimal clouds. I threw on street clothes, grabbed the camera waiting on the tripod in the kitchen, and headed out to locate a spot along the street with an unobstructed view of the event.

It was chilly but not frigid (50°) with some scattered clouds amid a pretty transparent sky overall (7/10). There was a sporadic breeze out of the north. I took some time to just visually enjoy the sight of the deep orange lunar disk hanging about 10° above the western horizon between a gap in the trees. It seemed to be a little on the dark side as lunar eclipses go, probably a Danjon 2 by my estimate. I thought about how these events are beautiful occurrences to us but that centuries ago they would likely strike fear and dread to the average person. Iconic Taurus and Orion looked on nearby along with brilliant Mars, but the spot occupied by Luna was devoid of visible stars given my Bortle 8 suburban skyglow. 

 

 

I racked the telephoto out to 300mm and worked on getting a focus. I then started firing off a set of shots, altering the exposure time to hopefully get one close to approximating the visual appearance. I then dropped the focal length down for some wide-angle shots before calling it a successful event as the Moon slid further to its approaching western horizon rendezvous.

Downloading the shots to the computer showed that, yet again, I had managed to just miss the desired razor-sharp focus. To me this is the Achilles Heel of DSLR cameras – they excel at allowing multiple photos without worry of film expense and even a digital darkroom, but gone are the days where you could reliably slide the focus ring all the way over to infinity and know that you were indeed focused at infinity. Some of it might have been that northerly wind buffeting the tripod a little, but probably 90% of the issue was my not being attentive enough to the focus.

 

I wonder how many lunar eclipses I’ve now taken in over the years. It would be hard for me to go back and tally them as earlier on I certainly didn’t keep records, at least nothing that survived till now. Whether it’s 10 or 20 I can certainly say that they are one of the most pleasant spectacles that Mother Nature provides.

 

Putting It to the Test

One of the many sections of ALPO^[1] is the Online section, of which I’m an assistant coordinator. While currently this means I’m focused on helping to maintain the organization’s website and post observations to the galleries, I think there can be more to the section.

Born as the “computer” section in response to the PC revolution and its impact on our hobby, the original aim was more towards what sort of software was available to assist the amateur planetary observer. To me, this has more relevance than ever given how integral software has become in processing most observations today.

There are many competing products out there that one can choose to align, stack, sharpen, and tweak their video capture into a valuable image that documents the state of an astronomical body for a given point in time. Less available to the amateur observer is a sense of how the software works or what approach is preferred (or should be avoided). Often the individual approaches it as a bit of a black art, playing with settings in the interface and seeing if the outcome is better or worse. While the learning curve is perhaps not as steep as with something like PixInsight for our deep sky imaging brethren, there are still many nagging questions when doing a planetary imaging workflow – “Am I doing this right?”

This is where I believe that the ALPO Online section has a role to play harking back to our roots as the “technology” arm of the organization by conducting studies to shed light on common questions. As an example, when setting alignment points on an image in preparation for alignment & stacking, what size works best? How important is that? What is the current theory on it, and does that theory hold when tested? Questions such as this are not just academic, their answers can impact the quality of our output.

With all this as background I’m announcing an effort to tackle some of these software setting questions. Lifting a page from the Zooniverse folks, my idea is to generate a set of images where, to the best of my ability, all parameters are the same except for one and then invite the amateur community to score them. With a sufficient number of evaluations, it should be possible to make a statement (and perhaps a recommendation) on the optimal setting to use when processing your video into a final image.

I have defined my first inquiry and worked up a set of images to use in the test. The posit is that when processing a video taken under only fair seeing it is better to use larger alignment points, whereas a capture under very good seeing benefits from smaller sized alignment points. The theory is well explained by Christophe Pellier in Chapter 7 of his excellent book Planetary Astronomy:

“An AP is defined by small boxes and the alignment will be done based on the details that are present inside of it. If the image is noisy and with low contrast, a size that is too small will prevent the software from performing a comparison because of a lack of detail found in some of these boxes. On the other hand, if there is considerable detail present a smaller size AP will increase the accuracy of the alignment.”

