Own a Celestron GEM? Don't Leave Home Without This!

There are any number of minor unanticipated events that can ruin a night of imaging at a remote site.

1. The weather can go bad. A sheet of clouds can roll in seemingly out of nowhere and obscure the sky. The wind can make your scope bounce. A heavy dew or frost can overwhelm your dew prevention gear.
2. You can forget to bring a critical component. Over the years I've managed to forget counterweights, the counterweight shaft, cables, the dew shield for an SCT, and probably more things than I can remember that I forgot.
3. Something can break in a way that simple tools and duct tape can't fix.

It was fault number 3 for me last night. Rather than going through power-up initialization my CGEM's hand control would stop with the display frozen on "Transmitting data..." Cycling the power was ineffective. Switching from AC to DC battery power didn't help. The evening was over before it started. This wasn't so bad at a site only an hour or so from home, but imagine it happening after driving eight hours to the Nebraska Star Party.

What I didn't know at that point was if it was the mount or the hand control that was the problem. Possibly both. Having Celestron fix the mount would probably run well over the $700 I paid in 2010. That's a sizeable portion of the cost of a new Losmandy G-11, a mount that would be a better than good replacement. On the drive home I had a bit over an hour in which to consider all the mounts that might replace my CGEM, and none of them were what I would call inexpensive. Certainly a new mount is not in my budget.

A new hand control would be more acceptable at about $100. Or I could take a substantial risk and go cheap by picking up a used control on ebay for less than $40.

With some trepidation I went online and found that "Transmitting data..." message meant the hand control had lost its firmware and was waiting for a refresh. A simple reinstall of the firmware might fix the issue.

The hand control comes with a cable that to connects its base to a computer through a serial port. As you're probably aware, serial ports are essentially extinct; very few computers still provide them. The workaround is a serial to USB cable called the TRENDnet TU-S9:

TRENDnet TU-S9 (USB 1.1 version)

I have the older model shown above that I used a few years ago to update the control and the CGEM motor firmware. It works fine with Windows Vista and 7. A newer model is white, sells for about $10 on Amazon, and is said to be compatible with Windows XP through 10 and OS X 10.4-10.11. All you need to do to restore the hand control firmware is follow the instructions found in this excellent YouTube video. It takes all of five minutes, and in that amount of time I had my mount back in working condition. My budget was safe!

If I'd had it with me last night, I could have fixed my mount and taken advantage of a beautiful evening.

The moral of this story: If you have a Celestron mount and you're traveling to a dark sky site, avoid a wasted trip. Be sure to bring the cables you need to reinstall the firmware, and if you've got a laptop put the installer on it and a copy of the appropriate firmware version(s) for your mount(s). You can bet I'll be bringing this to Nebraska this year.

A New Astronomical League Bright Nebula Program Object List: Getting Better, but Not Good Quite Yet

Finally! A New version of the AL Bright Nebula Program list.

IN BRIEF

• It's brighter--all the dimmest objects are gone
• It's clearer--most of the seemingly conflicting objects are gone
• It's buggy--there are a lot of duplicate items and typos, and a few head-scratchers remain

IN DETAIL

After almost two years of letting the Astronomical League's Bright Nebula Program suffer with an object list that was confusing and somewhat buggy, a new version is out. While the new list has some improvements, it continues the legacy of errors found in early versions.

Errors that should have been caught include:

• Six objects are on the list twice
• There remains one object on the list that is known to be a catalog error. (Is this intentional?)
• One object's existence is disputed (NGC 1990: is it a reflection nebula or simply glare?)
• Some designations are simply wrong. Examples include: Pickering's Triangular Wisp is given an NGC number that belongs to a galaxy; apparent typing errors assign incorrect catalog numbers to the western branch of the Veil, Struve's, Running Man, Eta Carinae and Barnard's Loop nebulae
• Unlike earlier versions that were ordered by RA, the new list appears to have been left in random order
• Two entries are given the same index number of 116

It's as if the list was never reviewed or proofread. It's definitely not up to the AL standards to which I've grown accustomed.

