Northern Nights Star Fest Featured a Wonderful Aurora; Trying to Image the Soap Bubble

I've returned from the Northern Nights Star Fest, where I had two solid nights of imaging. The first was cut a little short by a spectacular display of aurora, not that I minded at all. 

Most of the night the northern horizon had been aglow. Not terribly bright, but obviously there with occasional pulses within it. 

About 1:30AM the glow became much brighter and began to expand upward from the horizon. Soon it was bright enough to cast shadows and was casting pillars upward, starting with an intensely blue streak that was initially mistaken for the onset of a Steve event. By 1:45 intense upward pulsing had begun contained within a bright-edge envelope. Pulses were rapid bright and chaotic, and their areal extent grew to encompass the entire northern half of the sky. My impression of them was driving at high speed through very patchy fog, brightly lit by the car's high-beam headlights. The dominant color was the usual pale green, with some reds in more persistent bright patches closer to the horizon.

The impact of the aurora was quite evident in the stream of two-minute luminance exposures I was taking:

Mean pixel brightness during the imaging session.

Notice that in my impatience I started imaging at 9:18, well before the end of astronomical twilight (9:42) and you can see the sky continuing to darken through my 15th frame at 9:43.  At about frame 97 (1:02AM) the sky begins a slow brightening probably due to the aurora. At frame 101 (1:08) the brightening rate begins accelerating. 

I was imaging a 2.5 x 1.7 degree field centered on a point between the Crescent Nebula and the Soap Bubble in Cygnus. At 2 AM this was at about 53 degrees altitude directly west. The bright boundary (a curtain?) began moving through the field at about 1:53AM and took perhaps ten to twelve minutes to fully exit. Once clear of my FOV the field was full of pulsations which gradually weakened.

The period of intense auroral activity in the FOV is better seen in this expanded view:

Expanded view of auroral interaction with FOV; not the frame numbers have been offset by 120 for better legibility

By the end of my session at about 3AM the aurora was gradually dimming but still a strong source of natural light pollution. Because the aurora created nasty gradients as it crossed the FOV I'll have to discard those frames, along with others nearby in time.

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Oh, the image I was collecting data for is being processed (see first results later in this post). I don't have much hope for the target (the Soap Bubble Nebula next to the Crescent), so I'm processing the luminance first to see if I can see any sign of it. I have 118 good frames (not quite four hours) after tossing a handful of poor tracking frames and those around the time the aurora was bright.

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Other NNSF personal news:

This was the first time that I performed on-site collection of flat frames (and dark flats). I used NINA's built-in Flat Master to vary my light panel's brightness. This made it possible for all the frames to be one second exposures. Flat Master collects flat darks for all four LRGB channels. Since these are all at the same exposure time, three of the channels' flat darks are redundant. This means a little time wasted, but since this can be done during twilight no harm is done, and the extra files can simply be deleted.

Power consumption was about what was expected. With the laptop-specific battery powering that, the main battery handled the first night's 5.5 hours of mount, dew, and camera cooling with 163Wh. The second night's 4.5 hours consumed 136Wh.  This averages to about 30Wh per hour of imaging or a continuous power requirement of 30W, which is the number I wanted to determine for planning my energy use. 

Let's apply that to the upcoming Iowa Star Party in the first week of October to see what will be needed. That night there are about 9 hours 23 minutes available for imaging. Let's assume three nights of clear sky, so that's at most about 28 hours of imaging. Sounds great!  28 hours x 30W =  840Wh, which is about 240Wh more than my battery can provide. Therefore, I need either AC or solar for charging. Day length is about 11.5 hours, and let's assume the first and last two hours of daylight is unproductive. That gives 7.5 hours to get that 240Wh. That's 32Wh per hour of daylight if it's to be restored in day, or 16Wh / hour if in two days. I think a 50W solar panel should be up to this charge rate, so I've put my 100W panel up for sale. Now I just need to find a replacement in time for October!

UPDATE: I looked at what was for sale on Amazon and saw that the 50Ah battery I previously purchased was on special with an added dealer discount. By far the simplest solution is to bring a second battery and swap it in after the second night's imaging, or patch it into to my power box through the charging port so the two batteries can operate in parallel, providing almost 1.2KWh. Not only an amazon special, but a 10% off dealer discount, too. I went for it.

As for the laptop-aux battery, it was still at 13.3V rest voltage after the two nights, so it's unlikely to need recharging.

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Just registered for the Iowa Star Party, one of my favorites--when it's not crazy hot and humid as it almost always is when it's in late July or August. I've suggested to them that they might be better off holding it in September, and this year they finally moved it -- to October! The average highs then are around 70 and at night it drops to the upper 40s. That's my kind of weather!

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So how did that soap bubble image turn out?  I think "barely there" is the best I can say. Here's the full field at 1/5 scale:

1/5 field LRGB

Okay, Let's get rid of those stars and look at the central portion of the image:

This is a teeny bit better; the Bubble is at lower left, click to enlarge

It's clearly there and has a hint of the correct color shift toward blue, but it's still nothing close to adequate. 

