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About jnb

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  1. I have acquired an old brass telescope; age unknown, manufacturer unknown. It's a 9cm refractor, approximately F12 - F15 (condition is too poor to be certain as yet). The objective is filthy, inside and out so I need to open up the lens cell to extract, clean and reinstall the lens. A bit of context. This came from someone who had the box and tripod sitting in a garage for years and they know nothing of it's provenance. The box for the scope is rotten and rusted. The scope itself is corroded (not just patina but actual corrosion), the eyepieces are in reasonable condition but the objective is close to opaque. I have cleaned off the front surface of the lens but most of the grime seems to be on the inner surface, confirmed with a checking the scope from the inside with an endoscope. Looking at the inside with the endoscope showed no obvious joints where it should disassemble. Stripping and cleaning the focus with a wire wheel on a dremel and some patience has the mechanics moving again but the lens cell remains the problem. A couple of images to show what I have. The lens cell as is the way of these things has multiple grooves and ridges some of which may be joints most of which are probably decorative. There is a knurled ridge around the front of the scope at the front of the very first ring which suggests it may unscrew but if that has been sitting there for decades it may be difficult to remove and as the first ring is only a few mm deep there's not a lot to grab hold of. I have cleaned it a little (and yes I know about people's opinions on whether you should or shouldn't clean old telescopes but I don't know how old this is and without doing a little cleaning I can't see where I might get into this.) BTW that image is the cleaned condition. Yes that is the "clean" lens! So how might I open that lens cell? Suprisingly enough with a lens in there I don't want to put it in a vice and twist
  2. Apart from a few showers this morning which might make the ground damp for pitching tents it's looking very good.
  3. I've just checked the forecast for the next weekend and it's looking good and clear so I think I'll be camping there this year. If the weather is good it's always one of the better sites for a camping astro weekend; not many sites can offer a historic observatory and castle in addition to the astronomy!
  4. Haven't got the data to hand but a quick back of envelope calculation suggests that the crab nebula is about 10 times the distance so it would take about a century to reach the same apparent size. ( crab nebula is 6500 ly distant and was seen to gov nova in 1054, Betelgeuse is about 650 ly distant)
  5. I should clarify that. I'm talking about diffuse nebulae that are collapsing to form stars and not planetary or SN remnants. They by their nature gave to be stellar masses so are easy to estimate.
  6. I've been sitting here and working out some numbers for the stability of nebulae and how they collapse (the sort of thing that I do while on holiday) and I can model the collapse, ir radiation, and fragmentation of a nebula but does anyone have any figures for 'typical' nebulae sizes and masses?
  7. That might account for her followup question which was could we see it from the observatory.
  8. At the observatory today I picked up a phone call from a woman who had been having, as she put it, a heated argument with her friends over the timing of the new moon because they all wanted to know when ramadam was going to end. the only thing is that while I could tell her the exact time of the new moon I'm sure there is something to do with it not being the moment of new moon but when it is visible. So she went away with smugness points for having the time right but had to concede her friends might be right on the visibility. We were both confused over what happens if you don't have a clear horizon but someone else does.
  9. A good event for adults and curry fans in the Sussex region; http://www.the-observatory.org/themed_evenings?scs=1#beer A bar, a brewery, a curry and a little bit of science all in the old Royal Greenwich Observatory site at Herstmonceux
  10. not to space but about space before anybody thinks otherwise ... I'm thinking of going to the states with my son and visiting kennedy while there. Where else would people suggest going on a trip to the states if I was going to visit Kennedy. This isn't likely to happen soon so he'll be 12 by the time we go.
  11. The Observatory Science Centre at Herstmonceux in Sussex It's where Greenwich observatory moved to after they left Greenwich. Science museum, telescopes, open evenings, astro courses a lot of outreach into schools and public groups. Only downside is that noone seems to be able to find it! Being an observatory not surprisingly it is rural and the signposting is appalling http://the-observatory.org Easiest to find if you use the "wrong" postcode. Use BN27 1RX
  12. The observatory domes at Herstmonceux were always intended to look "sad and neglected" from the moment they were built. Part of the rationale of using copper was that the verdigris effect would allow them age and blend into the surrounding countryside. That said professional optical astronomy in the UK is a bit of a non starter these days because even small professional scopes can be run remotely. In the case of Herstmonceux the instruments are mainly of historical interest we now run the site primarily as a science museum and public outreach centre although we do have a plan to bring our 36" Yapp reflector back into use for exoplanet searches. We can do that with photometric and to a lesser extend doppler methods where the image quality is not the primary requirement and serious work can be done even with relatively poor skies.
  13. Yes - exactly as the title says. I was giving a tour of our observatory recently and one of the people on the tour was blind. When I spoke to him he said he had some peripheral vision but otherwise was pretty much 100% blind. In the tour fortunately I had in my pocket a ball and ball bearing that I use to illustrate the comparitive size of sun and jupiter against the scale of the observatory so I had at least one tactile prop. But apart from that what could I have used?
  14. For practicality and scale of the demonstration the object I use is the doorway to the observatory. That gives an object distance of about 5m so a long focal length is needed for the lens.
  15. Roughly how long did that take you to do? What I want is one or more large lenses to demonstrate creating an inverted image on a screen in one of our observatory domes. I'm usually showing this to 30 or so people but with a magnifying glass it's only really practical for a few people to see at a time.
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