M4 at motorway speed

[Placidus]

We were very inspired by Louie's (Atalas's) recent M4. We had half an hour to fill in (in our freezer suits at -1C) while our main target appeared above the scope slew limit, so we thought we'd get as close as we could to Louie's shot.

Rattled off 30 one-minute subs on M4. Both seeing and, ominously, guiding and even focus seemed to vary a lot from sub to sub. We threw out ten dodgy frames and kept the remaining twenty.

Cracked record: We have very much in mind that globular clusters are extremely ancient objects, and therefore most of the stars must be very cool and hence reddish in order to have lived that long. Only a few are hot and bright as a result of recent collisions increasing their mass, and therefore only a few very salient ones are bluish.

Mindful of recent discussions on saturation, we've tried to set the colour balance and saturation at the point where we can clearly see the different colours (which is kinda the main message after all), but no further.

We've also pushed the contrast to the point where M4 is the subject, not the Milky Way behind it.

North is on the left, because that way an Aussie farmer will immediately recognize the face of a Merino sheep looking straight at the camera.

Presumably by luck, there are several interesting streamers of faint and pinpoint stars forming apparent straight lines (from our point of view) heading toward the bottom of the image.

Aspen CG16M on 20" Planewave on MI-750 fork. Seeing fair at about 2.2 sec arc. New moon, very clear, no wind. Field 36 min arc, 0.55 sec arc per pixel.

Big image here (https://photos.smugmug.com/Category/Clusters/i-Fnzb824/0/ecbaacc6/O/M4%20RGB%207%20minutes%20each.jpg)

Cheers,
Mike and Trish

[atalas]

I see the sheep! I see the sheep! nicely resolved and I must say this is more the star colours I was expecting in my shot too but,the light never seemed to bend that way.

Like always a great job guys and in such short exposures too :thumbsup:

[Placidus]

Thanks Louie! :)

[Peter Ward]

I know I should not have mentioned the war...but the stars look a little overweight and horizontally smeared...but maybe I can get away with it :)

[strongmanmike]

That globular must have done something naughty :shrug:.....it is looking rather sheepish :P

Nice one guys, that glob shines through a fair bit of dust if I am not mistaken, so it would be rather reddened.

Mike

[Placidus]

Everything you say is true. The horizontal smearing seems something we have to put up with. A much longer total exposure would overwhelm it; it's brought out by a strong stretch. The fat stars are bothering us. We saw periods of reasonable seeing, and periods where (in the 60 seconds available) the guiding was all over the shop, and one frame even looked out of focus. Last night I watched very carefully. Nothing wrong with motor control (0.2 sec arc of requested), the focus motor wasn't jumping about, and guiding was good. Perhaps just bad seeing. But if Santa bought us some adaptive optics, it would have really cleaned it up for the M4.

One good thing to come out of the exercise: We like doing one-hour exposures when doing faint things in NB. What this image shows is that the fat stars are there in the first 60 seconds. It's not the one hour that is the problem.



Thanks muchly Mike. :)

We hope we have captured at least something of the reddening. We've shown it as much more orange-red than most folks do.

[multiweb]

Uber resolution on this one Mike. Resolved to the core. :thumbsup::thumbsup::thumbsup:

[Placidus]

Thanks, Marc.

[RickS]

Not perfect, but pretty dang good :thumbsup:

[Stevec35]

It's a good globular and seems to show up well in just about any exposure. Nice star colour.

Steve

[Placidus]

Thanks, Guys. They are so beautiful and sparkly in the eyepiece. Hard to capture that sparkle on screen with just eight bits, but one can legitimately help out with the colour.