Martin Meredith

I came across this delightful little arc of galaxies which make up 4 members of SHK 346 in Hydra. The chain itself is less than one arcminute in length. These are not particularly faint. I only have data for the uppermost and lowermost members of the chain. The uppermost is mag 13.0 -- but in the K band! The lower one is mag 17.9 in the B band. The fainter of the pair above the chain is 18.9 in B and listed at 2.1 billion light years distance. There are 8 members listed though as is often the case there are more than 8 galaxy candidates in the vicinity.

The reduced RC6 with the ASI 120 or the IMX224 seem like a good fit in terms of pixel scale, especially when binned 2x2, but the FOV is quite small (0.27 x 0.21 is what I make it). There are no shortage of interesting objects for that FOV but you might have difficulty getting enough stars to live stack, and getting the objects on the sensor could be a problem and/or issues with platesolving. My FOV is 0.44 x 0.35 which I regard as being fine but on the small side (I never have stacking or platesolving issues with this -- at least, for non-blind platesolving). On the other hand, your ASI 1600 gives a large FOV. Binned 2x2 the image size is not too large for live stacking. Likewise for the ASI 294. Main imaging cameras can make good EAA cameras esp. when used binned. In fact, quite a few people seem to use these cameras solely for EAA. Cheers Martin

Thanks Adrian. If your RC is f/9 then it would be great for some types of objects that we observe in EEVA time scales, such as the brighter planetary nebulae, but it would struggle with low surface brightness objects like this one. However, if you could reduce it down to f/6 or ideally lower it would be fine. I'm not very familiar with the RC design so I don't know how easy that would be. Cheers Martin

Over the years my approach to planning an EEVA session has changed. Until a few years ago I used to scour books like the Night Sky Observer's Guide for interesting-looking objects and prepare a list based around such gems. Nowadays I try not to peek beforehand, and prefer to leave the selection of objects to near-chance. What I've found is that there is nearly always one object that takes my breath away when it appears on the screen -- the unexpected object of the night. Sometimes it is an object from a list I'm working my way through; at other times it is something that looks intriguing on the charts. That was the case here -- the charts showed a large galaxy with a perfectly circular disc, suggesting either an everyday elliptical or an exciting face-on spiral. The charts classify it as SABc, so a spiral it was... The scene is balanced by the bright star, mag 6.6 variable GP UMa. I started off in mono but then added some colour both to reveal the nature of the acompanying star (which turns out to have a colour index of 1.6) and to see if I could get any further information on the galaxy core and star-forming regions. The core shows well, glowing orange-yellow in sympathy with the foreground star, and I think the arms have a pale blue look to them. The spiral arms of the galaxy are actually quite hard to tease out -- they needed a far more extreme stretch than I'd expected -- being uniformly faint compared to the bright core. There are a fewer obvious bright spots in the arms than in some face-on spirals. The bright spot that coincides with the galaxy label is a foreground star. A mono image stretched even further better shows the multitude of arms. The outermost arms are harder to see but reach as far as the two stars at the top. The area around the core is visually complex. The de Vaucouleurs Atlas of Galaxies classifies NGC 3184 as SAB(rs)c, ie spiral, of intermediate type between ordinary (A) and barred (B), and with characteristics of an inner ring (r) and yet also of spiral arms leading directly from the core (s). This is a kind of double-hybrid and sits right in the centre of the de Vaucouleurs scheme. I really recommend this book for anyone interested in galaxy types. The 'c' corresponds to a relatively 'late' type, with moderately unwound arms (some books call it 'cd' ie slightly later still). The bar is described in the de Vaucouleurs atlas as being a broad oval bounded by two bright inner arms. In common with several of the DSOs I've observed recently, NGC 3184 was discovered in 1787 by William Herschel. cheers Martin

And here are the remaining 'blue period' PNs I looked at over these last two nights (relative scales not preserved). These are mainly 1 minutes (4 x 15s subs) in each of RGB and L. The faint outer wings of NGC 2371 are visible in the colour shot but more easily seen in the negative view. Thanks to Bill S's image above for motivating me to look at this strange object. I also find the delicate 'sliced lemon' structures of NGC 1514 and 2242 very appealing for some reason.

