Astrobits

I was thinking that the optics might be incomplete and should have a transfer lens as Andrew suggested. Alternatively, there might have been plans for a very large field sensor at the focus you have identified. As regards the design of a Cass, the secondary is not just reflecting the cone of light but is also amplyfing the focal length by a certain factor ( like a barlow ). Thus moving the secondary by 10" will move the focal point 10 x the amplification factor. Most Cass designs have an amplification factor of around 4x or 5x so you might not need to move the secondary more than 2"-3" However, the design of Cass optics ties the separation of the mirrors and their curves together so it might not perform quite as well as the original specs. As you don't have the option of using it as is you will just have to try something and see what you get. Nigel

O.K. Mandy has it. Here's the plot with data . The problem is that a proper scientific experiment to verify a hypothesis would involve more than one Earth and the ability to vary the CO2 at will without changing other factors. After over 100 years we are still testing Einstein's General Relativity theory, so why are we so sure that the CO2 theory is perfect? I read the third assessment report of the IPCC. The conclusion they reached was an average of approx 13 different climate models. There were more than 13 available ( and non of them included ALL the possible variables---as admitted in the report) so why choose those 13? It doesn't say. I have a talk regarding climate and the external factors which can affect it which I can give to any club that is interested and that is within reasonable driving distance for me here in Somerset, For the record, I believe that the climate IS changing and we should reduce our CO2 emissions by burning less fossil fuel. After all, fossil fuel stocks ARE limited and WILL run out eventually and it would be best to use them for other uses for which they are more suited than simply burning them. Nigel

I offer this graph for your perusal: Anything familiar about it? I have removed the Y axis data just to keep you guessing, the X axis is date ( years). Nigel

Many years ago I was shown a small mirror produced by an overseas company. Reflections in that mirror were all surrounded by a nice coloured halo. No, it wasn't back silvered, it had an exceptionally thick overcoat!!!!!!!!!!! Nigel

I have just opened up my 16" which has been in storage for the past few years ( due to observatory damage, I really must get round to re-building it ) and taken a pic of the mirror. 22+ years and counting: Nigel

Hi David, A couple of points for interest sake. As far as I am aware, all mirrors are overcoated with Silicon Dioxide ( silica) ( normal ) or multi-layer ( enhanced reflectivity ) except those professional telescopes used for spectroscopy and unless the owner has specifically asked for a plain Al surface. The silica can interfere with spectra, adding it's own fingerprint, so not using it is preferable/mandatory in the professional world. Certainly the mirrors in amateur telescopes that I am aware of over the last 50+ years have had an overcoating of one sort or another. Although it is usual to quote that mirrors have a silica overcoat, it is not possible to evaporate silica directly in most coating chambers. Therefore Silicon Monoxide is evaporated onto the mirror and this will slowly oxidise to Silicon Dioxide over the following days on exposure to air. The coaters that I used back in the 90's always waited a day before packaging up mirrors to allow the surface to harden a bit. Overcoated mirrors will last many years provided they have a tight fitting lid when not in use. My own 16" has the original coating from the time that I made it about 22 years ago, and it is still perfectly useable. Nigel

If you simply drop the "James" then the WEBB TELESCOPE could honour any Webb you choose. For me it would be the Rev T.W.WEBB (Celestial Objects for Common Telescopes). Nigel

I have a pair of the 10 x 30's that I used during the 1999 Leonid meteor watch so they are at least 23 years old and still going. I had a problem with leakey batteries which damaged the terminals but I managed to clean them up and they have been going fine since. I also have a pair of the 15 x 50's which are over 20 years old now and are my main goto bins. Never had a problem with them. Nigel

As I mentioned in Nigella's post on Sun Dogs, here is a photo I took about 25 years ago just to the south of Bath. It is on slide film and I have copied it with my DSLR. It shows both Sun Dogs an well as the Solar Halo, Sun Pillar and Circumzenithal (?) arc. Nigel

I did wonder if the IAU had that name. Nigel

Nicely seen Nigella. I think that they are more common than you might think. I have seen them a fair number of times. There are also many other phenomena of a similar kind to be seen with the right conditions. I won't usurp your thread with the pic that I got many years ago, I might post it later on a separate thread. Nigel

According to Wikipedia Gamma Velorum is also called Regor: https://simple.wikipedia.org/wiki/Gamma_Velorum Nigel

