Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

Welcome to Stargazers Lounge

Register now to gain access to all of our features. Once registered and logged in, you will be able to contribute to this site by submitting your own content or replying to existing content. You'll be able to customise your profile, receive reputation points as a reward for submitting content, while also communicating with other members via your own private inbox, plus much more! This message will be removed once you have signed in.

Martin Meredith

Advanced Members
  • Content count

    1,142
  • Joined

  • Last visited

Community Reputation

1,355 Excellent

2 Followers

About Martin Meredith

  • Rank
    Sub Dwarf
  • Birthday

Profile Information

  • Gender
    Male
  • Interests
    Mountains, cycling, growing stuff
  • Location
    Northern Spain

Recent Profile Visitors

1,604 profile views
  1. Simply beautiful. The colours are really understated yet perfect for the cluster to stand out. Martin
  2. Thanks Rob. I could stare at Hickson 44 all night... Martin
  3. Of the 100 compact galaxy groupings identified by Paul Hickson, 11 are to be found in the constellation of Leo. They are perfectly placed for viewing in spring, and all 11 can be 'had' in a single relaxed EAA session, given a fair wind. Actually, gustiness was the main adversary last night, and it shows in the resulting observations. Still, I managed to take a long look at them all along with a few Arps on the side in a 2 hour session, with longer-than-usual stacks of up 8 minutes and a little longer in some cases. When you think about it, 8 minutes is still a very short time to be watching the details of these beauties emerge. The Leo Hicksons are numbered 38, 44, 46, 47, 51, 52, 53, 54, 57, 58, and 59. Actually, 53 and 54 are in the same (narrow) field of view, so the task is a bit easier. Here's some of my favourites. Hickson 46 LEO 10h 22 1.8 +17° 48 53.6 Smallish linear group in the centre of the shot; surprisingly bright. All four are either mag 16.4 or 16.5, hence one of the most uniform of all groups, adding to its appeal. The middle pair are so close they appear to be interacting. Three of the 4 are classified as active galactic nuclei. The group is flanked at each extreme by a pair of mag 19.8 (B) quasars (marked) with redshifts of 1.97 and 1.48. Hickson 51 LEO 11h 22 20.9 +24° 17 35.5 = VV 1435 Quite a dense group of 7, split into two subgroups. Brightest is the elliptical NGC 3651 at the centre, with a pair of galaxies very close in. The bright spiral at the base is NGC 3653, and the other spiral in the separate group of two at the top is IC2759. High redshift (z=3.3) quasar at mag 20.9 (B) close to upper group, visible only with imagination (but definitely doable on a less windy night). Hickson 44 LEO 10h 18 0.5 +21° 48 44.3 = Arp 316 = VV 307 Although I've observed this group before, I was struck by just what a fantastic patch of the sky this is: is there a better one for a small sensor? Various galaxy types are on display, from the elliptical NGC 3193 to the distorted SB spiral NGC 3187, and two SA spirals, NGC 3190 at the centre, and the Seyfert NGC 3185 at the right, showing an interesting ring-like structure. This is the most distributed of all the Hickson groups, being spread across nearly 17'. There's a fascinating paper about the discovery of a giant HI tail in Hickson 44: https://arxiv.org/pdf/1209.4107.pdf, possibly due to an earlier interaction with NGC 3162 which is now at some distance from this group. Hickson 53 LEO 11h 28 58.3 +20° 46 34.7 = VV 1441 Hickson 54 LEO 11h 29 15.3 +20° 34 42.6 = VV 498 These two groups are visible in the same field. Unfortunately, the wind got up at this point and it shows. The larger group is Hickson 53, consisting of the elliptical NGC 3697 and 3 much smaller members, the faintest of which is just to the upper left of the star near the base. There is another uncertain galaxy near the galaxy pair looking like a speck of dust. This is just 0.1mag fainter than the faintest Hickson member so didn't make the cut. Hickson 54 is the most compact of the entire catalogue, occupying just 0.73', less than 20th of Hickson 44. Believe it or not, there are 4 components here. Zooming in, 3 separate bulges can be made out. This is a real tough one but likely to be resolvable with the right conditions. Hickson 57 LEO 11h 37 50.5 +21° 59 6.0 = Arp 320 = VV 282 = Copeland's Septet This is a well-known group of 7 NGC galaxies, to which Hickson added a mag 17.0 8th member. The warped NGC 3753 appears to be trying to swerve its way past its close attendants. One thing I never noticed until last night is the sparse cluster of galaxies to the right of the Septet. This may be a random collection -- Leo is so dense in mag18+ galaxies hereabouts. Hickson 58 LEO 11h 42 11.8 +10° 19 1.2 Although its centre is in Leo, this group pretty much straddles the border with Virgo. Of the 5 NGC galaxies making up the group, the central member, NGC 3817 is itself right on the border, which