This is based on 3.93 hours of luminance, and each of the RGB channels averaged close to 1.27 hours. What's this in terms of total exposure time? Adding together all the light frames (there were 233) that's about 7 3/4 hours of photons collected. To my way of thinking it's more like 5.2 (3.93 + 1.27) hours.  Whatever way you slice it, it wasn't enough, and double (or even triple) the time is going to be desired to make this look halfway decent. It might also be useful to take the luminance a little deeper. So maybe this will be the target for the Iowa Star Party?

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One last thing, it seems to me that Donald Trump has only one purpose in life: The feeding of his own Ego.  This is not unusual for politicians (see: Lyndon Johnson) but Trump pushes it to pathological limits. You saw in the "debate" how easily his vanity can be used to manipulate him. This is not a tactic invented by Harris; it's a lesson the world has learned from his interactions with authoritarians such as Putin. Trump envies his abuse of power and would seek to imitate it here, replacing the rule of law with the rule of the iron fist. Because I don't think the Grand Experiment of Democracy has yet to run its full course, I will not cast my vote for someone who seeks to sacrifice it to his need for self-gratification.

Oh, and Trump's policies, particularly toward women, stink.

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That's enough for this post. Have fun everyone! See you in October in Iowa!

Extending USB 3 to Your Imaging Platform, Back to Lac qui Parle, and Amazon Vine Reviewing

I have only the vaguest sense of how USB 2 and 3 differ, but I do know how upgrades can mess up things you have running smoothly. Between mosquitoes and equipment upgrades here is what my relationship with USB has been...

The Shaky Start

In my pre-CCD days I imaged with a DSLR and used PHD for guiding via USB 2 (remember Shoestring Canon-to-USB cables?). The USB 2 sockets on my laptop were so poor that losing connection was a frequent occurrence. Getting Com port numbers sorted was not fun, and I had serious doubts about the technology. 

USB 2: True Love at Last

Everything became USB 2: Mount, imaging camera, guide camera, and eventually electronic focuser. The old laptop was replaced with a new one that had better connection hardware and it all worked wonderfully together. After the 2019 Nebraska Star Party I purchased a portable screened shelter to keep away the bugs, the plan being to use one of the ubiquitous USB 2-over-Ethernet extenders to pass from the shelter to the imaging platform, and it worked. Happiness and bliss were mine!

Coleman 10x10 Skylodge Shelter. It's also useful at night.

Upgrading Woes

Time doesn't stand still; things change. In my case I upgraded imager, guider, and focuser; they all became USB 3. And surprise! The USB 2 extender would no longer be adequate. 

I needed to reach about 15 feet from the shelter to the imaging platform. A USB 3 cable that long is well beyond the suggested length limit, so I needed another solution. There wasn't much to choose from: expensive wireless hubs (ASI Air+ and beyond), DIY-ing together a minicomputer and wifi unit, or a USB 3-over-Ethernet extender hardware solution. I didn't care to spend the $300 or more for wifi and I really didn't want to wade into the issues around adding a minicomputer. And I could not find an Ethernet extender for USB 3. But there was another option...

Active USB 3 Cables to the rescue

Active USB 3 cables use signal amplification to provide greater cable lengths, with the determination of "greater" left to the cable maker. The performance of these seems to be something of a mixed bag. Some people have reported that active cables don't play well with the gear I have from Pegasus and ASI, but I suspect that comes from not supplying power at the imaging (female) end of the cable. The one I bought is 16 feet long, and provides the option for a power input at the imaging end of the cable. 

Active USB 3 cable

The power input posed a wrinkle. Like most active cables the input uses 5V input through a 3.5x1.35mm plug. The source for this power is usually an AC adapter of some sort. This isn't handy in the field unless you have AC--which will not be the case for me. 

My power box is all 12V automotive sockets or Anderson Powerpole connectors, so there's no built-in 5V output. The solution was to use an old 12VDC USB device charger that I had lying around. It's designed to plug into the same automotive sockets that I have on my battery box. Because the charger and active cable combined uses maybe one watt it won't affect my battery's energy budget much at all.

Typical Automotive plug USB charger

What I didn't have is a USB 2 power cable with a 3.5x1.35 plug on it, but Amazon had that, too.

The short cable between charger and active cable

The end of the active cable can be strapped to a tripod leg and then a short USB3 cable runs from it up to my Pegasus Powerbox for distribution.

An indoor test of this with everything running under the guidance of NINA was perfect. The powered cable had no issues with any of my things, Pegasus electronic focuser, ASI 2600 CCD, or ASI120 guide camera. The mount was happy with the USB 2 carried on the cable, too. NINA collected 57 images, and downloaded them all plus continuous PHD2 frames without a single fault. A test under the stars is needed, though, since that will add guiding instructions to the data flow.

