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!)

------------

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!

------------

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.

Panels and Pieces

September update with shouting headlines:

GUIDING WOES SOLVED!

After an August imaging session that featured repeated guide camera disconnects I decided that it was time to move on from my QHY5L-II. I'd read somewhere (CloudyNights?) this was one of its traits. Disconnects have been a repeating problem during its service to me. There have been nights I've retreated to my good old StarShoot Autoguider.

I had tried to work with the camera. It seemed as though the issue was insufficient power, so I used shorter and shorter USB cables, then a powered USB 3 port and a very short cable. The disconnects became less frequent but imaging time was still being lost. 

Something had to be done; I can tell you that it is not fun fussing around at 2 or 3 AM trying to get things going again after a disconnect. So I went all-ASI and purchased an ASI 120MM Mini (mono). My only qualms about the Mini were possible software collisions with my imaging camera, an ASI 2600M, and if it would be compatible with the QHY mini guide scope.

The only camera confusion was mine when I gave PHD2 the wrong camera to use. The ASI120 seems to work well with the QHY mini guide scope, although it may need a little more backfocus. And during an evening of imaging not a single disconnect, so for the moment I'm declaring problem solved. I may swap out the QHY guide scope for my old Orion 50mm guide scope, just for the added aperture.

MOSAIC DATA COMPLETED!

My ~57 megapixel mosaic of the Veil nebula has taken long enough, hasn't it? Panel 1 (of 6) was imaged June 19. Panels 2, 3, and 4 were imaged August 25 and September 11. The final panels, 5 and 6, were imaged September 17. The long summer delay was thanks to smoke, air quality, heat, clouds, and my availability. It's been a summer. 

I don't yet know how good the light frames are of these but they will have to do. Each panel is made of approximately 48 minutes of luminance, and 24 minutes of each color channel. This means it's not particularly deep, but this is the Veil Nebula and hardly the dimmest object in the sky. I could collect more data, but I'd like to move on to other targets.

DISASTER AVERTED, TWICE!

This is how my night imaging the last two panels started....

Disaster #1: The dew strap for my FSQ's objective had a short that I first noticed as a wild variation in the Pegasus Ultimate PowerBox current. It was hopping between a low, reasonable value and 4+ amps as it tried to control the situation. Its control probably prevented the Powerbox's demise, a meltdown of the strap's cable (it did become too hot to touch) and perhaps even damage to my AC to DC power supply. 

Disaster #2: Without the dew strap imaging could last only until I saw dew beginning on the imaging scope's objective. I hoped I'd be able to get at least one of the two remaining Veil panels done but it seemed doubtful. There was no breeze to keep the ambient temperature from cooling rapidly and because I was imaging almost straight up the objective would probably dew quickly.

Maybe it was convection from the power supply and the cooled imaging camera or just plain good luck but it somehow stayed dew-free for the time required to get both panels imaged.

NEBRASKA STAR PARTY 2023: SMOKE AND CLOUDS!

Okay, I didn't attend. I'll sit in judgement of it anyway, partly to justify my staying home but mainly to question the wisdom of traveling to distant places for imaging. Which is not to say I won't go next year, if someone could do something about all that smoke. As for the heat--it's not NSP without a day or two of 100-degree temperatures or hotter, is it?

Here are the day-by-day NSP 2023 imaging conditions as gleaned from the weather service and air pollution monitors.

Saturday Night: red category air quality and terrible transparency. I'm of an age that puts me in the group the air quality people always caution about being active when the air is this bad. We had a couple of days this summer where I live that were as bad as this and the surface smoke was so thick that it looked like a thin fog. Setting up camp was not something I'd have wanted to do in red air. And of course, with the smoke the greatly reduced transparency for imaging negates the point of going someplace dark like NSP.

Sunday Night: Saturday night all over again.

Monday Night (First "official" night of NSP): Clouds and a thunderstorm.

