Messier Marathon Plans

Tomorrow night is Messier Marathon night and it looks like it may actually be clear!

Considering what we often see for the MM, this will be relatively balmy (wind chills in the teens above zero) and dry (the observing field is a little mushy, but there's no snow). It helps that this year it's being held in April even if that's not best for getting a high count.

Having gone over to the imaging side, that's what I'll be doing. To keep in the spirit of things I'll do mostly Messier objects.

Because the Ms are fairly bright I'll be using my DSLR. The targets will be taken from the two Astronomical League lists I'm working on, Arp galaxies and planetary nebulae.

Here's the list, Galaxies first:

• M49
• M60
• M65
• M66
• M87
• M90

These all have surface brightness between magnitude 21.3 and 22.3, so I think they can be imaged fairly quickly for modest quality results; it is a marathon night. Because M65/M66 occupy the same field of a TV-102 and DSLR, they require only one image. So for the six galaxies I'm expecting four to five hours of clock time including time for acquisition, composition and dark frames.

Next the planetaries and their surface brightnesses:

• M97 (22.3)
• Abell 21 (24.9)
• Abell 36 (25.5)
• Abell 35 (26.2)
• PN G164.8+31.1 (26.6)

You can see why the last four are not Messier objects; they're not very easy to see. Abell 21 is about three times larger than M97, making it a good target for the relatively short focal length TV-102 (700mm). Given its location in Gemini it might be the evening's first object and will get up to two hours of photons. The other dimmer objects will probably get passed over.

A Battery Box Addition

The Battery Box got one refinement over the last couple of weeks: A built-in 7.5VDC power supply.

I had intended to use an external supply, but the little Drok unit gets good reviews and is much smaller than the adjustable supply I had planned to use. It was perfect for mounting within the box. All it needed was an output plug. For that I went with the same sort of plug used on many mounts, a lockable panel-mount socket and plug. (Both were purchased on eBay.)

Drok 12VDC to 7.5VDC step-down converter

5.5x2.1mm socket and plug

A built-in converter presents two problems if it's left connected to a battery: A continual power drain (0.1 to 0.12W) and possible interaction with a smart charger. The drain doesn't sound like much, but it equals about 7Ah per month; that's a lot for a 35Ah battery. To prevent these problems I isolated the converter using a rocker SPST switch. As a reminder to turn off the converter when it's not needed I added a tiny LED that draws a minuscule 3mA. Here's the switch and LED:

Switch and indicator light

As I said, it's a tiny LED! It's just bright enough to let you know that the converter is active.

12V sockets (above) and new 7.5V socket (below).

I made an extension patch cord that fits the plug and the power cord from the camera's dummy battery; this will permit me to use other power supplies.

One other add-on is intended to make this easier to use: An accessory cable for my charger that will let it charge through one of the sockets. Because this is a small battery it can be charged at a relatively low amperage of 1.1A. While I haven't yet recharged it from a state of deep discharge, I'm hoping that it will remain cool during charging even when left in the box. It's my hope to never need to remove the cover.

NEXT UP: It's the Messier Marathon, April 8 or 9! I plan on imaging some Messier galaxies as a part of the Arp galaxy imaging project. There are six Messier/Arp galaxies I haven't imaged yet: 49, 60, 65, 66, 77, 87, and 90. Only 77 is badly placed; it will set too soon for imaging. Because it's a marathon night, I'll shoot only luminance with my ST-8300M, and probably only an hour apiece at most using my TV102. Last year the MM had only so-so skies. Here in Minnesota we're overdue for some good Messier luck.

A Big Night for Arps / A No-Show Star Party.

Tuesday night (10/6-7) was a nice night for piling up some Arp objects. Nothing really pretty here as I went for quantity over quality. Each object was given about a half hour of luminance using my C 9.25 operating at f/6.0. Here are the results:

These are presented cropped and scaled by 0.5X.

Tonight is the MAS's Fall Mini-Messier Marathon. It will probably be clouded out, but the alternate night (tomorrow) looks like it will be nice and clear. I plan on attending, not to do the marathon but to take a pretty picture of the Helix with the C 9.25 again at f/6.

I'm running at f/6.0 instead of the f/6.3 because after playing around with the focal reducer / sensor separation, I prefer how the images have come out at the slightly faster setting.

The No-Show Star Party of the title is the Eastern Iowa Star Party. I had planned on attending, but was unable to get any information from the hosting club other than the date and location. It's nice to know about things like amenities (AC Power, facilities, and fees are a few that come to mind.) before driving 5+ hours to attend. I strongly suggest to the QCAS (the Quad Cities astronomy club) that they post some information useful to potential attendees a few months before next year's EISP. So far as I was able to tell, they didn't post the party's date until less than a week before the event. If they want the party to maintain itself they need to get more information about it into public view in a more timely way.

The Next Imaging List: Arp Galaxies

A quick glance at the AL list of observing programs suggested to me that the next agenda item for me is the Arp Peculiar Galaxy Northern list. This lets you image any 100 out of 338 objects in the list, which is a lot nicer than the bright nebula list. The ALBN required 100 objects out of the 132 on the list that are visible from my latitude (i.e. having a declination northward of -45 degrees). There wasn't a lot of wiggle room for the ALBN!

The submitting requirements are much saner than the BN list. Apparently all that's wanted are the images themselves. There is this strange statement:

Also, photo enhancing of your image is not required, but, again, if you choose to do so then that will be accepted.

I'm not clear about what they mean by "photo enhancing," but everyone should do at least a simple stretch. I plan on doing the usual image processing to reduce noise and get as much as I can out of the images.

Most of these objects are fairly small. The largest visible from my latitude is M101; it nicely fits into the field of  my T2i when imaged through my C 925 @ f/6.3.

My plan is to image all 100 using the same scope and imaging device. Right now I'm leaning toward using the above T2i, just for the ease of getting color.

I'd also like to use the same exposures for all the objects. There will have to be some experimentation to see what that exposure might be. If the total exposure time turns out to be short enough (10 minutes or so), I might use in-camera long exposure noise reduction (LENR) instead of dark frames.