ollypenrice

I agree that redshift/blueshift don't need acceleration (as Jim also points out) but a body's proper motion does, surely, need to originate with an acceleration? What I'm getting at is that the OP's question is about movement since he asks in which direction the stars are moving. Is there not a fundamental difference between a body 'moving' because of the expansion of space and 'moving' because it has, at some point, been accelerated? If not, why do cosmologists distinguish between Doppler and Cosmological redshift? Olly

But where did this uniform motion originate? Olly

I'm always nervous around Vlad (despite his being such a nice chap! ) but here goes... There are two kinds of redshift. Though they are mathematically equivalent, their origins differ - because there are two kinds of 'movement.' 1) The Doppler redshift. This is created when the star or the observer (or both) are accelerated by some force. This kind of acceleration must have a direction and we are familiar with 'movement' in this sense. In this case we would talk of the star's proper motion. (It's own motion.) 2) The cosmological redshift. This applies on cosmological scales, outside gravitationaly bound systems, and does not arise from an object's being accelerated. Although the galaxies on this scale are moving away from each other, each one considers itself to be more or less at rest (ignoring the fact that they are all whirling around to some extent in curved spacetime.) In this unfamiliar situation each galaxy experiences no movement of itself but sees all the others as moving away from it as the space expands between them. Describing the way in which they move apart from each other requires a metric for the expansion of spacetime. Any one galaxy will find it easy enough to describe all the others as moving away from it along radiating lines like shrapnel flying from an explosion. That description, however, will not work for more than one galaxy because each one will see itself as being at the centre of an explosion - and they can't all be right! Olly

It's an edge artifact from the Ha layer and I thought I'd fixed it in the latest version! I'll check it out again. Thanks, Wim. Olly Edit: Fixed.

Managed to squeeze a bit more out of the Ha: Olly

That's really good. Olly

Very good indeed. For me the colour is a bit 'green high, red low.' Olly

From Kit Marlowe's doomed Dr Faustus, perhaps? See, see, where Christ's blood streams in the firmament! One drop would save my soul, half a drop: ah my Christ! Olly

Sexy title, eh? This is a three-up effort with Paul Kummer capturing and pre-processing 3 hours per panel (2 panels) in the RASA 8 and Tom O'Donoghue devoting 18 hours (eighteen) to 3nm Ha in his Tak FSQ106, based here robotically. My post processing. This supernova remnant is in Auriga and shares the field with an assortment of LDN objects. Despite the 18 hours the Ha was agonizingly faint and had to be tortured horribly to get as far as this. So, a nice round 24 hours' worth: Bigger one is here: https://ollypenrice.smugmug.com/Other/Emission-Nebulae/i-24vBwxW/A Edit. Please scroll the thread down for final version. Olly.

You absolutely do need flats. They are truly at the heart of things in AP. Olly

Indeed! However, I've no idea how one might go about making a widefield image from a single focal length. Is it even possible? lly

Very helpful, George. Thanks. You're in safe hands with Dave Wills, he's a good guy. Olly

You can be absolutely sure that we all send her our best wishes and condolences. Olly

Valid question. Our situation is that we want to squeeze a fifth robotic instrument into a roll-off roof shed designed for four piers. The instrument is just a Samyang 135 lens, so very small, and we can get away with squeezing this setup in if it is free of counterweight arms, etc. The AM5 mount and camera are perfect for the limited space available. At present the Samyang is occupying a main pier and this isn't necessary, it's overkill. Olly

Quality takes time. Nice one! Olly

Tom did the postage and packing. Regarding printing, even when you follow the correct colour protocols you'll want to see a test print or two first before committing to a big one. I now do my own prints, up to super-A3, and find results unpredictable, so I'll do several 10x15 tests first, adjusting the image accordingly. Usually this has to do with the brightnesses at the bright end but blue saturation can often be sky high for some reason, even with a calibrated monitor. Tom went to the printer in person to run through this procedure. A 1.0 x 1.8 metre print costs several hundred euurs so you don't want to lose one! Olly

Perfect. Thanks, Peter. Olly

Well spotted. The difference is just half a point in Ps Colour balance, midtones, away from green towards magenta. That's one point, faded by 50%. Because I wasn't confident about the background reds I reduced their colour saturation early on. Olly

In the end I decided it was in the data, though this may be wrong. It's been through DBE. There is certainly what looks like IFN in the top right. I do think the small star count might be lower in the redder regions, suggesting the presence of obscuring dust. I think when the capture is very deep it's reasonable to expect variation in the background but it's very hard to tell. I can see absolutely no trace of the green glow seen in BrendanC's image in an Equalized version of our data and have to conclude that it must be spurious. Olly

The 255 hour image on AB does show some field Ha which you might pick up. Probably worth a look, though they said it was very faint. Olly

Wow, Rivington must have livened up a bit since I last lived around there! (That would be fifty years ago...) I think the Trough of Bowland would be darker but it's further away. Olly

I was intrigued, this morning, by the feature looking like a tidal tail emerging from NGC5198, the elliptical to the right of M51. First I wanted to check that it wasn't an artifact and a careful look at the data, equalized in Ps, suggested it wasn't. I then found a couple of comparable images, including a good one by Dave Wills of PixelSkies, which also show it. Dave describes it as 'recently discovered,' as do a few other imagers who've captured it. I haven't yet found anything about the discovery but will keep looking. Yet again, the RASA shows us that 'deep is fun.' Olly

A mighty fine piece of work. We use the same lens-camera combo and, like you, find that it works! Olly

What was your image scale with the 12 inch? I'm just wondering if you were oversampled, in which case resampling downwards before processing might be good for the faint stuff. I also wonder if it might be possible to downsample still more, stretch the hell out of the tidal streams, denoiose them and then resample them back up again to blend with a conventionally processed main spiral. Thinking out loud. Olly

A huge loss. The first thing to say is that he was, quite simply, an extraordinarily nice man. He was so 'available' to the amateur community that, like many others, I met him several times and pestered him with questions which he answered with endless patience. What a very, very sad blow. Olly