Perhaps I am tilting at windmills here in thinking that I’ll get enough participation, who knows? I’m hoping to be able to not just confirm the theory but to also offer some qualitative assessment of its impact on one’s resulting image. If you would like to participate in reviewing the six sets of images, please visit my new ALPO Research & Investigation web page that I am hosting on my personal website until such time that it proves viable and suitable for deployment on the official ALPO website. And thank you in advance for your time if you do decide to participate!

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^[1] Association of Lunar and Planetary Observers

More Than Meets the Eye

Sept 20-21, 2022  

While prepping for my HAL talk last month I stumbled across the fact that the Astronomical League has a Jupiter Observing program among its offerings. It's a program whose objectives I've certainly met over the years, but thought it would be fun to officially claim the prize. 

One task is to collect a series of observations on the 4 bright Galilean moons and interpret your data to characterize the moons and their orbits. You need a couple of sessions spanning over two hours, and this evening's clear skies (and an added bonus of a Ganymede transit) was a nice opportunity to meet some of the program's requirements. I decided to use the 80mm Vixen refractor since it is easier to set up and more than adequate for recording the bright moons.

By 10:30 I had Jupiter centered in the eyepiece. Ganymede's large and stark shadow is not hard at all to pick up on, even in this small aperture. While I could have simply sketch the moon positions, I opted for a set of video images at 30 minute intervals as a better approach. 

Galilean Moons, with Ganymede in Transit

When I finished the first capture I did a quick processing to see what I had. I was actually a little surprised at the detail on the planet using such a small aperture. It led me to wonder just how much detail could I get using the Vixen if I tried? 

Since I needed to wait a half hour to make my next capture I decided to explore the question. I popped in the Meade 2x short Barlow and brought the Region of Interest (ROI) as tight as I could. This smaller capture area allowed the frames-per-second rate to go from 96 to 286, increasing the chances of leveraging those microseconds of steady seeing into a nice photo.

Next day I set to work running the video capture through my workflow - PIPP, Autostakkert3!, and Registax6 to produce a final image. Although the details are puny compared to what the 10" Cyrus reflector produces, they are pretty amazing given the aperture. Not only do we get the major bands, but features such as festoons in the NEB, Ganymede's disk as it begins to egress, and even Oval BA can be clearly identified in the tiny image. 

Would one suggest an 80mm refractor as a good instrument for planetary exploration? Not really - but it clearly has a lot more to offer compared to what you'll see behind the eyepiece when you team it up with computer assisted planetary imaging. Visually it takes a little effort for me to discern Oval BA using the 10" with a suitable filter. Snaring it in a capture using a telescope with 3 inches of aperture is really quite a testimony to the high-contrast quality that refractors offer as well as the power of using the lucky imaging technique. If you use a similar scope as your main tool for exploring the night sky you might consider adding on a planetary video camera and discover for yourself the enjoyment of capturing features that you'll likely never see visually.

Cool Hot Spots

 July 16, 2022

It’s about 3:45 am when the alarm on my phone gradually intrudes upon my slumber, summoning me to an imaging rendezvous with Jupiter that I thought would be a good idea 6 hours earlier. I lay there for a moment and have the internal debate as to whether I really want to do this. A couple of minutes pass and I decide yes, I do want to keep the appointment – it’s worth the effort to see what interesting features might be on display. Donning more appropriate street attire and grabbing the laptop I head out to the driveway where Jupiter hangs like a brilliant beacon above my neighbor’s house. 

I wheel the scope out from the garage and pull off the covers. In my mind I tick down the checklist of tasks to perform before I can begin imaging. Validate mirror collimation, verify spotting scope alignment, adjust weight to achieve balance, power up mount & laptop, connect everything. After a few minutes I fire up the camera and go about getting Jupiter centered in the field.

As I sharpen the focus my attention is drawn to a very dark area along the North Equatorial Belt. Pretty weird – the intensity is almost reminiscent of a shadow transit, but it lacks the crisp, hole-punch appearance that I normally associate with such an event, seeming more distended. I continue my imaging run for about an hour and then break down the setup so that I will be ready for the next session.