runs perfectly parallel to the lines of declination as if some colonial ruler had drawn it. Although Hickson 58 is a marvellous grouping, especially the spiral NGC 3825 with its prominent pair of arms, I was drawn to the coincidental placing of the distant galaxy cluster Abell 1354. In contrast to Hickson 58, whose members are around 300 MLys distant, the mag 18-20 'fireflies' of the Abell cluster lie at around 2 billion LYs. This conjunction was the find of the night for me. If you look closely, the whole shot is covered with galaxies, with a particularly rich group in the upper left, which is part of another Abell cluster (1356). There are even faint galaxies hiding behind the skirts of NGC 3817. There are 6 Abell clusters within about 1 square degree in this part of Leo. What struck me seeing these groups in sequence was the tremendous variety in the Hickson catalogue, from the least compact of all Hicksons to the barely-resolvable most compact group. Lots to come back for on a still night... Cheers Martin
  4. Hi David Glad to see you've now got your kit together. Exciting times! A few comments I have the Baader set bought as a pack of 8 (3 narrowband, RGB, L and C) at a decent price on Amazon (though it doesn't look like there are any good deals at the moment). I find them parfocal enough for me (I haven't noticed them not being parfocal, that is, although a close inspection might -- or might not -- reveal some issues). I have a motor focuser kit that I bought ages ago and haven't installed. Having got a Bhatinov mask (an *essential* accessory!) I focus once only at the start of the session and it takes about 20 seconds, using the bright star I complete my 2-star alignment on. Perhaps with an autofocuser and the right software you could get away with non-parfocality. I don't know because I've never used an autofocuser. But it might slow you down. For instance, when doing live RGB on clusters I can get the next filter in place and the next exposure going with about a 2s gap... not sure how long an autofocuser would take. You want to minimise gaps between subs if doing live combination simply to make life easier for the stacking/rotation, although tolerances are generally ok. As part of the filter set I have the Sulphur filter, but have found very few objects so far for which it gives a worthwhile signal for EAA use (the Crab is an exception). Re light pollution, there is some info here about the gap left between the Baader G and R filters to reduce light pollution from sodium/mercury lamps -- not sure how we stand with LEDs though. Newtonian tweaks: * Bob's Knobs for the secondary; if you mention which scope you're using, he'll advise if any are needed for the primary I believe. I didn't need them for my Quattro. * plastic (milk bottle) washers placed under the tips of the collimation bolts smooth out the jerkiness of secondary motion (Even so, secondary collimation is a pain! but I think you're at f5 so less critical) * Flocking at the upper end (Wilco sells cheap suitable material for about £6 a sheet) * I've also flocked the back of my mirror; this I think helps a bit in reducing the amount of light (think laptop screen?) entering at the mirror cell end of the scope. AstronomyShed have some nice youtube demos showing how much light enters at that point if you're not careful. You can combine with a fan holder too which doubles up as a light shield at that end. I don't use a cooling fan. I put the scope out about 1 hour before I want to start observing (though some of that time is occupied with checking collimation, polar alignment, focusing and gathering darks). Additional stuff: I find a good dew/light shield is really helpful. I almost never suffer from mirror dewing up even when the outside of the scope is dripping wet (I live near a reservoir...). Depending on how much you find your coma, you might want to invest in an autocollimator at some point. But at f5 the case is marginal. Hope this helps, and looking forward to some nice galaxy pics. Martin
  5. The Ultrastar + StarlightLive combination is reviewed by Ade Ashford in April's Astronomy Now. It's great to see SGL member Paul81's software getting this kind of (rave) exposure. The article is a good showcase for video astronomy/EAA in general and the power of live stacking on alt-az mounts too and I hope will attract more people to try it out regardless of camera/software. The piece is certainly a good place to start for newcomers to EAA. Martin
  6. In case its of interest, I got a quick shot of it last night in my 8" f/4 Newt using Lodestar X2 mono camera + filters. As Paul says the core is quite bright but I couldn't find any sign of a tail. This is 2 minutes in each of RGB. The core isn't really multi-coloured: this is the result of the comet's motion in between R, G and B filters; no special comet processing done during the live capture. I was hoping to see a tail but I ought to have used shorter exposures to minimise the motion. Martin
