Another Imagining Year Ends; Solar Panel Recharging of Batteries.

Bye-bye, 2019

Winter has fallen onto the region with a loud thud. Snow depth is now seven inches and the temperatures are near normal (for the next week, anyway). For a warm weather person like myself this essentially means outdoor astronomy is in hibernation until spring.

It remains possible that I may use the imaging platform at Cherry Grove, but I can't say I'm in the mood for that at the moment. So let's see what else there is to do.

I have some mirrors that are in polishing/figuring stage, so I could get back into those.

There's always the task of learning image processing software, but if things continue on like they have the last two years with awful weather there's no rush.

I could do some programming and try to quantify the meteor reflection data I collected a couple of years ago. But instead, let's have...

More Power Fun!

One thing that intrigues me is solar power for recharging batteries at remote sites. A few years ago when I priced this out solar panels were too expensive compared to buying batteries. But with the continuing decline in panel prices it's time to reassess.

The first step is to determine my power needs. This is the product of my imaging setup's power requirement and the number of hours spent imaging in a typical evening. The first is something I've measured; my current setup (mount, laptop already charged, dew heaters set higher than usual at 50%, CCD with cooling at 70%, autoguide camera) setup draws about 3A. That means I can image with about 40W of power.

Next we need to know how many hours this power will be needed in an evening of imaging. Let's consider the cases of an equinox and summer solstice at 45N latitude, and for each imaging through either nautical, astronomical twilight, or full darkness.

Summer solstice: full dark 3:20, astronomical twilight and darker, 5:31; nautical twilight and darker, 7:10; civil twilight and darker, 8:25; sunlight, 15:35.

Equinox: full dark, 8:31; astronomical twilight and darker, 9:42; nautical twilight and darker, 10:57; civil twilight and darker, 11:50; sunlight, 12:11.

Let's say you image during astronomical darkness and start up about a half an hour before that for polar aligning, target acquisition, and letting things settle. Depending on the time during the summer you will be using power for about 6 hours (solstice) or 10 hours (equinox).

Multiply the above hours by 3 amps and you get 18Ah (solstice) or 30Ah (equinox). These are what you need to put back into the battery after an all night imaging session. (In terms of energy in watt hours, these are about 216 and 360 watt hours.


[Digression: My primary battery is 50Ah. Draining that by 18Ah is only 36%; a 30Ah draining is 60%. By August 1 this has changed to a drain of 22Ah or a 44% drain.]

At this point it's tempting to say a 100W solar panel can bring a battery back up to full charge in only a few hours. Can it? There are a few wrinkles to consider that can reduce that 100W:

• Clouds: Cirrus are no problem, but typical fair weather cumulus can drip power by anywhere from 8 to 20% [ref]. Total overcast drops power by 50 to 75%.
• Heat: Higher temperatures are doubly bad. Panels become less efficient as the temperature rises, and AGM batteries are better off being charged at lower voltage. For typical NE afternoon temperatures (37C or 95F) this leads to a panel efficiency drop of about 2.5% and an increase of about 6% in battery charging time.
• Resistance losses can be minimized by using wires that are heavy enough for their lengths. In my possible system this means using 12AGW throughout and keeping the runs reasonably short, and should not be a factor.
• Charge controller efficiency. MPPT controllers generally have an efficiency in the area of 95%.
• Panel orientation isn't a big factor so long as you can keep the panel face reasonably perpendicular to the sun. This means turning it hourly and using some kind of adjustable altitude brace.

In the worst case it's a hot, overcast day (which are rather mutually exclusive) and we multiply 100W times 0.5 for overcast x (0.975x0.94) for a 95F day x 1.0 for resistance loss (none) x 0.95 for controller loss x 0.86 for being 30 degrees off perpendicular all day. In other words, that 100W becomes 37W. 37W times total daylight time minus two hours is about 500 watt hours (solstice) or 370 (equinox).

Conclusion: Even in an unlikely worst-case situation a 100W panel + MPPT controller should be able to do nightly recharges adequate for imaging using my setup.

Back From the 2019 Nebraska Star Party

I was at the 2019 Nebraska Star Party for Sunday through Thursday nights and it could have gone better.

It's been a wet year in Nebraska and that means the usual mosquito herd is larger than normal. The first night, Sunday, there was only a modest breeze that faded around sunset; the herd emerged and immediately zeroed in on me. My bug spray was unable to hold them off and I was forced to retreat to a screened enclosure after obtaining only a polar alignment. No imaging.

Monday night had a partly cloudy hour, but Tuesday through Thursday Nights were all cloudy with episodes of rain. So for me NSP 2019 was a bust. At best I would have gotten one solid night had I been able to endure the biting.

I have a feeling that as the trend of increasing rainfall continues (thank you, global warming) this will be the case more and more often. That means it's time to adapt.