I was in Southern Portugal for the Leonids. It was one of the few places in Europe that was clear that night. The storm started about 1am and lasted for less than 2 hours although there were stragglers outside those times. (The start also coincided with the rising of the radiant so the first few meteors were VERY long). I videoed them but, of course the video camera only recorded the brightest ones. An edited version is up on youtube. Ignore the time on the video, I forgot to correct it. On youtube look for Leonids 1999. Nigel

Well, I guess that I have been really lucky as I consider that I have seen all three options. Comets West in 1975/6, Comet Hale-Bopp 1995, McNaught 2006, Lovejoy 2011. Meteor shower - Leonids in 1999 at about 5000/hr. Supernova 1987 that I estimated at the time reached mag 2.8. Admittedly, these can be improved upon but I was just lucky to be living in the right hemispheres at the right times for these. Nigel

Didn't take long to get the hang of this prog. The only drawback is that it was intended to be printed large onto paper and then reduced photographically using high definition transparency film. Now I don't have a working film camera any more, having gone digital, and therefore I cannot use this unless I purchase some very clear transparency film and print it direct with an inkjet printer. The question is: is printer transparency film of sufficient optical quality for this purpose and can my printer print accurately enough? I don't know the answers. Here's a screengrab of the prog in action: Nigel

Yes, I have downloaded it and now have this programme running in Ubuntu 20.04 thanks to my computer guru son. Still have to read how to use it but other tasks await my attention at the moment. Nigel

That has always been my objection to the Ronchi test, trying to compare curves. The InvRonchi sounds like a useful solution. Nigel

There are actually three crosses that should be visible to you in the southern skies. The most obvious is the the Southern Cross that I guess is the one you have seen. Not far away is the Diamond Cross and a bit further is the False Cross. The Diamond Cross will be the most difficult as it is the furthest south and the faintest but will clear a zero degree horizon at 17 deg N latitude by a few degrees. Look them up. Nigel

Try Sutherland, South Africa. About 3 hours drive from Cape Town and in the middle of the Karoo. There are some b & b's that have telescopes for guests and the South African Astronomical Observatory is a short drive away. There are many telescopes there including SALT ( Southern African Large Telescope) 11M of Hexagonal mirrors. They also do guided tours and observation evenings if you choose the right times ( although I don't know how Covid has interrupted these arrangements). Nigel

Men's Sheds do vary a lot. My local, of which I am a member, has just about every common tool for woodwork, some donated ( in various states of condition) and some new stuff purchased via grants. We have just got a new table saw with 12" dia blade ( bigger than most of those often sold for hobbyists ) able to handle full 1220mm x2440mm sheets with ease. Nigel

Agree with all the above comments. If you don't want to purchase more tools go to your local Men's Shed ( there are plenty in West Yorkshire ) who will help you with this project. Every Men's Shed is different and members experience and tools available will vary so try more than one if your first one doesn't have the facilities you require. https://menssheds.org.uk/find-a-shed/ Nigel

Quasar CTA102 at 8 billion light years. Nigel

Expected peak magnitude is around 13-15 so not one for anything but imagers.☹️ Nigel

Many years ago ( mid 80's) I had the opportunity to view through the Innes Telescope in South Africa. This is a 26 1/2" refractor, also made by Grubb and is still operational afaik. It was a group viewing for the Johannesburg Center of ASSA of which I was a member. The telescope was made for observation and measurement of double stars and probably has as much CA as other refractors of the time. The view of Mars was definitely nothing to write home about, many of us were of the opinion that the 6" refractor ( another Grubb one I think) that we used regularly just a short walk up the hill provided just as good a view. Nigel

As above, both will be unwieldy to put onto an equatorial mount. However, I am always surprised to see no/little mention of sub-aperture masks on a big 'scope when the seeing does not favour the full aperture on planetary detail. Way back in the mid-80's I observed a particularly close opposition of Mars using three 'scopes on the same equatorial mounting and I could switch between them in seconds. The three 'scopes were: 6" Cooke refractor, 7" refractor ( I can't remember the make ) and a 12" Tinsley Laboratories Cassegrainian. The best view of detail on Mars was with the 6", the other two providing somewhat less pleasing images. So, Go for the 12" and try sub-aperture ( and off axis ) masks to see if the view is improved on those less-than-good nights. And when you want deep sky you'll have that extra aperture. Nigel