  7. Thanks Mark. I didn't know that asinh did that. In fact, asinh is one of the options in StarlightLive and in my experience it does produce a change in colour balance compared to linear. Maybe the implementation is different. I'll take a look at your CN thread. Martin
  8. Ursa Major is home to more than 30 members of the Arp catalogue. Here are 7 displaying very different kinds of peculiarities that I looked at a few weeks back. First up is Arp 1 (NGC 2857). This mag 12.2 galaxy is classified as a low surface-brightness spiral, although I've seen fainter. In the same field is Arp 285, consisting of mag 13.0 NGC 2854 (the NE component in this shot) and NGC 2856. This latter galaxy has a narrow jet that I was not aware of when I observed it (otherwise I would have spent more time on it). It is clear on the DSS image and just barely visible at a push on the inverted shot (rotated to match: it actually points towards Arp 1). I believe this is the remnant of a bridge formed from galaxy interactions. Next is Arp 18 (NGC 4088), also in Ursa Major. This galaxy, certainly meriting the appellation 'peculiar', is a "spiral with detached segments", clearly seen here. This is a mag 10.5 galaxy with a compact nucleus, surprisingly bright arms. As a bonus we also have spiral NGC 4085 in the shot. Somewhere between the two galaxies is a mag 20.7 high redshift quasar that I've failed to capture. Another one to revisit. Here's Arp 27 (NGC 3631), a "spiral with one heavy arm" whose location I've indicated in gray. Arp also talks about an 'absorption tube crossing from inside to outside of the S arm' (the S arm is on the right in this image). I'm not sure what he means by an absorption tube but there is a very narrow curved structure that seem to sprout out of the arm at about 2 oclock. Also marked is a reasonably bright yet distant quasar, somewhere in the 8.5-10 billion year range. Downsizing now, in the centre of this shot next to the bright mag 8.6 star is Arp 151, not surprisingly a member of the category "galaxy with jets" -- the jet pointing upwards towards 11 o'clock. The end of the jet (SE here) is the stellar-like active galactic nucleus Markarian 40. Arp 224 (NGC 3921) looks like a pearl ring but is classed as "Amorphous spiral arms". I left this stacking for a while longer to get a better look at the complete ring and also the faint extensions on the opposite side of the loop. The area immediately to the left of Arp 224 is Abell Galaxy Cluster 1400, which is a smattering of mag 18+ galaxies at around 1.2 billion light years. A fair few are visible here. Arp 224 is at about a quarter of the distance, as is the near edge-on spiral NGC 3916, perhaps the cause of the loop structure? Finally, here's Arp 264 (NGC 3104). Here the monica "Irregular clumps" fits. This is a very strange object and quite faint, needing a good stretch. Actually, this one is not quite in Ursa Major but just over the border in Leo Minor. Thanks for looking Martin
  9. Very impressive given the conditions moon-wise! I struggled with Thor's Helmet. Martin
  10. Interesting post. This is a topic that fascinates me too. I've noticed that applying any kind of compressive nonlinearity during the stretch tends to produce bluer stars. I put this down to the blue channel (typically) being weaker in the unprocessed image, which results in B getting less compressed relative to R and G, changing the colour ratios in B's favour. If I want to preserve good star colours I typically do only linear processing, although it would be good to find a process that maintains colour ratios and allows nonlinear stretching. [aside: I was playing around with some coding for HSV, stretching only the luminance component, and then re-inserting the H/S preserving the original colour ratios, but it didn't go anywhere. At some point I want to look at chrominance + luminance representations like L*A*B.] Have you looked at any external colour reference data for any of your images? Which cluster is it, BTW? Martin
  11. Hi David I think in what you're proposing the mount is the weak point. I believe hard core imagers take the official rating and halve it. EAA is not quite so demanding but the longest useable sub length is going to be reduced, which might point you more in the ZWO camera direction. My mount (az-eq6) is much heavier ~ 16kg + 10kg of counterweights. The scope (carbon fibre) is easier to handle than the weight suggests as it is quite short at f/4. I use a very light Rigel unity power finder instead of the supplied finderscope to knock off a few more grams. Info on Quattro weights How far would you need to carry the setup? It can be quite a pain to move all the individual parts and have to setup the entire thing. I'm fortunate in being able to carry it mounted (usually minus one of the counterweights) for a few metres from house to terrace and back, but any further and it would have to be dismantled. A lighter scope/mount would then be the order of the day. But I would still aim for the fastest scope at any given aperture. Just to add: if I were starting out in EAA with a view to getting into filters, I would start out with a mono camera anyway. It is going to be more sensitive, easier to manipulate in software, and essentially all that is needed to produce good deep views of many objects (particularly galaxies). Most of my sessions are still in mono. I reserve RGB for clusters (I don't do much nebula observing). I started out with a colour Lodestar but as soon as I could I bought a mono and didn't go back to the colour even though it was a while before I got my filters. cheers Martin
