Wednesday, December 20, 2017

Meet Miranda

Miranda - October 26, 2017 - 00:40 UTC Compared to Graphic Generated by JPL Rings Node

   While you may not have heard of this diminutive moon, I have been attempting to capture it photographically for over three years.  You might even argue that I have yet to image Miranda. It is difficult to see huddled close to its brilliant primary. Clearly imaging Miranda is no easy task. However, with a little patients and a lot of image processing, Miranda can be coaxed out of the pixels of an amateur CCD camera.

Miranda - Voyager 2 Mosaic - NASA Jet Propulsion Labatory

     Miranda is the fifth largest satellite of the seventh planet. It had its fifteen-minutes of fame way back in 1986 when Voyager 2 reconnoitered its system. Miranda stole the show boasting a patchwork of smooth un-cratered terrain, an odd “Racetrack” of 12-mile deep valleys and sheer cliffs towering more than three miles into the sky.

     Unfortunately, The Challenger Disaster soon wiped Voyager 2’s discoveries from the news, and Miranda was soon forgotten.

     However, I never forgot Miranda.  Since childhood, I have found planetary satellites fascinating. While other astrophotographers strive to capture the beautiful colors of The Trifid Nebula or the majesty of a spiral galaxy, I dig deep into my images to coax the few photons that I have captured from a distant ice ball. Never, did I believe I could actually image twenty-four of these planetary moons. 

Miranda is The Third Moon from The Left. - Mc Donald Observatory - 1948

     At Magnitude 16.6 and always girdling its 5th magnitude primary, Miranda is impossible to see and a challenge to image. It required an 84-inch telescope to be discovered in 1948. How could I have the audacity to attempt to recreate this feat?

     Although I attempted many times to image Miranda, last October, I had a lot going for me. Observing from 29°N meant, placed Miranda 10° higher than I had ever attempted to photograph it. Likewise, I had a larger telescope and, Miranda was at opposition. With Miranda at its brightest, October promised to be the best time to attempt an image.

     Miranda can only be imaged when it is farthest from its primary.  Sadly, I know of no software that offers this information. How could I determine the time of Miranda’s greatest elongation?

     As a satellite circles its primary, its speed changes relative to the observer. In general, it will be racing toward the observer at its highest speed when it is at its greatest elongation on one side of its primary. Likewise, it recedes at the highest velocity when at its greatest elongation on the other side of its primary.

     With its “Horizons" website, The Jet Propulsion Laboratory offers a variety of information about observing any solar system object. One of the details available is “deldot.” “Deldot” gives the speed that an object is traveling relative to the observer.

JPL Horizons Results
     Open the JPL Horizons website. Input “Miranda” as the Target Body. It is critical that “Geocentric” be used as the “Observer Location.” Otherwise, the results will be difficult to interpret as the application factors in the speed of the observer on a rotating earth. Once the time-span is selected, results are only a mouse click away.

JPL Horizons - Web Interface

     Notice, deldot reaches its most negative amount (-1.8982607) at 00:40 UTC on 26 October 2017. 
JPL Horizons Results for Miranda
     That is the point in its orbit when Miranda is receding at its fastest and must be near to its greatest elongation.

Rings Node Graphic for the Time of My Observation
     Once the time of greatest elongation is determined, another JPL site, Rings Node - Planet Viewer , may be used to generate a graphic of the system and visualize where the object might be found. Fortunately, on the night of my observation, no other moon appeared on Miranda’s side of the planet.

     Armed with this information, I went out into the field and began imaging.  I used a ZWO ASI224MC camera and a Meade 14” LX 850 for my observations. I acquired 20 images each exposed for five seconds and 20 images each exposed for seven seconds.

     I “2X2 binned” these images. This means that each pixel (each dot) of my image is the result of four (2X2) pixels on my camera. When one uses “binning”, the resolution plummets. However, the sensitivity of the CCD is increased. I needed no high resolution for my Miranda images. Instead, I required maximum sensitivity to attempt to capture light from the faint moon.

One of the images looks like this:

Single Image - 5 Second Exposure

     Although the green color of the primary is apparent, none of its moons can be seen. To coax the moons from the data, I stacked both my group of five and seven second exposures. I used “Registax” to stack the images. Although Registax was created to stack images of planetary surfaces, I use it to find the inner satellites of planets. To date, I have used Registax to image the tiny Martian Moon, Jupiter’s Amalthea and Saturn’s Mimas.

     Stacking the images reveals two of the moons, but not the coveted Miranda.

Stack of 20 Five-Second Exposures and 20 Seven-Second Exposures

     Registax has a “wavelet” function. Wavelets are magical tools that used interference patterns to “blur” images of planets to reveal greater surface detail.  The program processes the black sky, bright primary and faint moon in the same way it processes a bright crater rim and dark shadow. 

Miranda Barely Visible at 5 O'Clock

     With a little adjusting of brightness and contrast, five moons become visible. I wish that Miranda’s image was farther from the overexposed center of the image. Unfortunately, seeing on the night of October 25th left quite a bit to be desired.

Miranda! Stack of 40 Exposures Processed with Registax

     Photoshop may be used to remove the overexposed center and replace it with a second, better-exposed image. However, one begins to wonder when an image has been over-processed and begins to become fiction.

     With this image of Miranda under my belt, I plan to attempt imaging other inner satellites including Jupiter’s Thebe and Pluto’s largest moon, Charon. I will let you know how I do.

     So, there you have the story of my Miranda image. I invite your input.

Keep looking up for clear skies.

Ken Everhart

Thursday, November 30, 2017

Notes from The Field - Stephen C. Foster State Park, Georgia.

