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I cannot answer the question how long the silver coating will last from my own practical experience, as I am new to this. Time will tell.
The short answer must be “it all depends.” Having purchased a decent quantity of all the chemicals required, the cost of each re-coating is small.I have found this informative article on the Sheffield Assay Office website:
https://www.assayoffice.co.uk/news/ever-wondered-why-does-silver-tarnish
They surely know what they are talking about. Clearly their advice is not specific to telescope mirrors but the priciples will be the same.Presumably anti-tarnish paper could used to line mirror covers. The paper is available on Ebay in small quantities. The jeweller in a local town can order in bulk, by the ream. My dictionary tells me a ream is 516 sheets! I don’t yet know at what cost.
I have a recollection of reading in an old book that alum paper will delay tarnishing. The item included a recipe for making alum paper.
Callum, yes, I will prepare a paper for the Jounal once I’ve gained a little more experience. I suspect it is a process where you learn sommething new each time.
This photo shows the result of my second go at silvering a few days ago, using kit I’ve put together from “bits and pieces”.
The two spray guns used for applying the silver solution and reducer were fished out of our recycling bin – Waitrose Shower Shine bottles!
The silver coatings achieved are not 100% perfect but are good enough to use and I feel sure I will get better at it at each attempt.
As Callum suggested in a post on 10 June, the mirrors did not require burnishing.Attachments:
Giovanni, you are right, silvering was a thing of the past. As early as 1961 J.B. Sidgwick wrote that vacuum coated aluminium had taken over, noting also that the silvering chemicals were difficult to obtain by members of the public. I remember trying to obtain potassium nitrate for a different purpose and thought they were going to call the cops. Now almost anything is available mail order. I suggest the cost/benefit is perhaps shifting back to silvering. It is not just the cost of aluminising. There is no way I am trusting my mirror set to a courier, when a master optician said in 2016 that to make it then would cost between £6k-£10k. So I’d have drive it there myself and collect it afterwards.
If you can, read Jerry Oltion’s short article, pages 74 & 75 in Sky & Telescope January 2020,Richard, thank you for the encouragement etc. I did attempt silvering 4 and 6-inch test pieces back in 2016 following the method of E. E. Hall in the 1965 June Journal. Results were patchy. Revisiting my 2016 notes today I seem to have missed out the cleaning/degreasing – oops! I do have 60% nitric acid in the cupboard so can use that as you suggest although it is horrid stuff. I will try using calcium carbonate first, as per the Youtube videos.
I had assumed the sprayers being used were ‘proper’ big-ticket paint sprayer kit but I now realise they are no more than the cheap greenhouse/garden things sold by garden centres.I am also intrigued by the idea of perspex chips dissolved in a solvent as a guard coating. I have read that alum paper can slow down the tarnishing and will try that first.
Giovanni, interesting to hear your experiences. I have a pet theory as to what else is going on – it’s aircraft exhaust. When the Iceland volcano erupted in 2010 halting aviation, the change I witnessed to my sky was dramatic and nearly instant. Normally there are so many aircraft leaving so many contrails. My record is 11 jets counted simultaneously from my garden. Back in the 1960s a British airline ran a TV advert – people in the street looking up at “the 8:50 Trident” spearing across the sky, glancing at their watches and seeing it was on time. If only we’d realised then that half a century on there would be an 8:50 and 10 seconds Trident, and an 8:50 and 20 seconds Trident, and an 8:50 and 30 seconds – you get the picture. It surely can’t go on at this intensity. Trust me, every wisp of cloud in this photo is artificial.
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Alex P, Grant P – regrettably Grant is right. Trust me, my neighbours (effectively only two within a half-mile radius) don’t care. So long as they are alright, that’s all that matters to them. The Council route is closed to me because it would be blindingly(!) obvious who complained. I have concerns over the fall-out.
All, many thanks for the tea and sympathy, and I don’t feel quite so despondent hearing the shared experiences.