This is a timely fix for my upgrades, because at the end of July it's time to go

Back to Lac qui Parle

Yes, despite the storms of my first night there, I've reserved 3 more nights at Lac qui Parle near the end of July.

I can't decide on the imaging target for this jaunt. I should probably finish my Veil mosaic, but I'd rather do that from Eagle Lake. How about a two-panel mosaic of the Lagoon and Trifid Nebulae? Both transit around the time it gets sufficiently dark for imaging, so I can avoid the dreaded meridian flip and the minor glow of Montevideo in the southeast. Given the limited altitude of these targets it will be one one panel per night. 

Do you think I can get two clear nights out of three? Me neither.

Speaking of Amazon....

I've been a regular reviewer of the things we've purchased from Amazon and apparently that tripped their AI into thinking I should be a Vine reviewer. Vine reviewers are the ones who get their reviews tagged with "Vine Customer Review of Free Product." Basically we get products for free in exchange for a timely review. The catch is that the value of the product (as given by its possibly inflated retail price) is treated as taxable income. In my wimpy tax bracket this means almost everything I review is mine at a crazy large discount.

Thank goodness Vine allows me to choose what I will review. Most of the products offered on Vine are things that I probably would never need nor want. For example right now there are 75,468 items available for review. An awful lot of them are odd-looking cases for cell phone models I don't own, silicone ice cube molds, and other things of doubtful value, so a wise reviewer must hunt a little. 

It also helps to not play Amazon's game of trying to be a Gold Tier Vine Reviewer. The gold tier requires one to make a lot of reviews in exchange for being offered items over $100 in value. As one Redditor commented, his obsession with maintaining gold tier status was filling his house with shipping boxes and the stuff that came in them. I'm quite happy to remain a peasant in the silver tier. Actually, if there was a tin tier I'd be cozier in that.

But Vine can be useful because every now and then something of interest gets listed, and if you can grab it before someone else it's yours.

My lust for lithium is leading me to glom onto small LiFePo4 batteries that are great for camping. I've now collected four batteries, and will probably add more. A couple of them will be dedicated to augmenting my laptop's battery. Another will power my camp fan for those hot, breathless days and nights. Depending on how many more of these I score I may bring some up to Northern Nights Star Fest as swap meet fodder. Oops, no. Vine rules say that items must remain mine for six months.

Another Vine offering I may use for astronomy is one of their large table covers. These are waterproof, silvered on one side, and have tie-downs. Does that sound like a tarp for covering an imaging platform? It sure does and for a cost to me of about $10. I'll let you know how it works out.

Table cover fabric (note silver interior lining)

Table cover black side out in conventional use

First Image from Lac qui Parle State Park

I finally made it to one of the state parks I had found: Lac qui Parle, northwest of Montevideo, Minnesota, and a little under a three hour drive from home. It was only an overnight stay; I was gone from home for less than 22 hours! I had reserved two nights but cancelled the first because of clouds and rain. Had I known what would happen the departure morning I might have driven home in darkness instead of waiting for dawn. I'll get to that later--for now I just want to talk about the park and the image that resulted.

The Park

Camping is in the Upper Campground.  It has quite a few back-ins, a few pull-throughs, and even cabins. There's a modern restroom and most of the spots have power. I opted for a spot with no power, indicated by the red star in the picture below. Horizons are excellent in all directions, so long as you're imaging at a reasonable elevation. There is a light dome from Montevideo about 10.5 miles to the south east, but it only extends upward about 20 degrees. It should only be a factor if you're horizon-scraping in that direction.

The sky is much darker than at MAS's Cherry Grove field. The Milky Way rose while I was imaging, and it was almost as visually spectacular as it is at the Nebraska Star Party.

LqP Upper Campground (N is up). My location is marked by the star.

The nicely modern (flush toilets!) restroom's inside lights activate using motion sensors (good) but the pole lights just outside are always on (bad). They are boxed, but could be a problem for visual observers. The same building also houses showers.

Each pull-in includes a picnic table, fire ring with grill, and one small tree that provides a little shade and is easy to image around. A bonus is that the ground has been leveled. I set up my tripod and was pleased to see that no manual leveling was needed.

If you want to image from LqP, here are few things to know:

• Reservations are required. Although it does look as if you can make same-day reservations at the entrance if you have a phone (be sure to call and confirm that). My phone, using AT&T network, had nice signal strength.
• All state parks enforce "quiet time" from 10 PM to dawn, so no generators may be used during that time.
• The water from the spigot was a little cloudy; I filled a couple of water bottles from it and saw sediment form in each. The water tasted fine but you may wish to bring your own.
• The nearby park office closes at 4 PM, which is also check-in time. If you have reservations you can go directly to your spot. Just bring a copy of your reservation to put on your dash in case a park ranger visits. They didn't bother to check the night I was there.
• Given the wet spring, I thought there would be a lot of mosquitoes. That evening it was almost all gnats and small black flies until around 10 PM, then the gnats went to bed and the mosquitoes started their shift. While they weren't as bad as I anticipated, I was glad I brought along a lot of repellant.
• Directions: Getting to the park from the Metro area is easy. Chances are most of your miles will be on MN 7, a nice highway once out of the Twin Cities. You can bypass Montevideo by turning north onto county 6 eleven miles past Clara City, then 5 miles later head west again on County 13.  At the Lac Qui Parle Recreation Area a right turn onto County 32 will take you to the campground.