Okefenokee Sunset
October 23rd found me and my telescope deep within the Okefenokee Swamp. I was excited. While the alligators watched me set up, the skies unexpectedly cleared and the temperature plummeted. Clearly, I was in for a wonderful night of astrophotography. Little did I know that I was about to learn more about my new hobby than the previous three years of fumbling through taking pictures of the stars.

The Gators' Eyes Reflected The Red from our Headlamps
The first lesson had already been painfully learned. Using the long drive to Georgia to mentally plan my observations, I prepared a long agenda of objects to photograph. I have been visually observing for years. Consequently, I prepared my observing list as a visual observing list. This was a mistake.

Visual observers build long lineups of objects to attempt to spot. Typically, it takes me less than 15 minutes to find an object, take a few notes about the object, philosophically reflect on the object (“Wow! This tiny smudge of light contains a trillion stars, and this light left those stars while the dinosaurs roamed the earth”) and move onto the next sight. Therefore, my observing list typically consist of scores of objects to attempt.

Of course, I built my photography agenda similarly long. With such a nice sky and view of the southern horizon, I planned to photograph dozens of galaxies in unfamiliar southern constellations as well as clusters and nebula along the “Backbone of The Night” – The Milky Way. I was even going to attempt to image Neried, one of Neptune’s far-flung moons.

However, I soon discovered that imaging the heavens is very different from visually observing the heavens. My observing plan was far too optimistic. Even if one plans to stack ten five-minute exposures of each object, nearly an hour of exposures is required. Adding in finding the object, centering the object, exposing flat frames, dark frames, dark flat frames and bias frames easily whittles down an observing list. I decimated my observing plan to five objects each night. Imaging Neried was a pipe dream anyway.

The first object on my edited agenda was NGC 891. Very close to the zenith this evening, NGC 891 is a beautiful edge-on galaxy in Andromeda. It looks like a mini Milky Way. Slewing my scope toward the zenith and utilizing an oversized dew shield, I centered the object in my field of view, took a few test images and set the BackyardEOS application on my computer to acquire 10 long-exposure images. As the click of the camera signaled the start of the first exposure, I broke two important rules of astrophotography.

While my camera obediently snapped its preprogrammed sequence, I left the scope to help a friend with his set up. When I returned, the computer screen proudly displayed the following image. What went wrong?

NGC 891 - Single Image

Distracted by conversation with a friend, I failed to notice the sky filled with clouds. Although the guidescope diligently tried to lock on its guide star, passing clouds distracted its attention. The multiple images of each star are caused by the guidescope losing its lock on its guide star and reacquiring a guide star after the scope drifted.

Never leave your scope for a long period of time, and NEVER, EVER stop looking up. Clouds, obstructions and strobe-flashing aircraft are attracted to the tiny square of sky you are imaging. They will ruin your images.
Although clouds effectively ended that night’s observing, the next two nights promised better weather.

NGC 253 was on the top of my list. Even if I failed to image any other object, I was not leaving Georgia without a good image of The Sculptor Galaxy. 

Many North American observers are unfamiliar with constellation, Sculptor, The Sculptor’s Studio. Likewise, we don’t really think about this constellation’s deep sky objects. However, it boasts one of the brightest galaxies in the sky. From the Southern Hemisphere, The Sculptor Galaxy passes high overhead much like The Andromeda Galaxy passes high in our skies.

Although it passed nowhere near Georgia’s zenith, I took advantage of my southern location to take ten images of the galaxy as it rose to its highest point in the southern sky. After seeing the first image, I know I succeeded in capturing The Sculptor.  Here are the first four images I acquired that night.

The next day, I used “DeepSkyStacker", a free application used to stack multiple images, to stack the best of the images.

NGC 253 - Stack of Nine Five Minute Exposures

Fiddling with the Brightness and Contrast brought out even more detail in the dust clouds of this starburst galaxy.

NGC 253 - Brightened in Deep Sky Stacker
Hubble Image used to Inspire Color

Next, I used the hue and saturation functions of Photoshop to increase the color range in the image. Although color differences could be seen in the original image, I fully admit to cheating. The central hub of The Sculptor Galaxy glows orange with the light of older stars. Meanwhile, the spiral arms are dominated by younger, bluer stars.  I tried to mimic these color difference by com pairing my images to a great image returned by The Hubble Space Telescope.

NGC 253 - Color Enhanced.

A little more tweaking of the brightness gave me a darker sky and a prettier picture.

NGC 253 - Darkened

Finally, I cropped the image to remove that annoying dark bar on the top of the frame.

NGC 253 - Final Product

I am not happy with the resolution. The image appears blurry to me. Unfortunately, the seeing was horrible during my visit.

Another issue seems more artistic than technical. During processing, I constantly felt the galaxy should be placed differently in the field of view. Sadly, I could not return to re-image the galaxy. However, I did learn to spend more time on placing the object in the field of view.

Later in the evening, I was able to capture NGC 1300 in Eridanus.

NGC 6781 – A faint planetary nebula in Aquila

And The Little Dumbbell in Perseus

Indeed, this is a long blog post. At least, we learned five good lessons.

1)  Maintain short observing lists. 

2)  Do your math. Do not attempt to image more objects than time allows.

3)  Never leave your telescope for an extended period of time.

4)  NEVER EVER stop looking up. Watch the area that you are photographing.

5)  Remember aesthetics. Even a technically well-done image can appear amateurish if 
     the object is not well-placed in the field.

I worded this post hoping that it leaves many questions unanswered. The purpose of this blog is to foster a dialogue between all of us. Feel free to ask any questions or leave comments. In the meantime, I will create the next few posts answering the questions I have secretly embedded in my writing.

Meet Miranda

Miranda - October 26, 2017 - 00:40 UTC Compared to Graphic Generated by JPL Rings Node    While you may not have heard of this dimi...