andrew s

Just to be clear, I am amazed by Andy's skills and all those who produce such stunning images. My comment was just stating a personal preference. Regards Andrew

You could try IRAF but would not recommend it unless you can't find anything else. Regards Andrew

Yes, thanks, I realise how it's done. I used airbrushing in the sense of magazines improving the image of a cover girl or man, removing imperfections, rather than literally. Sorry to have misled you. Regards Andrew

Fine images though I much prefer the one with stars. Air brushing them out seems wrong to me, but I accept it's a personal choice along with much else in astroimagej processing. Regards Andrew

I think there are two elements to what you call reach. Longer focal length to give higher resolution or image scale and aperture to obtain fainter objects. Depending on which or both will impact the choice. Look at the images in the observing section and see what kit is being used to guide you. Regards Andrew

I would tend to agree. I am more cat like than dog like. Regards Andrew

Either that or she was more scared of the cat than devoted to you. We had people complain that our first two neutered male Burmese were chasing their dogs. Regards Andrew

Cats are purr-fect and independant creatures, dogs mere synphopants to human ego. 🐈🐱🐈 Regards Andrew

We had a westie when I was a teenager, a rescue dog much fun. Now a confirmed Burmese cat fan on the 4th pair. Regards Andrew

Not me, unless I was in some way out of my mind. Regards Andrew

Hammer house of horror I belive. Regards Andrew

Cats are far too sensible. Regards Andrew

A frog mouthed Newtonian. Regards Andrew

I was not very impressed with it. I just used it for finding with a video camera!

I am a fatalist and work on the principle that if you can do something about it do it, if not don't worry about it. As I said the insurance paid up and I had fun choosing new kit from scratch. Indeed getting it all at once resulted in a better setup. Regards Andrew

A dehumidifier caught fire. It was the only thing on as I was about to go on holiday. I had to damp the fire down before rushing to the airport. Regards Andrew

No, It was a very hot fire that melted the low spec aluminium alloy and the mirror shattered on impact with the concrete block the steel pier was set in. The pier and the padlock that was on the door was all the survived. Regards Andrew

I have mentioned thus before but my observatory burnt to the ground taking a 12" Newtonian, Tak Sky 90, Parallax mount plus lot more with it. Fortunately, the insurance paid out. Regards Andrew

Excellent talk, now where did I put my sketching kit. Regards Andrew

@Mr Spock is correct, for a compound instrument you work out the effective focal length by projecting back the light cone until its diameter reaches that of the aperture stop. The focal length is the the distance along the optic axis from there to the focus. Obviously this can be well outside the length of the telescope. Regards Andrew PS the effective focal length varies as the main mirror moves to achieve focus.

Your next Doh! Maybe forgetting to remove it 😏. Mine are so frequent they form a peicewise differentiable world line. Regards Andrew

I would imagine it's your height above sea level. It's needed for accurate pointing. Regards Andrew

I wondered why I use it! 🙃 Regards Andrew

I am getting old. I intended to say that section A2 of this , that I posted before, shows the dispersion relation in anisotropic coordinated is equivalent to the isotropic one. It does so by derivation from Maxwell's equations in anisotropic form. As they are equivalent no experiment can differentiate them. However, as the authors point out the equations are symmetric and more elegant in isotropic form. All everyday science adopts the symmetric convention and it is built into the current SI units. Regards Andrew

Not at all. The only claim I am making is that you can't empirically tell them apart. It is because of this Robin's experiment can't prove the isotropy of the one way speed of light. We have for good reason adopted, by convention, the simplest symmetrical solution. You were claiming you could empirically differentiate between them which I hope the papers convinced you you can't. I can transform a Sun centered model of the solar system to an Earth centred one. The equations of motion would be complex and give little or no insight into the dynamics. However, it would be empirically identical to the Sun centered system. You can't prove one is right and one wrong. They are more or less useful in different contexts. If I am felling a tree in my garden the Earth centred system is the one I use. On Newtons laws, the MOND theories are doing exactly what you are claiming is not done. Also the neutrino was predicted to patch up the conservation of energy and momentum long before it was found. One last point might help. No observation is ever theory independent. Making any observation relies on a framework of theory. To a child the Sun obviously transits the earth from the eastern horizon to the western horizon. It is only in a wider theoretical model that you observe otherwise and "see" it is obviously due to the rotation of the earth. Regards Andrew PS it was Newtons theory of gravity that allowed the prediction of the "unseen" planets not the adoption of a Sun centered system which is incidentally only an approximation. It also was, wrongly as it turns out, used in exactly the same way to predict the planet Vulcan to explain the deviation of Mercury's orbit. Science is much more messy than you appear to think it is.