The Imaging 

Everything ran flawlessly by itself for the entire session, lasting three hours and 17 minutes from late twilight until the clouds rolled in. That was a first for me!

Every single light frame was great, 89 of 89! Typically I have lost 10 to 20% of my frames. This kind of perfection was also a first for me. I think the ASI 120MM Mini guide camera has solved my guiding problems that were the main cause of lost frames.

NINA's advanced sequencer handled target acquisition and centering, periodic refocusing, and dithering perfectly. 

In the past PHD2 has occasionally squawked about dithering timeouts. Not this time.

Battery talk: The session was powered by my new 50Ah LiFePo4 battery and it said that the session needed only 145 Watt-hours, far less than I expected. Dew control was only used for one hour, though.

It was a great night, even if I had nothing to do!

Now the image. Here is a much reduced version:

vdB 152 and others (click to enlarge)

The full scale image and the usual gory details are at AstroBin. (Attention: AstroBin imagers! This park is in the AstroBin database for you to select.)

I chose this target as a test of the sky, and I'm not disappointed. It's a positive riot of faint nebulae, layers of gas and dust, and nice bright stars. This is why we love dark skies!

The Morning After

Let's just say things could have gone better if the weather forecast of a pleasant morning had been a tad more accurate. Instead I was awoken around 7 AM by thunder and the sound of hail pounding my metal table. Then the wind hit and my two-person tent bowed almost flat on top of me. I got out of it quickly and was greeted to light rain and small hail. The storm that had hit me was receding to the east but another was fast approaching from the west, so I broke camp by tossing everything into the car and started the drive home. The torrential rain resumed and continued to fall on me all the way back; it was not a fun drive.

Luckily something about the way the clouds had popped up during the night prompted me to put most of the gear into the trunk and a tarp securely over the mount; nothing was harmed, although my car has a few minor dents.

And in the "adding insult to injury" department there was this: the storm had not deterred the morning shift mosquitoes and they were ravenous. I think almost all the bites I got during the stay were in that mad 15-minute rush to pack and leave.

But it was worth it.

Smoke and Solar Eclipses; FocusCube3 Prep; A Target for June

We've had our first smoke event of the year. It came on May 12, six days earlier than it did last year. Even so, I'm hopeful about this summer's imaging. (You can use the Fire and Smoke Map to get a feel for how much smoke there is around, and track your air quality.)

While the dense smoke was bad for visibility and health, it was also remindful of the recent solar eclipse. The dimming of light by the thick smoke layer above our heads reminded us of the sunlight shortly before and after totality. Was this a reasonable comparison?

I guessed the smoke-filtered light resembled sunlight about 20 minutes before (and after) totality. The fraction of illumination 20 minutes before totality is given by this table from a 2009 paper by Können and Hinz:

Column c at 20 minutes before totality gives (with a little interpolation) sun brightness of about 27.5%. We have to use column c instead of the geometric obscuration (column b) because of the sun's limb darkening.

My wife was tracking the eclipse a little differently and she estimated that the smoky sunlight corresponded to when the sun was about 2/3 geometrically obscured. The obscuration column says that 67% obscuration takes place about 22 minutes before totality with a brightness level of about 30%. Both our estimates agree very well (22 vs 20 minutes, 30% vs 27.5%). 

Some years ago -- the early 'aughts, I think -- I was at a dark sky site trying to work my Binocular Messier list and there was heavy smoke overhead. I estimated the extinction it caused at about 1.5 magnitudes. A magnitude reduction of 1.5 means brightness is reduced to of 2.512 ^ (-1.5), or 25% of normal. While it's impossible to know how much smoke there was then compared to what there was earlier this month, it's at least close.

So the next time you have a serious air quality situation or a lot of smoke aloft, maybe take a look at what it's doing to the sunlight. You may find yourself pleasantly reminded of the last total eclipse you attended.

(It's worth mentioning that there's one big difference in how the moon and smoke reduce the the sun's brightness: color. Smoke scatters blue light leaving what penetrates to the surface looking redder, while the moon's effect on color is quite small. How much this plays into one's perception of the dimming is an open question!)

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One nice feature of NINA is its ability to use filter offsets. Offsets let you change from filter to filter without requiring time-consuming manual or automated refocusing; only occasional refocusing using a reference filter is needed. This can potentially save enough time for collecting more data.