Tuesday Night: Probably clear from Midnight to 2 AM, then rain around 3 AM. Very humid (dew point temperature near 70 degrees) so super uncomfortable sleeping in a tent on the observing field.

Wednesday Night: Partly cloudy all night. 

Thursday Night (my last night at NSP had I attended): Partial clearing around 12:30 AM, then partly cloudy until 3.

So maybe a couple of hours of imaging Tuesday night and again Thursday night; for maybe a total of four hours of smoky sky imaging across six nights. Add to that unhealthy air quality on two nights.

Some years NSP can be a fun vacation in the wilds of Nebraska with very dark sky. Some years not so much. If the wildfire smoke becomes an annual problem NSP will difficult to justify as a travel destination.

On the other hand, with summer smoke affecting most of the region, where else would you go?

That's all for this dramatic update!

The Start of a Mosaic

It's been kind of wild since the last post. We've had many days of air quality alerts, most of which have been for excessive surface ozone, a byproduct of smoke and sunlight and "normal" air pollution. Smoke at times thickened to concentrations similar to what was seen earlier on the East Coast. It wasn't healthy at all; hospitals reported a surge of people with breathing difficulty.

The air quality did improve for a bit and I was able to get out and do a little imaging. In fact, I managed to start one of my learning projects!

One item on my to-image list is a mosaic of the Veil Nebula that spans both the east and west sides. The Veil isn't immense like Barnard's Loop, but it's large enough to require something like a 250mm lens to fit it all in a single frame. My FSQ-106 has a focal length of 530mm and it really needs something like a 2x3 mosaic to encompass the Veil. That's 6 frames, and at about 2 hours exposure time for each it will make a good summertime project that could last into September.

Despite the ever-present smoke I was able to collect the data for subframe 1 which includes most of the East Veil (NGC 6992) and the Network Nebula (NGC 6995): left click the image below, then right click the enlarged image and choose "Open Image in New Tab" to see the image at 1/2 scale:

 

 

For fun, here's a try at a starless version using StarNet2 in PixInsight:

 

This is LRGB with all exposures 120s, L = 20 lights, R = 11, G = 12, and B = 12.

I think I dark-clipped this a little in my processing haste, but it will get another processing eventually.  Here it is tucked into its place in the eventual mosaic:

 

6995 is in the overlap area between subframes 1 and 3. The next target will be subframe 3 to complete the Eastern Veil and give me some practice using PixInsight to create a mosaic.

Some other tidbits from this too-rare night of imaging:

• The QHY-5II guide scope was flawless with over two hours of guiding without a single disconnect. It really does need USB3, it seems. 
• Not only that, but tracking errors were limited to 2 frames in 58. A rate of 1 bad frame in 29 is a lot better than the 1 in 6 that I had experienced earlier this year.
  
• NINA's Advanced Sequencer finished subframe 1 and started subframe 3 imaging without any attention on my part. This was the first time I had tried this. I wasn't willing to do another two to 3 hours of imaging so I reluctantly shut it down at that point.
• More NINA: Its mosaic feature is nicely integrated into the Framing Assistant and sets up the Advanced Sequencer for all the subframes with simplicity.
• Even More NINA: If you want to use the Framing Assistant with images while you're someplace without Internet, go to the NINA download page and grab the Offline Sky Map Cache file (2 GB) It replaces the existing cache folder AppData >  Local > NINA > Framing Assistant Cache. Don't forget to change the Framing Assistant Screen's Image Source setting to Offline Sky Map! Incidentally, installing this allows you to zoom out and use Framing Assistant like a (rather strange) planetarium.
• I seem to have gotten the hang of PI Deconvolution. I don't know why it was so temperamental before, but the key seems to be in the Deringing settings. A Global dark of 0.03 to 0.02 seems to work well, with Global bright typically between zero and 1/2 of Global dark.
  