One upshot of the errors is that there are actually only 143 or 144 objects (depending on whether the disputed object is retained) in a list that is claimed to have 150 objects.

Despite its smaller size, the new form of the program is much easier to complete. Gone are the objects in Lynds brightness categories 5 and 6. Most of the 4s have been dropped, too. There are also fewer objects so far south that they're unavailable to northern observers/imagers. The loss of objects is countered with a lot of new reflection nebulae; these won't be all that easy to image from urban locations, but my guess is that they're not as difficult as imaging Lynds brightness 5 and 6 objects.

Other improvements long overdue are the resolution of some of the problematic designations like NGC 6526. The confusing object assignments for the Cat's Paw, Gamma Cass, Heart, Butterfly, and Pelican nebulae areas have been dealt with. There's still an issue with the Seagull, but progress has been made.

The list difficulty is so different now it will be interesting to see if the award numbering system is reinitialized. On a related note, the certificate number I have on paper continues to be different from the one the AL reports on its web page. I doubt it will ever be fixed.

One final comment: It would have been nice if the program coordinator had thanked those of us who completed the old form of the program and essentially acted as beta testers.

I'm currently working on a corrected object list that will be in PDF and spreadsheet formats. I'll post a download link here as soon as it's ready.

Sharing the Back Yard

I live in a second-tier suburb south of Minneapolis. About a mile away is the Minnesota River valley, a broad expanse that's been kept relatively undeveloped. One might expect to get a lot of wild visitors from the valley, but seldom has anything out of the ordinary been observed. Aside from deer that have been seen only two or three times in over 30 years, it's the usual suburban mix: Owls, rabbits, and raccoons (although their numbers seem to be greatly reduced in the last 20 years or so).

Increasingly present are species that are reclaiming old territories. Bald eagles have become frequent visitors. There's a giant old cottonwood tree in an adjacent lot that someday could play host to a nest, but it might be too far from the river. "Location, location, location," applies in the animal world, too.

Coyotes are also returning. I've heard them howling nightly at most star parties in the open country but now they're back in the suburbs. I've gotten a few glimpses of one trotting quickly away in the last few years, and this spring I've seen one that seems more at ease. Twice it's been seen sleeping on the back yard lawn at the sky brightens at the end of dawn:

The gleam in its eyes is from the flash, not radioactive waste! This one seems more at ease with its surroundings; It showed only mild interest in people walking a few hundred feet away.

Looking perfectly at home

Starting the morning commute

There's no shortage of food available to it. All sorts of rodents are on the menu: Rabbits, squirrels, and shrews are in abundance this year. Add to that all the pet cats and small dogs that are allowed to roam outdoors and I doubt the coyote will go hungry. (Our cat is an indoor cat.)

Bobcats have also been sighted in the river valley and I'm really not eager to see one in my back yard. I consider them much more likely than a coyote to go after larger prey like an imager.

The Minnesota river feeds into the Mississippi river a few miles downstream from here, and together they form a natural impediment to animals traveling southward. Black bears, not all that uncommon in the northern areas of the Twin Cities do occasionally make the trek southward. Two years ago a black bear made it "south of the river" and roamed for a few days through this area. Only the wayward bear came to harm; it was shot in the leg by a police officer and may have survived to return north.

Virgo Cluster Mosaic Ib: A Less Aggressive Approach

Last time I settled on using a 200mm lens to make a mosaic of the entire--fifteen degree square--Virgo Cluster. This would require something on the order of 15 to 24 subimages.

A club member pointed out that the galaxies probably wouldn't look very good at that scale, and he was right. Here's a simulation of 200mm vs. 700mm.

700mm image

200mm simulation

The galaxies are starting to lose their distinction from stars, pretty much ruining the point of a galaxy cluster mosaic.

His solution is to image only the core of the cluster, an area of about 8° by 5°. That's roughly 1/5 of the entire cluster's expanse, but it does contain the densest concentration of galaxies of interest to visual observers.

I'm going to repeat the calculations from Part I for the AT65 telescope. N = 3.5 (round up to 4) and M = 3.25 (round up to 4). So this can be done with about 16 images using much better optics.