Given that I have just replaced my FocusCube2 for version 3 I though it time to update my offsets. This process basically works in a few steps:

1. Obtain good focus manually 
2. Move the focuser until you see a significant increase in star diameters, perhaps 25 to 50%. The distance focus moved will be the autofocus step size
3. Return to the best focus setting 
4. Start the offset determination process using the Darks Customs plug-in.

Before beginning I noticed that my focuser travel (a tiny 30mm) corresponds to about 8000 FC3 movement steps. This is the same as it was for my FC2, so I made a guess the autofocus step size will be the same, too. That let me skip the above steps 2 and 3. The filter offset calculator worked perfectly, and gave me the new offsets: L = 0, R = 11, G = -6, and B = -4. The old offsets were L = 0, R = 7, G = -6, and B = -1. The changes are insignificant compared to the autofocus step; Even the filter order that minimizes backlash is the same.

Incidentally, the focuser performed perfectly during the offset calculations -- every run produced a perfect 1.0 hyperbolic fit. Nice work, Pegasus!

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My first imaging camping strip is scheduled for June, and I've selected the target. If somehow it manages to be clear I'll be imaging VdB 152 ( bright blue reflection nebula), LBN 538 (a colorful emission nebula) and possibly LBN 528 (the faint, dusty "tail" of the reflection nebula). All three are in Cepheus and fit nicely into my FSQ's field of view.

Mosaic Detours and a small surprise

 The mosaic is coming along, but there have been several detours along the way.

That difficulty I had with my guide camera resulted in too many bad frames in two of the panels' luminance and red frames. Why those two channels?  I think it's mainly because of how they fall in the filter sequence, but it could just be chance. These will need to be reimaged, meaning no finished mosaic until later this year.

Something was wrong with my luminance flat frame, too. It was leaving a large light circle in the calibrated images:

Lacking a time machine that could let me reshoot the flats as they were at the time the light frames were collected, I opted to create a synthetic flat of sorts by using PixInsight's ABE. This worked well enough, leaving only a few dust motes to be cleaned up by CloneStamp.

One last issue was a sort of swiss-cheese texture produced by the script StarReduction and by StarXTerminator. This was minimized using CurveTransformation twice: first to reduce the brightness difference between the "holes" and the "cheese," followed by a mild stretch to de-emphasize the background.  You could probably use a masked application of MLT to deal with it, too.

Here's a comparison between the starry original and the final reduced star version

Before

After

Vastly better, I think. Here is the portion of the workflow that is used to take luminance from star-filled linear integrated to nonlinear with fewer and smaller stars:

1. Open the original calibrated, aligned and integrated image (it's still linear at this point)
2. Delinearize the original using STF and HT, save as "NL"
3. Open StarReduction script, set target to NL and click the "Generate starless view" button. If you have both StarNet2 and StarXTerminator installed you'll be asked which to use and what options there are for it.  (I used StarNet2 with a 2x upsample.) When that's completed, close StarReduction and save the new starless image as NL_Starless
4. Enhance NL_Starless as you see fit. Certainly make cosmetic repairs. I sharpened it with MLT using layer biases (layer 1 = -0.2, layer 2 = -0.1, layer 3 = +0.15) Save the result as NL_Starless_Enhanced.
5. Reopen StarReduction, set target to NL, starless view to NL_Starless_Enhanced. Choose the reduction method and any associated parameters, and write them down so that they can be used for the other panels. (I used the Transfer method with a scale factor of 0.1) Check "Create new star reduced image" and if you want to use PixelMath or some other means of combining the stars and starless data check "Create 'reduced stars only' image".
6. Click the green checkmark to apply. Save the resulting image as NL_ReducedStars
7. If your image suffers from "Swiss cheese", deal with it now. Save the result as NL_Done. 
8. This isn't actually "done done." It will need cropping and normalizing before it becomes part of the luminance mosaic.

The settings you choose for MLT sharpening, StarReduction, and possible 'cheese' removal will depend on many factors, so play with them to see what what works best for you. It's probably a good idea to create and save process icons once you've found settings you like.

Lessons learned: Shoot flats ASAP after imaging. Inspect light frames ASAP after imaging to see what you collected.

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Here's the surprise in panel 6 containing the southern portion of NGC 6960:

Panel 6, luminance, starless version

Look in the lower right corner, that thing that looks alike a ball on a stalk. At first I thought it was an artifact, so I looked at other images on AstroBin. I couldn't find it in any of the images there. Astrometry.net didn't ID it in a plate solve, either, so I went to NINA's Framing Assistant where I could quickly see the area in several surveys. This is what it looks like in the downloadable image files:

Panel area from NINA

And there it was. It shows up in the Nasa Sky Survey and HIPS 2, so it's real and not an artifact. But what exactly is it?  I processed my color frames and got this:

Panel 6 RGB composite

It's got a bluish tinge to it, so my guess is that it's a very faint reflection nebula. So far as I can find it doesn't have a designation. Is there anyone out there who can ID it?

