saac

7 hours ago, Skipper Billy said:

I have used it extensively on wooden boats which flex a LOT and are dipped in and out of sea water - freezing cold then baked in sun - it is very tough stuff.

I painted the south facing wall of our wooden garage with it 11 years ago and it is still perfect. Avoid red if it gets a lot of UK.

Thanks Billy, I'll give it a try, fed up being disappointed by the Deluxe paint and Im ever mindful now of doing work up on the roof - I need something that will last. 

Jim

3 hours ago, Skipper Billy said:

As long as its dry and you remove the loose stuff then 2 coats of 2 pack polyurethane paint should give you 10+ years

https://www.international-yachtpaint.com/en/gb/boat-paint-products/topcoat-finishes/perfection

 

Billy, I take it that is a specialist marine paint (high performance).  Would you recommend it for non marine applications? My house has dormers in the roof and I've been using Deluxe Weathershield but it does not last any more than 2 years and it peels off. The roof is south facing so it gets a lot of uv incident on it.  I wonder if your International paint would be worth a try ?

Jim

Instead of paint why not oil it.  My obsy (cedar wood throughout walls and roof ) is re-oiled each summer and does the trick , nice and watertight. 

Jim

53 minutes ago, andrew s said:

This paper seems to show it does https://www.arxiv-vanity.com/papers/1405.5540/

To quote "Reionization heats the gas and drives it out of the shallow potential wells of low mass halos, affecting especially those below a sharp mass threshold that corresponds to a virial temperature of ∼2×104 K at zreion. The loss of baryons leads to a sharp decline in the star forming activity of early-collapsing systems, which, compounded by feedback from early star formation, empties halos of gas and leaves behind systems where a single old stellar component prevails."

Regards Andrew

Thanks for the link Andrew; so it tapped the brakes so to speak    I had read that early star formation was aided by the formation of molecular hydrogen which acted to absorb heat giving gravity the leading edge in collapsing the gas clouds.  It's a fascinating subject for sure and relatively accessible but I guess hard won by those who led the way. 

Jim 

1 hour ago, andrew s said:

Simple answer is I don't  know. I will look into my extensive library.  I do know that real data from that era is sparse to say the least.

Regards Andrew 

I picked up "At The Edge of Time - Exploring the Mysteries of Our Universe's First Seconds" by Dan Hooper - I think it was following a review in BBC Sky at Night .  Early days with it but so far I like the way the author doesn't just drop statements as received fact but makes a point to cite evidence.   He has an easy to follow style as well which always helps with this type of subject.  Only covers the first few second though - need to wait for the sequel to find out about stellar formation.  

Jim 

4 minutes ago, andrew s said:

Yes the formation of neutral hydrogen let the CMB fee but it was sometime later that stars formed and their UV re-ionized the hydrogen.

Regards  Andrew 

So did re ionisation have any impact on subsequent star formation ?    The Horizon video is no longer available on the BBC iPlayer - odd clips are up on YouTube. It's a shame it was watchable albeit suffering from the  repetitive graphic style of the later Horizon documentaries. 

Jim  

1 hour ago, andrew s said:

I thought star formation re-inonised the Universe. The formation of neutral hydrogen released the CMB photons. However, it happened at a lower temperature than the ionization temperature of hydrogen due to the long tail in the Boltzman temperature distribution. 

I may well be wrong so will check.

Regards 

I thought that the CMB photons were able to travel unchecked before star formation - the thinning of the fog until it became transparent. Didn't stellar formation then follow ? There was a useful Horizon documentary o this called Cosmic Dawn . I'll see if I can find a link. 

Jim 

3 minutes ago, maw lod qan said:

I think what it must have been like, before The Big Bang.

Nothing, void, darkness.

Then from that nothing, it happened and there was light.

And we all know without a doubt that when we look up into a cloudless night sky, it is good!

That's the executive summary  

Jim 

39 minutes ago, Corncrake said:

Thanks for the link and tabulation.

I hadn't previously paid attention to just how long after f -last scattering till g -the first stars turned on, I knew it was a while ! but 1000million years is well, .,! almost as boggling to the brain cell as the Planck time(length)

Thinks > must google what was going on during that time*, did it take that long for the small fluctuations in the bang to clump everything into big lumps I suppose.

 

* what were Tom&Jerry doing all that time   sorry couldn't resist.

I'n no authority but I wonder if the newly forming nuclei still had sufficient kinetic energy  - due to the temperature 3000K (f) - that gravity would not yet dominate. Once things cooled, gravity would start to pull hydrogen together. I believe the electromagnetic force also had a significant role to play in clumping of matter as well.  In our macro world we would look for nucleation sites which encourage matter to accumulate  - such as evident in formation of snow flakes where microscopic pieces of dirt  provide a site  for the crystals to coalesce.    I wonder if there was some similar mechanism -  perturbations in fields or temperature gradients which encouraged matter to clump leading to star formation.  The period of the "cosmic dark age"  - time before the universe would even become transparent to allow transmission of light - free electrons interacting and "soaking up" any potential roaming photons is another fascinating period. 