My thought is that if I can work from a screened enclosure I can manage even on those really buggy nights. This means I need an enclosure and a way to control my imaging rig from a distance of maybe 20 feet or so.

At present I control everything using a single USB cable from laptop to imaging rig. According to standards this limits me to about 16 feet between laptop and rig. Subtracting 6 feet for drops to and from the ground and I'm left with about 10 horizontal feet of separation, so I need to extend my USB. This can be done using powered USB repeaters, but that would mean added connections and power lines. the simpler way is to use an Ethernet extender like this:

This passes USB between two boxes via up to 60m of Cat5 or Cat6 Ethernet cable, with only the box on the rig requiring external power. Some serendipity: The required power is 12V DC and uses the same connector I'm already using with my USB hub on the rig. And the on-rig box acts as a powered four-port USB hub. The only drawback is that this is strictly USB 2, so if I add a USB 3 device I'm in trouble. This is available on Amazon for under US$60.

Focusing is not pleasant when you're being bitten, so a motorized focuser is needed. Unfortunately the only motorized focusers for an AT-65EDQ cost close to $1000 when all is said and done. This is a very nice little scope, but I'm not sure I want to spend that kind of money on it. A much less pricey option is a JMI Motofocus, but they have stopped making them for the AT65 and I could find no vendor who has one in stock.

Luckily some years ago I was given an Orion version of the Motofocus. It wasn't designed for the AT-65, but it was close. All I needed to do was add a small piece of aluminum sheet to it and buy a couple of longer bolts.  I made a nice long phone cord so that it can be used over a much greater distance than the coiled handset cord it came with.

The piece of aluminum (silver rectangle in the above image) is epoxied to the Orion-provided mounting bracket to extend it the required distance. The longer screws and small stacks of washers provide the needed offset to keep things square and allow the larger focus knob to rotate freely. Note that there is no clutch on this so while the motor is attached there is no manual focusing. If you need manual, just undo the two outermost screws on the bracket and replace the motor with the AT65's fine focus knob.

The last operation is one I can't really do much about: polar aligning. This will still require standing at the scope and adjusting azimuth and altitude by hand. Nothing is perfect :)


The final adaptation is a freestanding screened area that's large enough for setting up a small table and chair. I went with this one from Coleman:

This is available from multiple vendors for a wide range of prices. The footprint is a spacious 10'x10', so I'll even have room for a little lie-down while imaging. Despite this being floorless, it gets good comments about keeping the bugs out. We shall see. One thing, though--don't imagine that this is adequate as a sun or rain shelter. I purchased mine from Kohls.

So I'm now set for the mosquitoes. Unfortunately there's nothing I can do about clouds and rain, but that's always been the case.

DIY Sky Brightness Meter; Coleman Outdoor Compact Table; Lapdome; First light with Losmandy G11G

I've been tinkering with a microprocessor called an Elegoo Uno processor, and as a part of that I came across something called Phidgets. This is a collection of clever sensors and devices that can be controlled by laptops and mobile devices.

One of the sensors is a light detector. It's capable of measuring light down to 188 microlux, which just happens to match the value you would expect to measure for a nearly perfect dark sky site. That suggests it might be the basis for a night sky brightness measuring device. Fortunately it's built to report visual brightness and not full spectrum which can include a strong IR component.  The Phidget sensor is made up of two sensors; the second is IR and is used to correct the first.

The actual semiconductor sensors sits in a well with beveled sides within a plastic case. Rather than expose this to stray light I placed it in a PVC tube as shown in the picture and diagram below. This shield tube is probably too long, which means I'm blocking out some of the light cone entering the sensor compared to what it was normalized to receive.

Version 1: Long light shield

Version 1: Long Light shield

The length of the version 1 light shield was based on an incorrect calculation. Correcting the error gave a light shield length of 60mm, or about half of the Version 1 length. A few minutes of sawing gets us to Version 2, which is decidedly smaller in appearance:

Version 2 closed

Version 2 open

At this reduced length the shield is not much more than a way to keep the two caps together. In fact, it doesn't act as a shield at all; it's completely outside of the sensor's field of vision.

There are two black objects on top of Version 2. The smaller one is a combination temperature and humidity sensor; the larger is the hub used to communicate with my laptop via USB. The USB connection provides the power needed by the devices.

Thus far only Version 1 has been tested.The conditions were clear sky with a first quarter moon. (The sensor was pointed straight up and did not include the Moon in its field of view.) The reported light value was 2 millilux or about 2000 microlux. Is this a reasonable value?

It now gets a little complicated. First we need to correct for the oversized light shield. This introduces a factor of about 1.67 (a very uncertain value determined from indoor testing) so the measurement is now about 3330 microlux.

The site I was testing at was not Bortle 1, so the natural sky contributed some signal.  Assuming the site was at midpoint of Bortle 4, it was at about 520 microlux.