Mosaic Workflow

I've been working on my Veil Mosaic project and here is the first tentative result, the luminance mosaic:

Original Luminance Mosaic

The full scale version of this is 10257x9687 pixels in size! This has a number of issues, but it really was just an exercise in stitching together six panels. That part worked flawlessly. The main issue I have with this is the stars. There are just so many of them that they obscure the nebulosity. The other issue is how to extend my workflow to incorporate the chrominance channels and deliver a full LRGB mosaic.

Most people suggest building an LRGB mosaic from channel mosaics, so that's what I will do. As for the mosaic-building tools, advice is mixed with most people indicating a preference for GradientMergeMosaic. My experience with GMM has been disappointing; many of my images include dense star fields, and GMM has had problematic issues with stars at the edge of panels. Instead, I'll use PhotometricMosaic.

The workflow might go something like this for each panel/channel combination, although the last two steps operate on channel or panel groups. It's assumed you've already created master frames for dark, bias, and flat frames.

1. Cull bad images from light frames (Blink)
2. Calibrate light frames (ImageCalibration)
3. Clean up residual hot pixels (CosmeticCorrection) 
4. Assess calibrated frames for quality and select reference frame (SubframeSelector)
5. Align light frames (StarAlignment)
6. Integrate light frames (ImageIntegration)
7. Sort all the resulting frames by panel; for each panel group use DynamicCrop to insure all the channel images for a given panel cover the same sky and have no edge artifacts from dithering. This insures the channel mosaics have identical dimensions and won't require aligning.
8. Background correction (ABE, DBE, or both)
9. Reduce noise (NoiseXTerminator)
10. When all this has been done, sort the panels by channel. If you're archiving images, this is a good time to send all the intermediate products off to storage, they're no longer needed. Only the images from step 9 will be needed.

Because the luminance images will become pseudo-masks for chrominance they need extra attention. Do these steps for each luminance panel:

1. Create a starless version (StarXTerminator or StarNet2, both have strengths and weaknesses)
2. Enhance the starless image (MultiscaleLinearTransform, UnsharpMask, NoiseXTerminator, etc.)
3. Reduce star bloat (StarReduction), apply the same reduction to all luminance panels.

Care should be taken to insure all the enhancements and applications of StarReduction are identical. This is an opportunity to learn how to use PI Containers.

Within each channel, normalize the images using LocalNormalization. The hope is that LocalNormalization will deal with background disparities and that the splining of PhotometricMosaic will make any remaining issues imperceptible. 

Next, create the channel mosaics by repeating these steps for each channel. 

1. Plate solve each panel (ImageSolver)
2. Register each solved panel (MosaicByCoordinates)
3. Merge the panels (PhotometricMosaic)
4. Reduce noise again (NoiseXterminator)

After you've done all four channels you're ready to combine them all as you would any single LRGB image. 

Taking the channel mosaics nonlinear requires you to try to stretch them in roughly the same manner, perhaps starting with the luminance mosaic and applying that same stretch to each of the chrominance channels. PI lets you do this using the STF process. Having done that you're ready to combine the channels and get on with color balancing, etc.

Notice I'm not using the usual PixInsight noise reduction and deconvolution processes. I think NoiseXTerminator provides superior noise reduction and the PixInsight Deconvolution process? I have never had any real luck with that thing. If your stars are round you're better off using StarReduction, which works exceedingly well and is free, too. Here is a too-quick application of StarReduction:

One pass of StarReduction

This image shows the effect of a single pass of StarReduction. There are a lot of blockish artifacts in this resulting from StarXTerminator being applied to the mosaic rather than individual panels.

With this workflow now defined I can get on with the processing!

Getting Out of Town, but to Where?

This post is going to be an exercise in overthinking a simple task like combining imaging and camping, much like the many posts I've made about batteries and such. Wander in at your own risk. 

🌲🌳🌲🌳🌲🌳🌲

Last time I said this post would be about some parks I visited in the hope of finding a nice dark place at which to image and camp. Here are the results of that little jaunt and the realization it forced upon me. 

• Cedar Hanson County Park near Trimont: Very nice for campers, but too many trees
• Sands Country Cove campground southwest of St. James: High density, packed even in April, which is not the nicest month to tour Minnesota. Reservations will be tight, just like how it packs the RVs together. It looks like it caters to families with big RVs. On the other hand, no trees.
• Eagle's Nest County Park east of St. James: Needs a variance to park away from trees in an open pasture that's probably dedicated to horse riders. I've written to the county parks person about that variance, but this is a "light green" light pollution area so not much darker than a local site.
• Voss Park, Butterfield: A large area of trees was removed and sites added since my last visit. It's also not much darker than a non-camping site I use now.
• Lake Hanska County Park, north of La Salle: Too many trees.