Jim 

I love contemplating the event in the timeline called "cosmic dawn". The moment the first stars switched on and light permeated the universe as it became transparent - electrons having lost sufficient energy (temperature had cooled enough) to be bound to the nuclei allowing photons to spread across the heavens.  I think of myself parked up at a safe distance in the Starship enterprise (humour me) watching and waiting for that first star to light up - wow what that would have been like - yet nothing there to see it or recognise that it had happened. The only signpost written in the Big Bang Theory waiting for Lemaitre to tell the story.    Such are the sights that will forever be denied to our eyes. 

Jim 

40 minutes ago, teoria_del_big_bang said:

I wish I had never looked at this thread. I have many times ponder similar questions and every time my head almost explodes.  My brain is just not capable of comprehending any of this.

Steve

Steve, here's a summary of the timeline - it's fascinating stuff alright.  Source  http://physics.weber.edu/carroll/honors-time/cosmology.htm

On 31/05/2020 at 15:39, Ags said:

I don't know about your zebra, but I'm currently unable to prove there is still a mouse in my kitchen.

Remember that the mouse is just a wave of probability, a disturbance in the electromouse field - a weekly interacting field and generally localised. You certainly cannot know both its position and its momentum -  the mouse would collapse if you did - this generally happens when the electromouse field interacts with the cheese boson   

 Jim 

4 minutes ago, Davey-T said:

Cap'n Kirk never had these problems 😁

Dave

"Punch it"   

I'm "in waiting" , after seeing what can be done with NV equipment especially white phosphorus I can't wait. Or rather I am waiting, I need to wait  for prices to reach what I would consider attainable.

Jim 

As much as I am a massive fan of Polemaster I had problems with it the other week - software I think.  The camera didn't seem to upload quickly enough so the image in the viewing window on the screen lagged any movement of the camera.  I ended up switching to Sharpcap to do the polar alignment still using the Polemaster supplied camera - so it wasn't a hardware issue as teh camera itself worked fine. I have a feeling that I may just need to update to the latest driver , I hope so as I really liked how Polemaster worked 

Jim 

11 minutes ago, Thalestris24 said:

I think you have to reinstall it every time Autocad does an update...

Louise

That would make sense Louise , it went through an update for me last month - ouch that's a wee bit annoying then but it is worth it. 

Jim 

On 09/05/2020 at 20:58, Paul Gerlach said:

Jim,

Source files of the LOWSPEC 2 and 3 can be found on Thingiverse:

https://www.thingiverse.com/thing:2455390/files

Paul

Paul, sorry I should have looked there first, I forgot you had already provided the source files, thanks.  I made an extension block to the focuser railholder (b block) to give the micrometer a little more support, again held by an interference fit.  In truth my micrometer head is perhaps a little too big,  a smaller one similar may have been more suitable.  I'll post a photograph up later.  

On 22/05/2020 at 11:06, Jagho said:

Jim or @Paul Gerlach, could you show the link I can download this plugin from, please?

 

Edit: OK. I've found it. 

Hi Jagho, here's the instructions Paul posted - it was either on this thread or the 3D printer , I tried finding the original post but I couldn't locate it. Anyway  I copied the original instructions onto a word document.  It worked a treat when I installed it but some reason Fusion is no longer accessing it for me so I'll have to go through it again. 

ps - and here's Paul's original thread  - I think you need it for the file instructions ,     

Read Me - Fusion Autocad Threads.docx

Thinks of Edge of Darkness lol - anybody remember that ?

1 minute ago, Alien 13 said:

Looked but couldn't find the circuit diagram, have loads of sources like Talumar lenses old military compasses and a block of plutonium somewhere..

Alan

Step away from the dull  strangely warm metal Alan. 

Jim 

Balls of household dust apparently I think is also an emitter I believe it harbours radon gas . Where would you get uranium glass ?

Chris that is really cool, ordering parts tomorrow    Need to think about suitable and readily available sources - need to be safe for school use.  Thanks for sharing this  

Jim 

4 minutes ago, Jennifer91 said:

I can't see anything

I adore astrology and I'm very passionate about it

somebody is bored by the look on their faces  

On 29/04/2020 at 11:04, Paul Gerlach said:

Jim,

Would this not create a lot of force on the micrometer head? Considering you are using two springs. How do you keep the micrometer head in place?
I see you had a lot of warping issues during printing. What material did you use?

Paul

Hi Paul, the spring strength of the springs is not so high as to cause any problem with the micrometer and it does return the lens assembly nicely when backward focusing.  At the moment the barrel of the micrometer is in an interference fit with the hole in rail-holder block. I had to ream out the hole in the rail-holder a little to accept the larger diameter of the micrometer barrel. What I would like to do is re print the rail holder block to accept and secure the micrometer properly, perhaps including a grub screw to secure the micrometer in the block.  The measuring face of the micrometer then simply pushes against the threaded insert inside the other rail-holder block; It all seems to work quite smoothly.  I wonder, and I hope I'm not being too cheeky here but would you be able to provide a copy of the stl file for the rail holder blocks - that would be an easier starting point for me. I understand if your not happy to do this though. 

Yes the base and lid of my print show signs of warping. This was the first long print run I had undertaken and after an initial hiccup on the first run I decided to print it continuously over night - I can't remember exactly how long but it was the best part of 24 hours. I think I the base took too much heat , perhaps I should have broken it down into shorter print runs (my printer allows for interrupts).  The filament I used as PLA; once I have this once shaken down I'm going to print your Low spec 3 version. 

Jim 

Excellent video . Has convinced me to join BAA.

Jim