Later in the day I turn my attention to processing the video capture into a sharpened image of the planet. As I twiddle with the wavelets I see that the dark area is a projection off the NEBs extending into the equatorial zone, and the color is a pronounced dark slate gray. That combination of information allows it to be classified as a beautiful example of a Jupiter “hot spot”.

Jupiter with "Hot Spot" 07/16/2022

As documented in John Rogers book The Giant Planet Jupiter, these blue-gray areas along the NEB’s southern perimeter have been observed over many decades. Research has found that most of the time there are perhaps a dozen of these features present, spaced roughly every 30⁰ around the planet. From what I have seen from other observers sending in their images to ALPO, these hot spots are far more prominent right now. Looking back over the 2021 images I can catch glimpses of these features in keeping with Roger’s statement, but they were more subtle.

What is a hot spot? Why is it such a different color than we normally see? Current theory holds that these are areas of high pressure (sinking air), and as the air warms in its descent the white ammonia crystals evaporate, allowing us to see deeper into the planet, possibly all the way down to the level where water clouds can form.

We actually have another reason to be curious about these features because on December 7, 1995, the Galileo atmospheric probe actually entered a hot spot and sent back data for almost an hour, finding less water and helium than expected. Understanding hot spots can help us interpret the data from the probe.

Another interplanetary voyager, Cassini, has also helped to unravel the mystery of these hot spots. Images taken by Cassini as it flew past the planet on its way to Saturn have been analyzed, leading to a hypothesis that a Rossby wave is producing them. Such a wave is undulating up and down in the atmosphere, generating a hot spot region as it plunges downward, displacing the colder air. There is a nice NASA video describing the research here. 

While it’s not clear if these hot spots will continue to be prominent for the remainder of this Jovian apparition it’s certainly possible. If you are an imager they should be fairly easy to pick up if you are using a scope in the 4-inch (refractor) to 6-inch (reflector) range. Visually a strong outbreak like this one from July 16^th should be doable in the same size instrument, especially if you boost the contrast by using a red filter. More subtle ones are likely going to need larger aperture, steady skies, and will also be aided by a red filter. If you do record one you might consider sending your observation to ALPO to document it.

Jupiter reaches opposition next month, a great opportunity to spend some time examining its features at a reasonable hour of the evening. Who knows – perhaps you’ll be able to say “Oh course I’ve seen the Great Red Spot, but have you seen a blue hot spot?”

Attempting ADC

 I've attended a couple of sessions within the last year led by renown planetary imagers (Damien Peach, Agapios Elia) in pursuit of what I can do to refine my setup. One thing that both mentioned rather high up on their list was using an Atmospheric Dispersion Corrector (ADC) in the imaging train. The premise is that the atmosphere bends blue light differently than red light, causing a slight smearing of the "white" light we get at the eyepiece. An ADC, which is a set of adjustable prisms, allows you to correct the dispersion, yielding a sharper image. 

I had hesitated on acquiring one, in part because both individuals use large SCT units for their imaging - would a Newtonian benefit? Second, I had assumed (incorrectly) that the amount of smearing would be minimal once the planet got above 30° (see this). And finally, the Autostakkert software supposedly performs a correction for this when stacking.

Autostakkert "RGB Align"

I ended up convinced that it might be helpful so I got the ZWO model which was a past Sky & Telescope "hot product" award winner. The unit arrived about a week after ordering it, and as forewarned by my research, there were no instructions on how to use it. Fortunately other brave souls have sorted it all out and been kind enough to post video tutorials.

The unit is placed between your Barlow and the imaging camera. There are two steps for having it correct the atmospheric distortion:

1. Use the bubble level to ensure that the unit is parallel with the horizon. That will obviously fall out of order as the evening progresses and your scope tracks the planet across the sky, so re-doing this step every half hour or so may be needed.
2. Adjust the two silver levers (on right in picture) in equal but opposite directions until you can no longer detect color fringing 

It is that last step that can be tricky. One approach recommended by Martin Lewis is to overexpose the planet on your screen to make the fringing more obvious. You can then iteratively adjust the levers until the fringing is minimal (or at least you are unable to say which side is reddish one and the other bluish). Many of the imaging capture programs (e.g., FireCapture, ASI Capture) also have a utility to help assess your alignment. In general, when the circles overlap then you have achieved merging the spectrum back into white light. But given how wildly the two circles will bounce around on the screen it is still a bit of a swag. 