Next we have to add on the contribution of the first quarter moon, which takes a site from Bortle 1 to Bortle 5. A Bortle 5 sky at m = 19.7 has a value of about 1560 microlux, so the moon adds about 1370 microlux

In other words the sky starts at 520, to which we add 1370 from the moon for a total of about 1900 microlux.

Is 1900 close enough to 3340 to call it worth working on further? Yes, definitely, given the uncertainties in the numbers. If it had blown up or started a fire I'd say that it should be set aside, but this did neither.

I will continue to tinker with it, including rewriting the sample polling program to take time averages and log them. In addition to more local testing I'll also take this to this year's Nebraska Star Party, where the sky is Bortle 1 😃

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New Stuff:

1) My old field table finally fell apart after 15 years of service and has been replaced with a Coleman Outdoor Compact Table.

It seems sturdy enough and I like the solidity of the aluminum tabletop, but time will tell how well it holds up. So far the only negative I can say about it is the carrying bag; it's several times larger than it needs to be and allows the contents to flop around inside.

2) You know how when you try to make something you get the feeling that it's just not coming together and that you might be wasting your time? That sums up my attempt to make a portable light box for my laptop. I have thrown in the towel and puchased a LapDome. I haven't used this in the field yet, but it looks like it should be a great way to keep laptop light from interfering with visual observers without make the laptop difficult to use.

It seems really well made and should help with dew control, too. I kind of wish that it had side openings for cables in addition to the rear opening; my laptop has only side ports and none at the back.

One improvement I may make is to cut a board to fit the inside bottom to keep the laptop's air intakes happy.

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Lastly, the same night I was tinkering with the light sensor and watching people try to get first light with the Cherry Grove Observatory Planewave 12.5" CDK I also got some time with my new mount. It worked great! The following image is little more than a simple trial: 14x60s luminance frames and 15 dark frames. First, the full frame, reduced in size. Click to see it at 31% of the original scale:

Obviously an AT-65EDQ doesn't give the best pixel scale for an object like M51.

Here is a crop to the target so you can see it a little better. Click the image to see it full scale.

Not bad for total exposure time of 14 minutes! (Camera = SBIG ST-8300M)

Luminance is nice, but I can't wait to try out the other three Astrodon filters.😀

Getting to Know My Losmandy G11G

Yes, it's still winter, but eventually it will be time to resume imaging. I've got a new mount to use and I hope to return to imaging with my good old SBIG ST-8300M. The new wrinkle for this year is integrating all the software and hardware.

This morning I ran a little practice session to see if I had everything down for getting it all running together:

• StellariumScope for managing USB
• Stellarium for target acquisition
• PHD2 for autoguiding with a QHY5L-IIM
• PoleMaster for polar alignment
• ImagesPlus Camera Control for managing the SBIG
• ASCOM for controlling the mount

Amazingly the mount seemed to point in the right direction and all the software behaved itself. The QHY5L was happy with the powered USB hub, too. Who knows, maybe when I get out under the stars I'll even get AstroTortilla to work.

Tidbits learned along the way

• Some people say that the Ethernet cable you need to use for connecting a laptop and the Gemini2 controller can be an ordinary straight-through cable if you have a recent laptop. Well, maybe and maybe not. My Dell laptop is only a year old but it definitely needs a crossover cable.
• When running from laptop you can leave the Gemini hand control disconnected. This will save you a little power in the field.
• One 35Ah 12V battery can run an entire imaging system, or at least mine.  That includes laptop, SBIG ST-8300m with cooling running at about 60%, dew straps, guider and mount. No low voltage problems, at least with a freshly charged battery. I think the battery can probably keep it all running for an entire summer night before needing to be recharged.

Another item from the 2018 Nebraska Star Party

As an imager I'm supposed to despise green laser pointers, but we all know they can come in handy. A vendor was selling a nice one at NSP and I picked it up for occasional use.

The handle is made from white birch. This pointer is powered by 2 AAA batteries instead of tiny button batteries. If you want one for yourself, contact Brian Basiaga.

Yay for me!

This is blog post number 200! Next up is an entry about a nifty Photoshop plugin that can be used to enhance an image's dynamic range.

Remote Control Range

Here's my first report from the 2018 Nebraska Star Party. I realize it's now 2019, but better late than never, right?

In an earlier post I talked about exploring the ability to remote-control my imaging using a wireless router (the ASUS RT-N12) and Android tablet running TeamViewer. The theoretical range of this setup was 500m, and I posted a diagram showing a 250m radius around the anticipated imaging site:

This assumed I was going to set up on north end of the low hill north of the dinner shelter. I ended up imagining from a position further north (the blue dot in the diagram below):

The green dot is the location of the dinner shelter, from which one could see the setup point on the horizon. The signal there was strong enough to allow control of the imaging laptop. This is about 380m from the router. I did a little more exploring and found that at the yellow points there was good enough reception to be able to see the laptop display but not control it. The red dots indicate where the signal caused TeamViewer to give up.

