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Martin Meredith

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About Martin Meredith

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  1. Hi Mike As I understand it this is a way of expressing distances in terms of the magnitude the object would be if seen at a fixed distance of 10 parsecs. So an object with a distance modulus of 0 would be at 10 parsecs, one whose distance modulus is -1 would be closer, and one with modulus 1 would be further away. Like magnitudes, these are based on a logarithmic scale, meaning we can use relatively small numbers to maintain precision while accommodating vast distances. Since it is a log scale, to convert back to real distances one has to raise to a power (the inverse of logarithm). The actual formula used in LEDA (as I give above) is explained here: http://leda.univ-lyon1.fr/a007/index.html See also explanation of distance modulus here: https://astro.unl.edu/naap/distance/distance_modulus.html and https://lco.global/spacebook/distance/what-is-distance-modulus/ HTH! Martin
  2. Hi Mike In LEDA distances are given in some other type of unit and need to be converted using something like this: Dist = round(3.261633 * power(10,(modz-25)/5)); % in LY where modz is in the units LEDA uses for distance Martin
  3. Nice shot! LEDA gives about 1720 million LYs. LEDA also suggests there are NGCs that are further away but I don't necessarily trust all this data. This is a list ordered by distance.
  4. Beautiful image! In case it is useful, here's a chart showing galaxies down to mag 20 or so, occasionally deeper (needs to be turned upside down for comparison). I think you've gone deeper than this chart! COM4937.pdf Martin
  5. This is a very nice grouping. In fact, it is the central part of Abell-Corwin-Orowin galaxy cluster 539. Here's a shot from some time ago, complete with hot pixels... It really needs an even large field of view. Martin
  6. It looks like I've captured 90, 91 and 86 but not the rest (yet!). I must revisit the Hickson marathon idea as it was a few years back when I worked it all out. Unlike the Messier Marathon, this one has to be done toward the end of November if my computations are correct. And a location like the Canaries would be ideal! Martin
  7. Congratulations on getting all the Hicksons visible from your location! That's some achievement. I'm pretty close to having them all but am too disorganised to work out what I am missing... Which are the 7 you can't see? BTW I worked out one day that it is just about possible from Spain to see all the Hicksons in one night -- a kind of Messier marathon for EEVA perhaps. I've not got round to it yet though. Martin
  8. Hi Vlaiv In the psychophysics literature these things are known as JNDs (just-noticeable differences) so if you search for this term you are bound to come across some relevant scientific studies. A good astronomy-related resource is chapter 2 of Roger Clark's book Visual Astronomy of the Deep Sky. (The relevant pages appear to be accessible on Google books). cheers Martin
  9. Congratulations Mike! What an achievement. Pretty impressive to catch 330 in under a year. Looking forward to your next challenge. Martin
  10. Hi Mike Have you checked this thread: Looking at the table, I don't think you'll see such a big difference between the Ultrastar and the 174 (sure, there are some diffs, but perhaps not enough to be worth changing). The CCD will be easier in use due to not having to specify the gain, and the normal read noise advantages of the CMOS are no so apparent in the 174 it seems. I think I'm correct in saying the 224 is colour (hence not in that table) while the 174 is mono. The 290 gives a much smaller FOV other things being equal (and IMO a not so useful aspect ratio). Having said that, it is a good EAA sensor in terms of read noise and QE. Martin
  11. Hi Mike That's a great capture of Arp 98. I feel I should revisit this on a moonless night. VV 1034 is another where it ought to be possible to tease out more detail. Here's the DSS image which shows the graceful arms. Martin
  12. Thanks everyone. Nice to see Jocular being promoted -- thank you! Martin
  13. As I was inputting the date on the mount last night I noticed it has been many weeks since my last session, way back in October. November here was the wettest on record. So when the sky cleared just before dusk it was too good an opportunity to miss in spite of the 50% moon. With no clear plan I just headed for Triangulum and looked at what I could find on the charts... I used 15s subs throughout although the last two objects would have benefitted from longer subs (but I found field rotation to be a bit of an issue for longer subs in this part of the sky with my alt-az mount). No calibration frames. StarlightLive was the capture engine and Jocular used for everything else. Other details are on the images. I always start with something obvious to check the I haven't made some silly mistake during 2-star alignment and the obvious thing in this constellation is M33. This is a little too large for my sensor but even so a lot of detail in the arms can be captured. The next 'object' is VV 338, an interacting(?) pair consisting of NGC 672 (the brighter of the two) and IC 1727. I observed this for quite a long time as more details were emerging with each sub. The IC galaxy has an interesting structure with several knots lined up along its central part, and a highly-disturbed outer part, resulting in a 'umbrella handle' hook at the top. On the DSS image there are many blue (presumably recent star-forming) regions. This would respond well to colour. Sticking with the VV catalogue of interacting galaxies, here is a field with two such groups, VV 1034 being the group to the upper right with the face-on spiral, and VV 1035 the very close pair below-left of centre. For VV 1034, the face on is NGC 974, type SABb, and to its right is type S0 NGC 969. It is well worth looking at the DSS image for these galaxies as the spiral in particular has a beautiful appearance which I have failed to capture, including some extremely graceful and thin arms. For some reason my charts actually identify the very close pair sitting above these two galaxies as VV 1034 (one of these is NGC 970 while the other has a lesser denomination). VV 1035 is identified as NGC 978 but is clearly a pair of galaxies (listed as E/S0 and S0). There are a few mag 18+ galaxies visible in-between the two VVs Next, a quick look at a galaxy close to the VV groups that appeared to be interestingly flat on the charts and turned out to be so. This is NGC 973. (actual exposure is 9 x 15s = 2m15). This is reminiscent of NGC 891 with its central dust lane cutting the appearance into two. The galaxy below is IC 1815 and has a similar distance of around 240 MLYs, so I wonder if these are also interacting. I can never resist looking at Arps. This is one of two Arps in Triangulum and I have to say it is one of the faintest I've observed, requiring a lot of stacking to pull out its peculiarity. This is actually a close pair of galaxies at 599 MLYs distance where the slightly brighter lower galaxy (mag 16.1) shows little distortion, but on close inspection the upper galaxy (mag 16.4) has its long arms drawn out by the interaction. Unlike the other images here (where N is up), I've rotated this to show the appearance as a back-to-front question mark. Again, this is very clear on the DSS image, and in fact the arms are blue along their entire length, something worth returning to on a moon-free night with colour I think. I ended the chilly and relatively brief session seeking out a very distant object for a non-astronomical friend with whom I'd been chatting about distance scales in the universe. This is an unspectacular but nevertheless compelling object: a z > 4.5 quasar, corresponding to a distance of between 10 and 12.5 billion light years depending on the adopted model. It is listed as V mag 18.8 (which looks about right) but I had a hard time at first with this one (and I'd barely count it as an identification but it does just about rise above the noise floor) hence the longish stack. I guess some calibration would have helped...The more precise coordinates are 1h 34 21.6, +33° 7 55.9. Thanks for looking! Martin
  14. Fascinating galaxy and indeed field. I tend not to do much colour work with galaxies but in this case it is really nice that you're picking up the blue of the 'knots' in that galaxy (it's very interesting to compare with the DSS image where the blue is very clear also). Martin
  15. Very nice shots Mike and great information. I am further south and checking my images of these objects I don't think I've managed to pull out anything extra... Martin
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