Performing ADC Alignment with Jupiter

This past week I decided to give it a go and placed the unit between Barlow and camera. Given the height of my set up, I had to use the step ladder to reach up to perform the leveling and then to gradually spread the levers, constantly referencing the laptop screen to see the impact. Of course another trick is to do it gently enough to not knock the planet out of the field of view. After about 5 minutes I felt the bouncing circles were are concentric as I might achieve. I did a focus and then started a couple of captures.

Sadly, what I noticed about 20 minutes in was that my focus was a bit soft. Looking at the focuser read out I noticed I was racked fully in due to the extra back space the ADC introduced. And sure enough, the actual focus point was just a tad further in. No amount of ADC will substitute for mushy focus, so I pulled it off and resumed imaging with a sharp focus. My task now will be to remove one of the spacers from the Moonlight focuser so that we can get to that focus point with the ADC in place.

Will it all be worth it? Hard to say, but given the feedback from well respected imagers I certainly am committed to finding out. And empirically it makes sense to try to correct this dispersion as the image is captured rather than to depend in post-processing algorithms to fully compensate for the effect. That's the game now - incremental improvement wherever I can achieve it.

Jupiter without ADC - can I tease out more with an ADC?

Fine Focus

For any astro-imager, focus is always a primary concern. When doing deep sky it has to be spot on to get those tack sharp stars that we love to see. Fortunately for DSO imagers, there are aids such as a Bathinov mask that can help ensure you are on the mark.

Bahtinov Mask

 In planetary imaging it is a little more challenging. We also need to be in perfect focus to capture the subtle details, but a Bathinov mask isn't going to work on a non-point light source. Trying to move the scope to a bright star to focus first before centering the planet also seems to fall short. What one is left with is manually fiddling with the focus knob while watching a feature of the planet to get it as sharp as possible. For example, a Jovian moon or the Cassini division are often good targets to pay attention to in this effort.

Unfortunately the planetary imager is confronted with another problem: the high magnification utilized to get the planet's disk to a suitable size. This means that the slightest touch causes the planet to wildly dance in (and sometime exit from) the field. The result is an iterative set of focus-recenter-evaluate attempts until you feel it is as good as you can get (or your patience is gone and you settle for "close enough"). When rebuilding the OTA for my 10" Cyrus¹ Newtonian I even invested in a nice JMI focuser with a feather touch micro-focuser, but it still didn't solve the fallout of a human hand touching the scope.

I finally came to accept that investing in a motorized focuser was going to be necessary to solve the problem. Based on the positive experience Dale Ghent had with MoonLite focusers for HALO, I opted to order from them. It takes a bit of time to go through all the various options but I eventually balanced my desire for bells & whistles with my budget to get a Crayford 2" focuser with their universal adapter and stepper motor for about $700. To my surprise and delight they had the unit to me within about a week.

Next came replacing the existing JMI with this snazzy unit. If you look at their universal adapter, it is "a plate with multiple many different 4 bolt hole patterns for Newts over the years, Meade, GSO, Orion, Celestron, etc." 

 

However, none of them aligned with the existing holes I had placed into the tube when installing the JMI focuser. So it became a tedious process of securing the plate with a couple of openings that did align and then trying to accurately measure where the new hole had to be drilled to accommodate where the opening was on the plate. After a couple of hours the plate was finally secured and motorized focuser attached. 

 

Installed MoonLite Focuser

As you can see from the picture above, this is a substantial unit. It occurred to me that this would probably alter the scope's balance once I added in the Barlow, camera, and possibly an Atmospheric Dispersion Corrector (ADC). In the past the scope had always been a little "rear heavy" when imaging, requiring placement of a magnetic weight along a shelf bracket that runs along the front half of the tube. I opted to install a similar bracket along the back half of the scope, and indeed it was needed to achieve balance when I did a dry run.