Paul A – I’ve come independently to the same conclusion – the Met Office has become useless at forecasting a clear night. It wasn’t that way not that long ago. I have decided when they say clear, they mean the cloud is thin enough to be be able to make out the phase of the Moon. I will try out some of the other sources, Satellite 24 etc. Thank you for the pointers.
I suspect there is particular geographic problem at work here. With more moisture in the air the Straits of Dover seem to hang on to cloud more than they did, and the prevailing SE winds drag it on to the land.
Alex P – love the term ‘photon torpedo’ applied to domestic lighting. My next door neighbour to the SW is half a mile away but the lights on his daughter’s horse paddock illuminate my lounge! Thankfully they aren’t used too often, and earlier, not later. Everything you say matches my experience here. I’ve tried asking for lights to be adjusted etc but no-one gives a damn. And of course the extra moisture in the air exascerbates the stray light.
Cheers, Alan.
Much appreciated Folks, that’s all most helpful. Certainly Stellarium seemed the most promising (least worst?) of the 3 packages I tried initially. I spent a half-day on it yesterday trawling through the 420-page instruction manual and so far I’ve moved the output to about half-way to where I’d like it. I found the planetary satellite displays you mentioned, I can see that being useful. It would be good to keep Megastar going if possible so I’ll try Emil’s dowload, and check out the Aladin link too. Much appreciated. Alan.
S&T didn’t worry about making a political statement when they took a cheap shot (Dec 2020 p21) at Patrick Moore. They criticised Patrick’s politcal and social opinions which were not especially unusual for his time. I felt this was not simply a failure by the author but a full editorial failure. If the author could not write the article without denigration then it should not have been written at all. I doubt they would have attacked a living person or an American citizen in this way. I wrote to S&T but received no response. Much later they printed (Apr 2021 p6) a letter from a British Columbia reader which did little more than merely note the aberration. This wasn’t sufficient retraction in my book and so they have lost a 25-year subscriber. For these reasons I counsel all of you to shun S&T.
I used 3M 4200 marine adhesive sealant when I set up the 3.5m dome (see small ads in the back of JBAA Dec 2019). This was at the recommendation of the dome manufacturer – Sirius in Australia. Get it from some chandlers. The bottom edge of the GRP panels was abraded a little with wet ‘n’ dry to key the surface. I did the work in Sept 2020 and so far it has kept the water out. I got through three tubes of the stuff. However I fear your joint may now be contaminated with mastic, window sealant etc; you will surely need to remove all traces from both the GRP walls and the concrete before using the 3M product or it will be good money after bad,
Having extracted more than 40 famous astronomers from the memory but still left with gaps, the penny finally dropped last night. I am looking forward to reading a paper in a future Journal detailing the previously unknown astronomical works of Messrs Alkali Stone, Ten Elite Brains, Harry Can Find Me and Crime Or Fine. Aside from that, many thanks to the contributors for an excellent selection of brain teasers. I am attempting it without any research, just staring at questions and worrying them to death. Just the job for those of us suddenly in Tier Alcatraz.
Thanks Dominic, with your pointers and a couple of sessions with a wet towel I’ve got up to speed with how it all works. It’s a bit of an eye-opener to discover that the format of these 2-line-elements harks back to the 80-line punched cards of the 1960’s including only two digits for the year!
He’s used a Baader 8.5nm CCD narrow band filter. The graph shows it is fairly transparent beyond 1,050nm.
Alan
Many thanks folks, I’ll pass those comment back no and let you know what flows from that.
Sorry about all the rubbish lines in my first post. I don’t know why it’s done that.