Now to one that can be seen without narrowband filter: Abell 21 in Gemini. I've turned the saturation up on this one not only for the sake of the nebula itself but to better appreciate the very blue central star that looks like a hot pixel. All I can find on this is that it is mag 16.0 and type D0Z. I did happen to have an H-alpha in my filterwheel so I took a quick look using a L-H-alpha combination with the saturation turned up to a lurid level (must do something about those pink stars):

Here's one that I found near impossible to see last night: Abell 33 in Hydra, discovered by George Abell in 1955. The labelled blue marker is in the centre of the PN and the near circular boundary just about intersects the bright star (mag 7.2 HD 83535). The PN might just be easier to see in this negative image -- at least, I can convince myself that it is there. I think some new stretch techniques are called for to enhance local contrast... The central star, obscured by the blue circle in the image above, is very clear at mag 15.5/15.8 depending on the source. Abell 33 has a listed magnitude of 12.9 but a surface brightness of 24.8, which just goes to show that magnitude is nearly meaningless for these extended objects. In contrast, as a bonus, there is a mag 17.9 quasar marked at 10 o'clock in the upper image (though the marking is a little faint -- still working on the automatic annotation). This is pretty distant with a redshift of 1.9 (>8.5 billion LYs). It doesn't look clearly detected in the upper image but is definitely very obvious in the monochrome zoom. I completely failed to see Abell 18 in Monoceros, also discovered by Abell in 1955 (Abell was one of 4 discoverers of the objects that ended up in his catalogue). This has an even lower surface brightness of 25.9 and a listed magnitude of 17.0, so it was crazy to even look (except I didn't check beforehand). Even the central star is shining at a dazzling magnitude of 20.9... Nor did I spot Abell 31 in Cancer (SB = 26.6) although I did see the central star (no much by way of compensation...) Unfortunately I didn't have my Oiii filter in the wheel but I plan to revisit these at a later date with the filter. Next: more Abells...

Thanks Mike and Bill. I was fortunate to have another lengthy session last night during which I observed 7 PNs which I need to sort through (since 3 of them are Abells one can predict a few failures to see much although Abell 21 is glorious). One of them was Jonckheere 900 (J900) that Mike posted a while ago. Here it is in colour -- distinctly greenish and slightly oval (I am always concerned about tracking when I see this shape).

Here are a couple of many PNs I observed last night as part of a 4 hour session, making up for lost time. Both were discovered by William Herschel and, although I didn't realise it at the time, both are distinguished by astrophysically-interesting central stars. First, the blue-green gaseous glow of NGC 1501 in Camelopardalis, which has a complex filamentary envelope in 3D that is well seen on the Hubble image. One can just about make out a few strands in my image. The easily visible central star is mag 14.3 CH Cam, an extremely rapidly-pulsating ZZ-type variable (not looked up what the ZZ means yet) with an amplitude of 0.1 mag in around 20 minutes, so is something that is worth observing over an hour or so. The PN itself is less than an arcminute across. WH discovered NGC 1501 in 1787. The second Herschelian PN of the night is NGC 2440 in Puppis. In contrast to NGC 1501, which has a healthy (for Northern observers at least) declination of over 60 degrees, this one is at around -18 degrees but just about clear of the murk for me. Its central star is regarded as one of the hottest known white dwarfs. The central star is not visible here, at magnitude 17.7, being buried in the central pair of lobes. WH discovered NGC 2440 on this very day, 4th March, in 1790. I must say that when I started this thread I was not sure whether EEVA and PNs were a good match, but I am now totally won over. My standard approach these days is a minute each in LRGB in 15s subs and this works well for many PNs -- except for most of the Abell PNs I've looked at! cheers Martin

Interesting group with lots to see (1m45s is obviously enough to get a good image but not enough to savour all that is going on!). Is that a further companion galaxy just right of centre of the elliptical (within the halo), I wonder? A quick look on Aladin suggests a bulge in the right place but as is often the case the Aladin image is overexposed. There is a GAIA source in the right place but that doesn't necessarily mean it is stellar. Could be a supernova of course 😉 There have been SNs in that galaxy. Interesting to see the gx peeking out behind the star too. You can see its 'horns' (if I've got the right one). Here we have 'calima' (suspended sand) in the sky just to add another spanner in the observing works. Martin

Darks can be applied if they exist, as any previously-captured dark master of the right exposure length and temperature is automatically placed in a calibration library. Having said that, I tend not to take darks these days as I don't see many visible advantages. I have separate hot pixel removal so that accomplishes one of the most important functions of darks. In a remote setting darks are still easy to take with a filterwheel. Being a cheapskate I use a piece of flocking taped over one of the filter holders. Martin

Vlaiv, I think you are over-generalising from one example. I do perfectly well with my 800mm focal length scope and a Lodestar with around 570 x 750 pixels at 2.11"/pix, and have done so for nearly 7 years. Mike JW does great work with his Ultrastar and scopes up to 15". Likewise others with small sensors. It really is remarkable what one can observe with such a setup (see the EEVA observing section for 100s of examples of all types of object). There are various combinations of FL and sensor sizes that would be rated small by today's standards which are nevertheless perfectly adequate for optimal viewing of 99.99% of DSOs out there. There are plenty of advantages to small sensors besides cost. Fast download, easy to store everything you ever capture, and most important to my mind is that advanced processing can be done near live on small pixel count arrays that cannot currently be done with larger sensors. The entire user experience is different when the processing is fast enough to 'interact' with live at the scope. I realise this is counter-current, but I'm simply relating my own experience. Martin