A couple weeks later with Jupiter and Saturn getting a reasonable (if not great) altitude in the pre-dawn skies, I gave the MoonLite unit a test run. I did not purchase a separate hand controller to operate the focuser but instead attached it to the laptop using the provided USB cable. The unit also has to be powered - so yet another cord dangling from the focuser that I tried to tuck alongside the scope to avoid any tension or vibration it might cause.

The interface is pretty intuitive, allowing you to move in or out by orders of magnitude. Once Saturn was centered it was easy to display the planet in the video capture software and have the MoonLite Single Focuser app on top so that I could watch the planet as I commanded the focuser to adjust its position. During the process there was minimal movement of the planet and no risk of knocking it out of the field. I ended up getting what I felt was as good a focus as I could achieve and was happy with the result after I processed the video captures the next day (below). 

While the swapping out of the original JMI for the MoonLite ended up being a little challenging in the installation stage, I'm very happy (and blessed) that I could do it because the results are what I was looking for - a far less painful and far more accurate focusing experience. Like so many other hobbies, amateur astronomy (especially when coupled with photography) is an investment. It seems to be a continuous process of identifying what might improve our ability to see or photograph the heavens and then budgeting to make that next upgrade.
 

¹ I call it the "Cyrus" telescope because the optics were made by Charles Cyrus, a friend and excellent ATM from back in my days with the Baltimore Astronomical Society. After Charlie's passing his instrument made its way to me and I have enjoyed it for a couple of decades now, most recently redoing the OTA that houses the mirror.

The Dogs' Globular

Tucked under the Big Bear's tail is the tiny constellation of Canes Venatici, Boötes' hunting dogs. For such a small constellation it might be accused of celestial gerrymandering by having its borders claim such deep sky masterpieces as M51 (Whirlpool galaxy) from Ursa Major and M3 from the herdsman. 

Messier 3 is a wonderful globular boasting half a million suns packed into its perimeter. Even from Towson you can sweep up this dandy DSO as a fuzzy 6th magnitude star roughly midway between Arcturus and Cor Caroli (the α star of Canes Venatici). My 6" RV-6 Newtonian at medium magnification and averted vision shows a brighter core and some of the members of the cluster winking in and out with averted vision. The 10" Cyrus reflector exposes many more suns and begins to hint at the true majesty of this object. 

When planets aren't around for imaging I will give the deep sky a go. In this regard I'm not very hard core, using my  unmodified Canon EOS t6i rather than a dedicated unit, and I have not invested in things such as a field flattener that the more serious imager might do. I also do not currently have a guide camera, relying on a good polar alignment and shorter ~30 second shots to keep stars from trailing. I use a simple illuminated tracing pad to serve as light source for my flats. I have invested in a copy of PixInsight for processing, and will probably be plumbing the depths of its functionality for years to come. So when at the end of April we had a pleasant evening, a little chilly but with pretty good transparency, I rolled the mount out of the garage, attached the Vixen, and set off to see if I could get a nice scrapbook photo of the globular.

One of the things that I wanted to try out was my recently purchased Baader Moon & Skyglow filter to see if it could cut down on the nasty light pollution in my stacked image that I so often encounter when doing deep sky. The company claims "it darkens the spectral region which is particularly marked by street lamp light, which is the biggest contributor to the nightly Skyglow". The second thing I was interested to evaluate was BackyardEOS, a software package that allows you to automate a sequence of exposures taken with the camera. In the past I had turned on the camera's built in Wi-Fi and used the Canon app on my tablet to take the exposures. But that gets tedious fairly quickly, firing off an exposure every 20-30 seconds. 

The time spent on polar alignment was worth it as the scope dutiful slewed over to Arcturus for a quick focus check with the Bahtinov mask in place. From there we slid up to M3 and began the session shortly after the passing of astronomical twilight. The BackyardEOS performed quite well as I set up a series of 30 second exposures over 15 minutes. At the end of each run I would check that the globular was positioned near center and that no star trailing was evident. After 6 such runs I then set about acquiring the dark and flat exposures.