  12. Amazing what he is able to achieve visually. Have you seen his article in April's Sky and Telescope on this topic where his observations are compared to deep photos? Martin
  13. Thanks elpajare and Dave; I know, stash_old, but I think the run of good luck has now come to an end for a few days at least.... Martin
  14. Hi David A few quick answers: I believe many use SharpCap with the ZWO cameras. I've only ever used StarlightLive but lots of people judge it to be the easiest and yet in some ways the most powerful too. The ZWO menagerie is not one I've ever tried to get my head around. But I think that the 290 has a lot of fans, as does the 224. I recall a thread some months ago on CN saying why the 178 is not such a great choice, but I can't lay my hands on it at the moment. Maybe it was this one. Still, best to get opinions from owners! For me, purely based on the images I've seen posted, I find the Infinity a little 'soft' and with a colour cast. Almost certainly these things can/will be 'fixed' in software in the future if that's what users want. Check this thread. I don't feel undersampled with my 8" f4 setup. But I'm at 2.11"/pixel so I don't really regard that as likely to be significantly undersampled. Seeing is never great around here but I find it adequate on most nights. The route of using a Barlow is a possibility but it does inevitably slow down the system a lot. cheers Martin
  15. I've had a good run of 6 clear moonless nights out of 10 and I've spent most of them observing open clusters. Monoceros in particular is well-placed and chock full of them (128), as is Auriga (99) and of course Cassiopeia (183). For those with a decent southern horizon, Puppis isn't far behind with 173. I seem to have clocked up 55 in 6 sessions (along with the inevitable sidetracks to nearby galaxies). Each cluster is different. I've adopted a strategy of watching individual subs in mono as they come in and then at the last moment switching to the coloured stacked version. It comes as quite a shock to see the vibrant tones appear on the screen. On Saturday I focused on some of the older clusters, and last night on some younger ones. I must admit to developing a real fondness for the older clusters with their shimmering faint star fields. First up is Trumpler 5 in Monoceros, to be found in the north of that constellation, with a higher declination than nearby Betelgeuse. This is one of the oldest known open clusters, with an estimated age of 5 billion years. It is also a rich and not particularly faint cluster with over 500 suspected members, including a very red carbon star, V493 Mon, visible here just below and to the right of centre. Its distance is thought to be nearly 8000 LYs. However, Monoceros contains an even older open cluster in its southern reaches, not far from Puppis. Berkeley 39 has an age estimated at 8 billion years, and at 15.5 million LYs is located at nearly twice the distance of Trumpler 5. It is the 8th oldest known cluster. (the red 'star' left of centre is a hot pixel I think...) The listed position is some way off in declination. The most distant listed open cluster in the Dias catalogue is Berkeley 29 in Gemini, which is thought to lie at an incredible 48500 light years. This is relatively young at only a billion years. Who knows whether it will last for another 10 billion? It seems quite depleted to me (75 members) but that might just be the distance. Again, the catalogue position seems to be off by a few arc minutes of RA. The visibility of all these clusters is aided by being in the direction away from the galactic centre. At the other extreme of age, one of the youngest known clusters that is convenient to observe at the moment is NGC 2244, at just under 2 million years old, lying at a distance of over 5000 LYs. This is the cluster embedded at the centre of the Rosette Nebula also in Monoceros. Normally I use linear brightness scaling when doing live RGB combination in order to preserve the 'correct' RGB colour ratios, but given the presence of the nebula in this case I used nonlinear scaling to capture both it and the stars. The effect is to add a blue-cast. (I believe this is because the scaling function preferentially boosts weaker signals, which in this case is the blue channel). I read somewhere that although there are just over 2000 open clusters listed, this is a tiny fraction of those present in our galaxy; the obscuring effects of dust and the great distances presumably make the others hard to spot. Thanks for looking! Martin