FrankenHub is Created & A Very Minimal Power Supply

Okay, it was Halloween yesterday. In keeping with that I'll show you my replacement for the Pegasus Powerbox that died in Iowa. 

My Powerbox was a USB and Power Hub with the capability of controlling dew straps as well. My replacement would need to have those capabilities.

I already had a powered USB3 hub and a small Anderson Powerpole-based power bus from past tinkerings, so it was only a matter of replacing the dew control capability. A nice little Pegasus Dew Controller took care of that.  Yes, it's manually operated, but that's fine.

The USB Hub is so old it's no longer sold (not a surprise) and now is a 7-port, smaller device.

What was left was how to put it all together. And that's how it became Frankenhub.  I decided the perfect "suturing" was silicone bathtub caulk. Silicone caulk is waterproof, binds to almost anything, remains pliable, and can be removed. As an adhesive it's more than adequately secure when joining two flat surfaces.

Frankenhub is three layers, a dovetail to mate it to the ad-hoc finder shoe on the scope OTA, the USB hub, and then the dew controller on top:

Frankenhub

Definitely not as pretty as the Pegasus box, but it works just fine. What it lacks is software control of the dew controller, but I can live with that.

Wait, where is the power hub? Caulked to the side of my G11 saddle:

Power Bus

Think of this as one of those big bolts in the neck of Frankenstein's Monster.

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Speaking of power, here's a minimalist approach that that could run my gear for several nights in the summer: A 50 Ah battery and cute 12 V distributer:

Power and Distribution

The battery has all the power I need for several nights of summertime imaging. The Distribution box is something I got as a Vine reviewer. Here's a closeup:

Power Distributor

Note that it includes a voltmeter that can be turned on/off, various sockets for charging your mobile devices, and a 3-level light that you could easily cover with red plastic.

The included 50 A Powerpole connector probably couldn't handle the amperage that jolted Frankenstein to life, but it's more than enough for my rig's peak use of  5 A.

 

50 amp overkill

Next time I'll have another Frankenstein that I hope isn't monstrous: the Veil Nebula mosaic, using parts (images) from a few sessions at Eagle Lake Observatory, The Iowa Star Party, and a friend's back yard near Stacy, Minnesota. A real Frankenimage. 

 

First Pass at the Veil Mosaic

I finally had enough data to make a very flawed Veil mosaic. Here it is at 1/5 scale:

Click for 1/5 scale image

And here is the link to download the full-scale image. You can use the cloud site's .jpg to look at it, but I suggest you use your own image viewer. Minor advisory, this is a large image, about 10K by 10K pixels and the file size is 12.5Mb.

You should immediately see some interesting things in the full image, some of which I'll detail here. I'll start with the major flaws (all the images below are at full scale if you click on them).

1) What's the big circular thing?

Bad Flat!

This is in the upper left mosaic panel, and results from improper calibration (using an outdated flat, rookie mistake.)

2) What's all that noise?

So Noisy!

Again in the upper left mosaic panel and comes from not only the poor calibration but also insufficient data.

3) What's with all the black pixels?

Pepper Spray

This is found in the upper and middle left panel; it results from pushing the panel a little too aggressively in one post-processing stage.

4) That green thing can't possibly be right!

Streaks to Left of Center: Not Really Green!

So far as I know there aren't any green nebulae. For reasons I don't understand this feature shows up rather strongly in the green channel compared to the red and blue channels; it's quite strong in luminance. I've seen one other LRGB image of this area, and it didn't have these green bits, so I must conclude something in my processing is at fault here.

The Dastardly 52 Cygni

There was one other flaw I had to skate around. I used the script Star Reduction from Blanshan and Cranfield to perform star reduction. It requires a starless image; this can be made either using StarXTerminator (aka SXT) or StarNet2. I used SXT, and it had a lot of difficulty with Magnitude 4.2 52 Cygni (see above image). It essentially suppressed the northern end of NGC 6960! So I switched over to StarNet2 and it handled things fine. 

Notice that StarNet2 didn't handle it 100% cleanly either, giving it what look like (but aren't) diffraction spikes. Looks kind of cool, I think, but then I grew up as a Newt user.

Now for some positives:

1) No seams. I used Photometric Mosaic, and not only didn't it produce seams, but it avoided the pinched stars that GradientMergeMosaic plagues me with. 