Of course, collecting the data is only half the game. The stack in Deep Sky Stacker looked pretty good when I did an auto-stretch in PixInsight. The light pollution detritus was much reduced, so high marks for the Baader filter doing its job fending off the neighbors' lights. This time, in my search for a good PixInsight workflow, I followed along with a YouTube video made by Richard Bloch. It was one of the best I've watched so far, easy to follow along and enough rationale provided for why you are taking certain steps. It ended up helping me produce a pretty nice image of this cluster of suns that was the first faux comet entry that Messier himself is thought to have observed. 

It is always satisfying to see your work improve, and I was happy to find that my small investment in the two new tools did help me in my desire to occasionally snatch a deep sky portrait from the driveway of my home.

Saturn Shadow Play

Saturn is gradually climbing out of the Sun's glare in the pre-dawn sky, and by month's end it clears 20° in altitude before civil twilight starts. The ringed planet is both spectacular and subdued in the eyepiece. The rings, even if beginning to close up compared to the last few years, are just an amazing sight. The globe, however, is subtle with its pastel colors and gradually darkening bands as you move north to the darker NPR. For this reason most of us will admire the planet for a minute or two before moving on to another target of interest.

A unique aspect to Saturn is the shadow play of globe and rings. The most obvious is the shadow of the globe cast on the rings as they arc behind the planet. Prior to opposition it is seen on the preceding (western) limb, reaching maximum visibility at western quadrature (which will be May 16th this year). It gradually wanes until it is invisible at opposition and then emerges on the eastern limb, growing until reaching eastern quadrature. 

Saturn, a month after opposition, shadow on eastern limb

A little harder to detect at times (and more complicated to predict) is the shadow of the rings falling upon the globe. The geometry is multifactorial in predicting where (or if) we get to see the rings' shadow; the extent to which the rings are tilted and the angle between Earth and the ringed planet can influence it. In general, the shadow of the rings on the planet is obscured when they are "fully open" and then gradually becomes more visible (and thinner) as we head towards Saturnian equinox. 

We're entering the period where the rings' shadow is beginning to peek out along the southern border of the rings. Earlier this month there was an interesting observation submitted to ALPO by Clyde Foster, an accomplished planetary imager from South Africa. In it he noted a bright white speck at the intersection of  the western limb and southern edge of the rings (below). At first he considered it as an artifact, but then Martin Lewis from England postulated that this actually represented us seeing sunlight passing through the Cassini Division onto the planet.

Mr. Lewis' analysis was greatly aided by the tool known as WinJUPOS, a software program that handles the calculations of Solar System object geometry (among other marvelous functions). The graphical representation of Saturn for early April when Clyde made his observation showed that the ring gap was ever so slightly peeking out from under the rings on the western limb. 

Using WinJUPOS to examine the position of the shadow reveals that the "Cassini Gap Sunshine" will continue to emerge from under the rings on the western limb for several more weeks, reaching its maximum exposure as Saturn reaches western quadrature May 16th. It then begins to retreat until it is tucked up under the rings and lost from view by mid-June. The animated GIF below shows the ebb and flow of the CGS. 

Animation showing the Cassini Gap Sunshine (CGS) visibility

I suspect that this might be imaged with a telescope as small as 6" in aperture, and possibly even seen visually. Steady seeing will be a huge determinant in your success, but the good news is that at dawn we often find some of the steadiest conditions and Saturn will be near its culmination in the sky. Also be sure to allow enough time for the optics to cool to the ambient temperature, especially with a Newtonian system. I for one am hoping to see this CGS in mid-May with my 10" reflector and will share any success on the HAL Google Group. 

And, in full disclosure, seeing the CGS should be easier next spring as the rings close up even further. Sure, it's going to require a little effort to see if you can observe or capture this first opportunity at seeing the sunlight filtering through the Cassini Division on the cream-colored cloud tops below. It is guaranteed to test your planetary observing (or imaging) skills to snag it like Clyde. But then again, isn't testing your skills at the eyepiece a part of what makes this hobby an enduring passion for so many of us?