I had some time to put together the layout of the 16 frames:

Virgo Cluster mosaic layout. Blue box, suggested area to be imaged; green markers, centers of subframes; red marker, center of mosaic; red box, area of mosaic.

The final mosaic will have a pixel counts that are about three times the frame dimensions. Since I'll be using a Canon T2i, that will give a 162 megapixel mosaic!

Virgo Cluster Mosaic I: Choosing a focal length

The galaxy imaging I did this spring was so much fun that I'm considering a big project: A mosaic of the Virgo Cluster. One of  the club's members suggested that such a project could result in a poster that would be suitable for fund raising at the 2018 Astronomical League Convention (which the club is hosting). I don't know anything about poster printing and marketing, so I'll leave that to others.

The mosaic, on the other hand, interests me.

My images were all taken using my TV-102; with the 0.8X FF/FR it has a focal length of 700mm and a field of view using an APS-C DSLR of about 1.3° by 1.1°. That's too small a field to make this practical--The Cluster has a size of about 15° by 15°, which is an area about 140 times the TV-102 field. When overlapping is considered it gets even more impractical. I would like to finish this within my lifetime!

Another option is my AT65 (422mm FL) with a field that's 3° by 2°. This means I'd need 38 images not counting the area lost to overlap needed for proper alignment. This is better, but still quite a task, and nearly impossible given the fickle weather around here.

How about a 200mm lens? Its field is 5.1° by 3.9° and gives about 12 images needed before overlap is figured in. That's not bad. A big galaxy like M84 manages to be about 85x74 pixels, also acceptable. It's time to pin down the cost of overlapping.

Consider a single line made of identical overlapping images. We take W as the image width and A as the overlap between one image and the next.

The width of sky covered by the first image in the line is W. Each additional image in the line adds (W - A) to the line length, making it easy to write an expression for the total line width W:

W =W + (N-1)(W-A)

We can solve this for N:

N = (W - W)/(W-A) + 1

Pretty simple, huh? We can do the same for height, letting M equal the number of images of height H in a column, B be the overlap distance, and H the total height of the column.

M = (H - H)/(H-B) + 1

We can fiddle with this a little more to express the overlap as f, the fraction it is of the width or height. This is useful because we'll almost certainly try to use the same fractional overlap in both directions.

f = A / W = B / H

N = (W - W)/[W(1-f)] + 1
M = (H - H)/[H(1-f)] + 1

One more change, let's define the constant F equal to 1/(1-f), giving
N = F(W/W - 1) + 1
M = F(H/H - 1) + 1

Notice that the right hand side of these expressions doesn't necessarily guarantee that N and M are whole numbers. It's up to us to round them up or down to an integer value depending on how well the resulting grid of subframes covers the target area.

One more alteration improves the convenience:

N = F(W/W - 1) + 1
M = F(H/H - 1) + 1

We should check this pair of equations for correct behavior in the case of no overlap. In that case f = 0 is zero and F = 1. This gives 

N = (W/W - 1 + 1 = W/W
M = (H/H - 1 + 1 = H/H

The number of subframes, N times M, is equal to (WH) / (WH), the area of the mosaic divided by the area of a subframe. This is exactly right in the limit that the subframe is much smaller than the mosaic and we can ignore the need for N and M to be whole numbers.

For the 200mm lens, we have (expressing everything in degrees) W = 5.1 and H = 3.9. For the Virgo Cluster both H and W are 15, so

N = F(1.94) + 1
M = F(2.84) + 1

Let's assume a 1/3 overlap rule, so F = 1 / (1 - 0.333) = 1.5.  This gives us

N = 1.5(1.94) + 1 =  3.91 (round up to 4)
M = 1.5(2.84) + 1 = 5.26 (round up to 6)

So--as a first guess--24 images are needed to make a rectangular mosaic of the Virgo Cluster.This could be as few as 15 (3x5), 18 (3x6), or 20 (4x5) depending on the fit and composition considerations. I'll leave that for Part II.