 

Smoke and the June New Moon; A Couple of Things Fixed (maybe)

This week would be a prime time for heading out to Lac qui Parle state park for some dark sky imaging. But there's some serious smoke action ruining that plan. Here's what the smoke looks like from space.

The location of Lac qui Parle State Park is given by the red dot

Fortunately for the health of people in the Dakotas and western Minnesota it's all far above the ground and the air we breathe. 

This is a blue light satellite image from late in the day of 12 June. Both Dakotas are under multiple smoke decks; you can see the layering across western Minnesota where each layer casts a shadow onto the layer beneath it. The eastern edge of the smoke is slowly pushing eastward. 

 I can't say I'm confident this will clear out during the coming new moon weekend of 16-18 June. Western Canada continues to burn.

It's already complicated trying to forecast clouds and adding smoke makes it all the more difficult. Clear or cloudy? Transparent or murky? The decision to travel an hour or more to a dark sky location has become an exercise in nowcasting.

In some ways this is much the same as a cloud deck. It may not be opaque, but the extinction is formidable. In the image below of north central south dakota you can see contrails at flight level casting shadows onto the smoke!

---------------

Two issues may have been resolved last night. The glitchy behavior of my QHY5LII guide camera was absent with the USB cable connected to a USB3 port, and I got a beautiful PHD2 calibration after I turned off the mount's PEC. This has not been a problem in the past, so I wonder if the PEC file become corrupt while it sat unused this winter. It's going to stay off until I have a chance to retrain the mount.

---------------

I've also learned how to use NINA to acquire images for mosaics, and have set up a file to perform a six-panel mosaic of the Veil Nebula. The first two panels will complete the East Veil.

Smoke and the Nebraska Star Party

I registered and had purchased a park sticker. A few days before my planned departure to the Nebraska Star Party I assessed the smoke situation and decided not to attend. My personal judgement was that it wasn't worth the travel expense and hours of driving to seek out what would probably be mediocre sky.

Last night I was at a friend's house north of Minneapolis and the effect of the smoke was obvious. The limiting magnitude was around 4 instead of the usual 5.5. Extinction due to smoke was costing us somewhere around 1.5 magnitudes.  That translates as requiring exposure times to be 4 times their normal values.  

Looking at satellite loops suggests the smoke blanketed NSP the first three nights (Sunday, Monday and Tuesday nights). Wednesday night was probably the best of the event, but even then there were occasional clouds combined with smoke. Thursday night's forecast is for fewer clouds but more smoke. 

Considering the five nights from Sunday through Thursday, recent years have not been kind to NSP. In 2019 it rained four of those nights. If NSP 2020 had taken place it would have provided maybe five hours of good quality imaging, unfortunately coming as three hours one night and two another. This year's NSP 2021 may have been a complete loss for imaging unless you're willing to image through smoke.

I'm beginning to think I was spoiled by my first three NSP trips (2014, 15, and 16).

The question is if this is just a bad run of weather or an indication of some sort of "new normal" as the climate warms and wildfires become a regular feature of summer.

Time will tell. And while we wait, get fully vaccinated if you aren't already!

Forest Fires, Smoke, and Transparency

Forest fires are raging in the northwestern U.S. and western Canada, taking lives and resulting in the destruction of property. There are a lot of fires:

Active fires on 8/31/15. Map from http://activefiremaps.fs.fed.us/

The effects are not limited to the areas of burning. Smoke is being carried hundreds of miles eastward, leading to occasional serious decreases in air quality that can affect those with respiratory illness.

Another far less serious effect is the greatly diminished transparency of the sky. During the day the sky is a yellow-brown veil and at night dimmer stars are extinguished and the moon starts to look like it's in eclipse:

The full moon at an altitude of 34 degrees. It should be colorless, not yellow!

Most observing and imaging activities are put on hold until either the fires end or the winds shift. This degree of transparency loss has happened before, earlier this year and once last year. Prior to that I think one must go back about seven years or so to see a similar event.