An alternative is to get a small sensor and that way you won't need a coma corrector either. There are actually not that many objects that require a large FOV. The problem with FOV calculators is that they mainly show large objects, which is fine if you plan to stop observing after viewing 20-odd Messiers, but as the threads in the EEVA observing section demonstrate, there is an awful lot of other interesting stuff to observe. cheers Martin

Nephthys -- what a great field, Mike. There seems to be a whole load of faint galaxies to the north too. Lovely round stars too! This asteroid hunting sounds like a fun idea Geoff. I took a look at the data from the MPC, all 650M of it. It would be interesting to incorporate it into the platesolving routine at some point. Martin

That's a really great 'hexagon' SHK group. You don't often see much galactic detail in these groups (at least I don't) but here several of the members show some structure. It definitely looks like you've caught a mag 20.0 galaxy at about 1 oclock and a 19.4 quasar too (looking quite bright). The 15" seems to be performing really well. Envy... Martin

Really interesting to see what these look like with your 15". I imagine they are very rarely observed, as you say. I've tended not to add the more obscurely-named PNs to my observing list but maybe I should. I've tried a few Ms and Ks in the past without a lot of joy. I'll definitely check out J 900 in colour next time I'm out. NeVe 6 doesn't look like a PN. I've seen at least one Arp that looks similar to that fuzzy nest. Platesolving comes into its own for PNs. Browsing through some of my captures over the summer it has been interesting to see where some of them actually are (or missed in at least 2 cases). Martin

Very good to see this planetary in colour. The electric blue is spectacular as is the slightly pink 'eyebrow' at the right in your shot. I often use log for bright PN and have even been known to use linear! Martin

Great haul of PNs. NGC 2392 is really special as is the Medusa, hanging there in space like a ghostly crescent. I thought I'd visited NGC 2392 in colour but apparently not (blue with a touch of pink?). Here's a shot showing far less resolution than yours.This is a single sub, possibly too long at 30s; stacking didn't really help (produced a smoother result, but not what is needed here). Its impressive how you can get great results with a 15" scope and relatively small sensor (by today's standards). What system are you using for tracking? Martin

Thanks for the write-up. There are some fascinating examples in there. I particularly like 529, 801 and 1386 for their strangeness. In the case of VV 529 it would be interesting to know if those satellites are indeed galaxies or just very large structures in the main galaxy. Looking on Aladin it seems that one of them is a galaxy (chance line up?) while the other looks stellar to me. The VV catalogue throws up a lot of surprises. I checked if I'd observed any of these, finding that I have 5 recent observations of VVs in Leo, but no overlaps. Then I saw that there are 125 VVs in Leo alone, so plenty more to look at. Martin

Definitely a tough one, like many of the larger Abells. I'll have a go in colour but if it is hard to see in mono I doubt I'll be able to make much of an impression, but I ought to try with an OIII filter. This one needs a 48" and old-fashioned film photography, obviously... Martin

These are amazingly clean shots given the presence of the full moon -- a real testament to the way EEVA extends the viewing 'season' each month. I recall when I visited this group looking for 3 or 4 quasars in the vicinity in the mag 19-20 class. There are also some mag 18-19 galaxies with apparent distances in the 2.2-2.7 billion light year range strung out between NGC 3718 and NGC 3729. Lots going on in this field in spite of it all fitting into less than half a degree field of view. Small sensors at moderate focal lengths are great! Martin

Thanks Owen. I was looking for such an equation a few years back and never found it... Martin

Pretty good for 2s in colour! Glad to see you've got your EQ platform and dob working. Martin

Intriguing images. Looking at the Aladin SDSS9 layer I'd agree you've picked up these galaxies. Theoretically, a 15" scope at F3.5 with a sensitive sensor ought to get below mag 20. I'm impressed that this is possible in so 'clean' a way in a mere 1m40s made up of 10s exposures. I can't see magnitudes for these galaxies on Aladin apart from GAIA estimates. What's notable about the GAIA data is that the G magnitude (corresponding not to green but to the broad spectral band: see https://www.cosmos.esa.int/web/gaia/edr3-passbands) are similar to the range you label, but red magnitudes that are somewhat brighter in general. The point labelled 20.2 has a G of 20.6 and a R of 18.5 (and a B band mag of 19.9), suggesting to me that it is a strong emitter in the red and quite possibly near-IR part of the spectrum, where our sensors tend still to be quite sensitive (eg Ultrastar is quoted at over 40% QE at 750nm). So it would be possible to pick up some galaxies at a given quoted magnitude and not others at the same magnitude, depending on where they are emitting most (and also on their redshift I suppose). Looking at the GAIA passbands versus the Ultrastar, it seems the closest band is actually the GAIA B band (plus a little bit of the R). Nice work! Martin

Just to add, your NGC 4015 is Arp 138. Quite a field!