How about a 135mm lens that gives a 9.5° by 6.3° field?

N = 1.5(0.58) + 1 =   1.87 (round up to 2)
M = 1.5(1.38) + 1 =   4.47 (round up to 5)

Only 10 images, but the galaxies would be awfully small.

And for my AT65, with a a 3.0° by 2.0° field?

N = 1.5(4.0) + 1 =   7
M = 1.5(6.5) + 1 =   10.75 (round up to 11)

77 images, a bit much for my taste, and really difficult to get done by ALCON 2018.

Just for fun, let's do the case for the TV-102.

N = 1.5(0.58) + 1 =   16.8 (round up to 17)
M = 1.5(2.38) + 1 =   19.95 (round up to 20)

That's a mosaic with 340 subimages. That's not going to happen.

Markarian's Chain

The Minnesota Astronomical Society (MAS) has sponsored Messier Marathons for many years. Recently they've begun holding the marathon twice a year by adding a fall gathering for what's called the mini-marathon.

The spring marathon gives everyone a long, good look at the Virgo cluster of galaxies, home to 16 Messier Objects. There are more than just Messier galaxies in the cluster and deciding which particular faint fuzzy you see in your eyepiece can be difficult. Navigating the Virgo cluster is difficult for anyone who hasn't done it frequently.

Beginners wander into the cluster not just during marathons but also when working on their Messier lists. It's not unusual for them to leave the cluster with a sense of frustration.

With that frustration in mind the MAS started what it calls the Virgo Venture, a spring evening during which all attention is on the cluster and learning how to navigate it. Special star-hopping charts are provided and there's an experienced navigator around to help observers find their way.

It was at one of these Ventures that I first observed Markarian's Chain, a gentle arc of galaxies in a small patch of sky. It was the first time that I'd seen more than two galaxies in the same field of view. In fact, I could count six, and with a little travel add a few more! I was impressed, and it marked a first appreciation of wide field viewing for me.

This year's Venture was held last Saturday despite thinning cirrus clouds running east-west over the site and a thick plume of smoke from Canadian wildfires. My imaging target was the Chain but given the overhead murk I didn't have a lot of hope. I shot an hour of light frames with the haze and another hour as the haze was disappearing, so it didn't turn out too badly.

The entire group of galaxies fits tightly in the 700mm view of a TV-102 with its focal reducer/flattener in place:

Markarian's Chain, stretching from the two fuzzies in the upper left corner to M84 near the right edge.

The acquisition details are at AstroBin. Briefly this is two hours of light frames using a modified Canon T2i at ISO 800, a TV-102 at f/7, and autoguiding.

The weather forecast suggests a week of clouds and then the moon comes back. A good cycle to do some lunar/planetary imaging, I suppose. June's new moon will bring a last shot at many Arp galaxies, and then it's summer and back to nebulae!

M81 and 82 Revisited

A nice clear night and an opportunity to image from a friend's home north of the city lights produces a pretty picture:

 

This is based on 44 x 3m light frames with 15 dark frames, Canon T2i at ISO 800 on a TV-102 at f/7.

Power saving update: the software I talked about that turned off the laptop LCD display wouldn't keep it off. Apparently something about using ImagePlus kept turning the display back on. This wouldn't be a problem if a hand control was used to run the DSLR and images were stored on-camera.

Battery Update: I ran the laptop (fully charged), dew prevention, mount and camera from the 35Ah battery for four hours; loaded voltage fell from 12.7 (unloaded, 13V)  to 11.8V. Unfortunately I popped the battery onto the charger as soon as I got home and didn't check its final unloaded voltage.

Assuming it was 12.1V it would have been at 50% capacity, meaning it would have supplied about 17Ah or about 4Ah per hour. This is about right if I take into account that the old laptop battery was in place and it could run the laptop for maybe two hours, after which the 35Ah battery was supplying 6A to both run the laptop and recharge its battery.

That's a whole lot of assumptions and guesses, though, so it doesn't mean much. I may end up rewiring the battery box to include an ammeter so that I can monitor power use more rigorously.