I think it's fair to say if one can maintain a line-of-sight contact with the router the range of 500m is a fair estimate.

Happy New Year!

It's been a long time since the last post, mostly because I haven't had much to write about: Let's get right to the excuses:

• It was a terrible year for weather; it seemed as if every imaging opportunity was clouded out
• My transition to computerized imaging that started the winter of 2017-2018 kind of slowed me down
• There was the mini-fiasco of the very late arriving Planewave 12.5" scope for the imaging platform. It didn't arrive until after the Nebraska Star Party and didn't get onto the mount until late August. Basically the delay pushed the timeline back about 6 months
• Unlike a lot of years, this year winter arrived early (November 1) and stayed. There was no pleasant, gradually cooling autumn to image through

So, now that that's out of the way, we can get on to catching up. After such a dismal year what could a person do other than double down on what seems at times to be a frustrating hobby? That's right: I am upgrading things.

A) MOUNT

The old CGEM mount is out, replaced by a Losmandy G11G. In the pantheon of mounts, the CGEM is somewhere around "tier three." The best "lightweight" mounts are made by Astro-Physics (Mach 1GTO) and Software Bisque (MyT).  Both of these price in around six to eight thousand dollars when you add the usual bells and whistles. The G11G doesn't quite deliver the superb performance of these two "tier one" mounts, so I'll call it "tier 2," and it's about $4500 fully loaded. I went for the Gemini II version (that's the second 'G' in G-11G) even though it's not necessary for imaging--it's just nice to have in case I decide to return to visual astronomy.

The G-11G is a major upgrade from the CGEM. Let us count some of the ways:

1. It's solid. Push on the GGEM head and it wiggles a little, whereas the G11G doesn't budge. There is simply no play in it
2. I expect it will track far better than the CGEM. My CGEM had substantial periodic error that I could never really get rid of. The G11G will probably be an order of magnitude better
3. It can connect to my laptop by way of an Ethernet cable, not a funky USB-to-RS 232-to-hand control cable.
4. It's lighter than the CGEM. The head weighs over 10 pounds less and disassembles into two pieces to become even more portable. On the minus side, the field tripod is large and heavy compared to the CGEM's tripod.
5. Its carrying capacity is far greater than the CGEM's. There's no telescope I own or am ever likely to own that will push the G11G to anywhere near its capacity
6. There are more differences, but until I can actually begin using it (2018 crumby weather, see above) I'll not comment on them

B) FILTERS

I'm not going to say that my Baader filters are inadequate, but it's become clear that they do have internal reflection issues. And in the case of the narrowband filters their 7nm bandwidth is not as good at rejecting sky brightness as narrower filters.  So out they go to be replaced by Astrodons. I plan to purchase new LRGB filters. The H-alpha filter is a needed upgrade; but over the years I've hardly used my S-II narrowband filter, so that won't be replaced. I may not even replace the O-III filter. The size filters to get will depend on part (C)...

C) CAMERA

As I write this, my thought is to continue using my SBIG ST-8300. It will be interesting to see if it still functions after a few years of rest! If I stay with it the above filters would all be the 36mm round unmounted type.

This is kind of wide open-I have the option of upgrading my ST-8300 to an STF-8300 or maybe jumping to CMOS. Cooled CMOS monochrome is an intriguing technology, but I kind of feel it isn't quite mature enough yet. If I go that way or get a different CCD it's possible I'll be able to use 31mm filters and save a little money. I have some research to do!

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I made a rare appearance at last night's monthly club meeting. I was there for two reasons-to take part in the pre-meeting meeting of the Cherry Grove Observatory committee, and to pick up some swag.  I did most of the graphics designs for the ALCON 2018 national meeting and had asked for payment in the form of some items my designs appeared on. One of the club officers was kind enough to bring some to the meeting for me.

I mention this because the planned guest speaker was unable to appear at the meeting and was replaced by a video presentation about climate and climate change. I admit at first I was skeptical of what the presenter's agenda was, but it turned out to be excellent.

The speaker, Dan Britt, is a physical geologist who has studied climate change on geological time scales. While he's rather circumspect about stating his conclusions, he clearly lays out the geological evidence that illustrates how anthropogenic carbon dioxide forcing is the driving force (by far) in contemporary climate change; surface temperature is increasing and the seas are rising in his view.

This is a presentation for a non-technical audience, so don't expect to be challenged by esoteric details of the science involved. But what he says is in perfect accord with my understanding of the science.

Highly recommended: https://www.youtube.com/watch?v=xgNxF2HlN3w