2) Color calibration by SpectrophotometricColorCalibration (SPCC). I can't say enough positive about SPCC. My old workflow made color correction very fiddly, with the result depending on how I felt the day of processing more than any sort of objective measure.

3) Not narrowband. For good reason the Veil is usually imaged in narrowband, but that results in false colors. It's nice to see things more as they "really" are (aside from a Green nebula).

4) Not oversaturated. In my opinion oversaturation is very common now. I've said before that a guiding principle of processing should be that less is more; this idea applies to sharpening, stretching, and also color enhancement. I did bump this a half step using ColorSaturation, but pushing it further seemed like too much of a good thing.

5) Reasonably sharp. Here's a neat feature at the south end of of the East Veil. This looks good thanks mainly to BlurXTerminator (BXT). In fact, aside from the one issue seen in SXT, I think the triad of BXT, SXT, and NoiseXTerminator (NXT) is difficult to beat.

An Optical Spiral That's Probably Not a Real Spiral

   

I suspect this curly-thing at center is nothing more than an undulation in a plane seen edgeways, but it does look fun.

So, with those issues listed above this thing obviously isn't done yet. The other night I shot additional light frames for the two panels that suffered from noise (along with same-night flat frames), and I think I can make sure that pepper spray of black pixels can be avoided.

This means doing much the processing over again, but that's life.

Iowa Star Party Imaging

I'm back from the Iowa Star Party! This is held each year at Whiterock Conservency; the observing field is located about five miles southeast of Coon Rapids, and 60 miles from the center of Des Moines.

2024 ISP had some differences from my previous attendances:

• This year's October party was much more pleasant than the steam baths provided by the usual summer dates. Every night had nice cool sleeping weather for us tenters
• The usual evening banquet wasn't prepared on-site and served in the picnic area; instead it was catered and held indoors at the very comfortable Bur Oak Visitor center. It was moved to lunchtime so that it wouldn't interfere with public night. The earlier time also allowed us to be at the field well before dark
• The field was in great shape, and the addition of a modern bathroom / shower facility was very welcome. I had the distinction of setting up farthest from the bathroom, so it was easy for me to get my daily steps in!
• Saturday night was clear, but the high winds during the day put a lot of dust in the air and really enhanced the brightness of local light domes, which have grown much more prominent in recent years. The low, very dark southern horizon may be thing of the past

But let's get to the imaging.

Friday night I was all set up, polar aligned, and ready. First target was Panel2 of my Veil Nebula mosaic, and the scope was doing its slew, center, and rotate thing. But it never finished because something was causing it to throw errors related to the mount control. 

The usual power cycling didn't clear it. What followed was several hours of swapping cables in and out and trying every other remedy I could imagine. Eventually I started to get the sense that the problem was my Pegasus Powerbox, so I recabled everything to remove it from the USB data flow (it remained acting as a 12V power hub, though). This worked, but it left me with no way to power and control my dew straps. Thank goodness it was as dry as it was, dew prevention was not needed that night or the next. 

To confirm where the fault was, I ran a USB cable to the Powerbox but did not connect anything to its output USB ports. The same errors returned suggesting that simply having the Powerbox as an active USB device was enough to cause the problem. 

I've read that the Powerbox can be harmed by connecting a 12V input line to its Adjustable Voltage port, and I know I've done that at least once recently. The poor Powerbox may have run afoul of Stupid User Error and had finally given out at ISP. Bummer. 

Anyway, I was up and running again and was able to collect light frames for my Veil mosaic.  I got everything I needed for Panel 2 Friday night, along with luminance for Panel 3 and a full set of flat frames. Saturday night I collected RGB for panel 3, along with some frames for the odd object seen in Panel 6 data.

Here is the Panel 2 LRGB result (click to see 1/4 scale version):

Panel 2 (NGC 6974, 6979, Pickering's Triangle, and the northern tip of NGC 6960)

Here is Panel 3: 

Panel 3 (NGC 6995, IC1340, and the Southern Knot) 

I've started to work on the full mosaic and noticed that my Panel 1 luminance frames were badly flatted and need to be reshot. If I can manage that this week, next time I'll have a first attempt at the full Mosaic!

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.