Alan
Quoting from ‘The Modern Moon’ by Charles Wood, page 93 “Surprisingly not much changes until the impact angle is less than 45 degrees (measured from horizontal). But at shallower angles the crater become increasingly elongated in the direction of projectile travel, and portions of the projectile ricochet and gouge out a series of small pits downrange from the main crater. As the impact angle decreases the ejecta and rays undergo even more pronounced changes than the craters do. When impact angle is less than 15 degrees the ejecta pattern becomes elongated in the downrange direction and a ‘forbidden zone’, where no ejecta appears, develops in the uprange direction. For grazing impacts of just a few degrees the rays go sideways only, producing a butterfly wing pattern. Amazingly, examples of all these exotic ejecta patterns can be found on the Moon, Mars, and Venus. Thus, the asymmetric Proclus ejecta and rays were formed by an oblique impact. … Palus Somni is simply the ray-excluded zone of the Proclus oblique impact.”
On page 94 he goes on to explain how Messier & Messier A were formed by a grazing impact in the range 1 to 5 degrees by a projectile coming from the east. Messier is very elongated, 14 x 6 km. He continues “Bigger craters formed obliquely too, look at the ray patterns of Proclus, Kepler & Tycho. Mare Crisium is simply a larger version of Proclus and Messier. The basin’s elongated shape, low rims on the east and west, and butterfly-wing-like distribution of ejecta to the north and south are all consistent with the low angel impact of an asteroid or comet approaching from the west.” (n.b. Crisium is longer EW than NS, it doesn’t look that way to us because of limb foreshortening.)
Setting up in the garden at 9.30pm yesterday, glancing up I was taken aback to see half a dozen bright lights overhead, sweeping west to east in follow-my-leader order at 20 degree separation. And they kept coming. I lost count. Their track was from Procyon, between Leo & Leo Minor, and away through Bootes. Ten minutes later they were still coming. Every light was brighter than any of the seven stars of the Plough. To think once we made a big thing of seeing the old Echo balloon satellite. Dear o dear, human’s ability to screw things up in innovative new ways knows no limit. It’s just as well we get old and die.
Good to see the scale of the reduction in the hard data from the meteor cameras noted above. I just tried Flightradar24 but there’s something amiss, the map appears but no aircraft at all, yet I can hear one overhead. Maybe the site is swamped by the at-home cautionary-quarantiners looking for amusement.
Hi Peter, the jet in M87 is number 152 in the Arp Atlas of Peculiar Galaxies. I’ve tried for it several times with not a sniff of success. I’m using a 50cm f4.1 dob. There is no drive so in practice my highest usable magnification is x415. In Howard’s article he’s talking about x600 to x700. In the Kanipe/Webb book about the Arp objects, on p303 it cites an observation by the late Barbara Wilson (of AINTNO 100 fame) also using a 20-inch f4, at x340 and x410. She noted “Jet visible running out of core. Difficult. Requires excellent seeing and transparent skies.” This comes back to Owen’s point – the American’s have a much easier time of it. In the Arizona desert and Bryce Canyon in Utah with the unaided eye I’ve seen mag 6 stars as they clear the horizon. At home here, I’m lucky to see anything below Epsilon CMa even when it’s near culmination! Try for the jet on one of those rare nights when anything seems possible.
Alan
I appreciate your take on this Paul. Our different interpretations are certainly a measure of how the appearance of the ground changes hugely with the angle of the Sun. What I’ve done now is transfer my sketch to tracing paper so I can better test the match-up with my downloaded NASA Moon and with your screenshot. If I anchor the sketch at Anaxagoras and adjust the scale to match up the “dark floored crater” with Scoresby, it pushes the limb to the wrong place and the wrong angle. The east end of the “dark feature” is pushed off the disk. Conversely if I scale to match that squashed figure-8 in the sketch to Challis & Main then the limb is spot on. But that leaves me wondering why I didn’t note anything of Scoresby. On the both the virtual Moon and the old-school Hatfield Photographic Atlas it’s a prominent feature! Sun angle again I guess. Your interpretation has the merit of explaining more of the small bright patches.
The tracing paper overlay also suggests the E end of the “dark feature” is due to the crater de Sitter at 80 degrees N but the match is not convincing. Now better informed, I think I need to look out for the next favourable libration and have another go.
