andrew s

Thanks for that but no snow in Castillejar just cloud as far as I can see. Mark you the first two weeks in Jan were fine. Regards Andrew

Indeed he did "exactly" that 😉 although possibly in German. My only prejudice is that I don't have any. Now that's a self referential paradox ala Bertrand Russell. Regards Andrew

Spot on @ollypenrice but it is as well to recall that a spinning, orbiting earth was obviously wrong as we sense no such motion. One man's simplification is another complication. Regards Andrew

I certainly don't know the answer to that. For a mathematician in Newton's era it would have made sense to work through the conic sections looking for a fit. Circle, eclipse, parabola and hyperbola. These were the bread and butter of geometry of that era. Regards Andrew

Simplicity is in the eye of the beholder. It is a judgement of personal taste. Of course, the "best" answer is not always the simplest. QM is based on the second simplest generalised probability theory not the first (classical probability as per rolling dice) Regards Andrew

It cost you the shirt off your back! Regards Andrew

@Lockie you could try an atmospheric dispersion corrector for 10x the cost of the webcam. Regards Andrew

Yes it certainly has attractions especially if you have heavy equipment or a disability. It does add complexity with the Nasmyth mirror and access for collimation and as with all Alt AZ mounts you need a de-rotator for imaging with long exposures. Regards Andrew

In some ways neither is right or wrong. The are just a phemenogical description from different reference frames. Until you add physical content e.g. Newton's gravity or GR it's a matter of choice and even here you can choose different reference frames. Clearly some make the maths simpler than others. Regards Andrew

We might get some early warning (assuming we are still a round) when it starts burning silicon into iron. "Betelgeuse is so close that neutrino detectors might pick up the silicon burning phase, giving us more warning time than the usual neutrino warning system based on supernova neutrinos." Source https://www.physicsforums.com/threads/betelgeuse-unusual-dimming-ready-to-supernova.982440/ I think the consensus is it is still well into the future on human time scales. Regards Andrew

There are some on the BAA website under the discussion topic "Betelgeuse " Regards Andrew

Not really. A faint object in L is the same as one of a similar luminosity in H alpha. It's just photons per second at the detector. Obviously lower rate takes longer to get the shot noise below the read noise.

You could do any option. Prime, Barlow or eyepiece projection with or without filters. There are cheaper £250 low light video cameras. Regards Andrew

Photons are photons it matters not in this case if wide or narrow band as long as the photon creates a single photo electron, which is the case here QE not withstanding. Regards Andrew

You don't need to go that extreme why not a Watec 910HX for £500. Regards Andrew

I had the same initial thoughts but then we all enjoy this hobby for different reasons and in different ways. You pays your money and takes your choice. Regards Andrew

A Cheshire does not need to be square on to the optic axis to work as it has a "rough" reflective surface. I collimated a dublet refractor using a Cheshire eyepiece and aimed for concentric reflections. Yours look out to me. Regards Andrew

Life is full of annoying constraints. However, I don't see any way camara angle can impact field rotation. Framing yes rotation no. I rotate my camera/spectrograph to avoid overlapping spectra with other stars. The orientation stays fixed all night with an eq mount but for the 180 deg turn on the meridian flip which I take out with the rotator. Regards Andrew

In the past I have increased the spacing on filter wheels with thin spacers and once even 10mm. I found it quite stable. I used black masking tape to light seal the gap. I seems to recal the SA200 is thinner than the 100. I needed to align a SW100 with a 200 in a filter wheel. I used a small laser to define a plane by projecting if throught the 200. Them selected the 100 which had glue on the threads and rotated it to match and then left it for the glue to dry. My wife has still not spotted the small marks on the wall paper marking the plane! Regards Andrew PS these days you could 3d print a thin gasket.

Can you remind me what that myth is again @ollypenrice. Regards Andrew

It is not just chromatic aberration that can be reduced but all the seidel aberrations can be reduced/optimised. E.g distortion, coma and field curvature. Regards Andrew

In theory the more glass types and free surfaces (air spaced 2 v cemented 1) the more options the optician has to reduce the aberrations. However, the more glass the longer the cooldown time and the more complex the cell and alignment. It often comes down to the final design and especially the execution. Regards Andrew

I am sure the correlation between astro and PPL is a selection effect due to @ollypenrice location. I will test this at my Astro Soc agm by asking how many members have PPLs. I predict using Bassian statistic the answer will be zero. This is using myself as the prior! Regards Andrew

An off the wall idea. If you have a SX AO unit and an off or on axis guider you could use one on eack scope. As long as the flexure was within the range of the AO unit it would not need to bump the mount and the two would work independently. Ok in theory but I doubt it is practical. Regards Andrew

That will be a Newtonian reflector then. Regards Andrew