Yes, that's correct, none of these were suitable.

Related: An article by the Dyrt.com reports on a poll of 7000 campers. One result was

"In 2023, 45.5% of campers reported difficulty booking a site because a campground was sold out. It was four-times harder to find an available campsite to book than it was in 2019, when just 10.6% of campers reported difficulty."

Here is the realization: Campground reservations are a necessity. Sure, some campgrounds say they are first-come, first-serve. Theoretically you can see a good forecast in the morning, hop in the car and drive three hours to one of those campgrounds hoping there's an available spot for the night. But the chances are that spot will be gone by the time you get there, meaning you have to turn around and drive three hours back home. Not good. Minnesota state parks do allow same-day reservations, but your chance of that working in your favor seems particularly small if you want more than one consecutive night.

 

The problem with advance reservations is the same as that with multi-day star parties: the weather. You can't know what you're going to get.  But unlike star parties with registration fees and associated travel expenses, camping reservations do give you an out. You can cancel the reservation and get some (or most) of your money back, and then complain about the clouds from the comfort of your own home.

🌲🌳🌲🌳🌲🌳🌲

The Hunt for Darkness

Let's say you enjoy camping and want to combine that with dark-sky imaging as an alternative to attending distant star parties.

Choosing when to camp is easy, just mesh your personal schedule with any time the moon isn't a bother. Then match that to campground availability. 

Deciding Where to camp is a little tougher. If you live in a light-polluted city you'll probably need to drive one to three hours to find dark sky.  That means you should think about what your daily safe driving range is. That's the amount of time you can stay alert and your back won't punish you the next day. For me, old and decrepit as I am, that range is about six hours. For the rest of this post I'll assume a driving range of half that -- three hours -- because that permits turning around and returning home if a crucial item was forgotten ("OMG I forgot the counterweight!"). 

With your driving range decided you can start your hunt for campsites that are reasonably dark, accept reservations, and have open sky. And I do mean hunt because campgrounds satisfying all three conditions seem to be rather rare. Some camp sites may be dark enough overhead but have troublesome horizon light domes from nearby cities in the direction you want to image. Many camps are full of shade trees that block the sky. Some like to maximize land usage by packing large RVs so tightly together that they obstruct the sky. Some are near major highways and almost impossible to book. Some are rather primitive. Will you need power and water? Flush toilets? A shower? Everyone has a particular set of requirements.  If you need to run a generator after 10 P.M. you may have issues with a campground's quiet time. And some smaller parks are just sort of unkempt or creepy, making you wonder if they're a "party park" for locals (see for example, Pine Ridge Park north of Herman). Your hunt is for a camp where you can securely image and enjoy yourself while doing so.

It's almost May now and places are taking reservations: it's time to get site hunting. For this post I used Google search, Google Earth, Google Maps, and Light Pollution Atlas 2006 (selecting the 2022 overlay). Google Earth showed me if the locations are infested with trees, Google Maps provided directions and drive times, and the Light Pollution Atlas was great for figuring out how dark a site is and what the horizon situation might be.

Other online resources that were helpful included Minnesota's state park finder and a map of Minnesota's counties. Googling a county name will point you to the county's home page, and from there you can see what it has for parks. A few counties structure their web sites as if they don't want anyone to know they have parks, so be ready to dig.

There are a lot of campground finders on the internet, two that seemed useful are Hipcamp for smaller private camps and The Dyrt for pretty much everything else.

My personal site hunt was limited to the south and west of the Twin Cities because I enjoy that part of the state and it's less tree-infested than elsewhere. You're free to hunt wherever you want. But first we should think about just how dark we want it to be.

☆★✨🌟✨★☆

What is Dark Enough, and What is Too Dark?

I know, I know, there's no such thing as "too dark."  But there can be a dark so dark that it can't be reached within your driving time limit.

My very subjective take on "dark enough" is based mainly on my past imaging at different sites. 

First a bit of terminology: the Light Pollution Ratio, or LPR. LPR is the ratio of light pollution to natural sky brightness; an LPR of 1.0 means that the light pollution is equal to the natural sky brightness. The smaller the LPR the darker the sky. (The Light Pollution Atlas gives you the LPR when you click on its map.)

The diagram below shows an LPR diagram from the Light Pollution Atlas 2022 overlay. The area covered is from near the South Dakota border at left to a bit past Eau Claire WI at right, and just south of Duluth at top to Albert Lea at bottom. Color indicates LPR value with light green being between 0.6 and 1.0; dark green is 0.33 to 0.6. I've changed all areas with LPR greater than 3 to black.

Light pollution map of southern Minnesota. Click to enlarge! 

My back yard has an LPR of 24.5 (!), which is emphatically awful. If I want to image emission nebulae it's narrowband filter time. LRGB imaging (my preference) works well from Eagle Lake (LPR 2.34, EL on the diagram) and Starhome (a friend's back yard, LPR 2.9, SH on the diagram). They're both on the fringe of the Metro and suffer from its huge light dome. Cherry Grove (LPR 1.08, CG on the diagram) is located south of the cities and is very good overhead but less so northward and to the southeast. A person I corresponded with during my Astronomical League Bright Nebula imaging years was using LRGB from a Missouri site with an LPR of 0.6 and his images were nothing less than excellent. I've also imaged from locations where the LPR is under 0.2 and can attest to their excellence.

My take is that an LPR > 7 or so will push you to use narrowband or at least multiband filters. An LPR < 7 is probably dark enough for LRGB imaging of most targets, and an LPR < 0.6 is great for almost any DSO. If you're planning to go super deep, like imaging IFN, then you probably want it as dark as possible to reduce your total exposure time.

My hunting goal will be to find locations where the LPR is 0.6 or less; my motto will be "Go Dark Green or Stay Home." You may be willing to accept something brighter, or demand even darker based on your imaging gear and targets.

Once I determined my personal "dark enough" I could perform my hunt. What follows is the result. See the summary at the end of this post for campground LPR values, links to the individual parks/campgrounds, and other comments.

Minnesota State Parks

Minnesota state parks are widely regarded as some of the nicest in the country. The facilities are well maintained and staffed by knowledgeable outdoor enthusiasts. And lucky for us there are two parks that may be particularly suitable for imagers!

Not suitable -- either too bright or blocked sky: Big Stone Lake, Blue Mounds, Camden, Flandrau, Fort Ridgely, Glacial Lakes, Kilen Woods (probably), Lake Maria, Minneopa, Minnesota Valley, Monson Lake, Myre Big Island, Sakatah Lake, Sibley, Split Rock Creek

 

Suitable: Lac qui Parle and Lake Shetek.

Lac qui Parle is a little darker than Lake Shetek but Montevideo to the southeast maye put up a light dome. One person who has been there said he did not note any problem with the horizon. The positions of these parks are indicated on the diagram above. Both parks can be found in its lower left corner.

All state parks require reservations.

Minnesota County Parks

County parks operate on generally lower budgets and their facilities vary widely. Even so, they will likely be packed full of campers during summer. An additional factor for these parks are monthly and seasonal campers who will fill spaces semi-permanently. A brief look at County parks shows a few promising locations:

Jackson County: Sandy Point (reservation required, choose site carefully to avoid trees, needs a visit to verify horizons)  

Murray County: Sundquist, Lime, and Swenson (no reservations)

Lincoln County: Picnic Point  and Norwegian Creek (reservations required)

Lyon County: Twin Lakes (reservations required)

Yellow Medicine County: Timm Park. Needs a visit to see which if any sites are suitable. (reservations required)

Counties that have no suitable county parks are Blue Earth, Brown, Chippewa, Cottonwood, Faribault, Freeborn, Kandiyohi, Martin, McLeod, Meeker, Mower, Nicollet, Nobles, Pipestone, Redwood, Renville, Rock, Sibley, Swift, Watonwan 

Minnesota City and Town Parks

Many small cities and towns have parks that offer camping. These are generally near the population center and so will have considerable light pollution. I found none that were satisfactory for imaging. 

Private Campgrounds

I am omitting campgrounds that pack RVs tight together; giant RVs are as opaque as trees. 

All of the following locations need to be visited to assess their suitability.

Camping on Private Lake. This was found on Hipcamp. It has an LPR of only 0.3! You would need to talk to the owner about being able to set up away from the trees. If you don't need AC power siting might be easier. Reservations required.

Camp Summit in Hadley. Seven sites, accepts reservations, but also allows space-available. LPR = 0.45

Talking Waters in Gary, SD. Many sites, requires reservations. LPR = 0.51

Niemackl Lake near Herman, MN. Accepts reservations by phone. LPR = 0.26. I visited this a few years ago and found maybe 3 or four of the 10 sites were decent. Neimackl has the distinction of being the darkest campground in my survey!

There are a few places in northern Iowa that look very good, but they are generally about 3 hours distant and will be very busy.

There are probably other suitable private campgrounds. If you know of some please let me know.

Summary: The Too-Short List of Suitable Campgrounds In SW Minnesota

This omits campgrounds that need a visit to judge suitability. (Trees look bigger in person than on Google Earth!) 

Reservations required:

Lake Shetek S.P., LPR = 0.52, use only the Sunrise Campground

Lac qui Parle S.P., LPR = 0.37, use only the Upper Campground

Twin Lakes C.P., LPR = 0.43, only north portion can be reserved at this time

Picnic Point C.P., LPR = 0.42

Norwegian Creek C.P., LPR  = 0.51

Reservations not accepted:

Sundquist C.P. , LPR = 0.35

Lime C.P., LPR = 0.43

Swenson C.P., LPR = 0.41

If you have experience imaging at these or others, let me know how you liked the location!