michael.h.f.wilkinson

I agree, all formulations I can recall had problems (hence the can of worms), but it is always difficult to rule out MOND completely (especially with some sprinkling of DM)

MOND opens an entirely different can of worms. Hasn't been ruled out yet, however

That's what's makes science such fun

So what is my 105 mm diameter protection filter in front of my 150-600 mm zoom made of? Optically flat glass is not that hard to make (check out the Edmund Optics Catalogue) The original Schmidt corrector plates were made by pulling a partial vacuum beneath a suitably supported glass plate, and polishing it flat, so after release of the pressure the surface had the suitable curved shape (from my MSc course in optical astronomy at the Kapteyn Astronomical Institute). A colleague over at Space Research across the road can confirm this (he makes optics for research instruments for a living) Other examples are Baader ERF for H-alpha use: huge diameters do not cost the earth (their high price mainly being down to the coatings, not the flat optical surface)

This perpetuates a recurring myth that glass filters are not figured properly optically, because this is somehow far ore difficult than figuring a spherical surface (or even a paraboloid). You are confusing an optical flat used to test the figure of optical components, and has to be flat to within 1/200 lambda typically, with plane-parallel glass needed for filters (where 1/10 lambda is sufficient). The latter are no more expensive than your typical UV/protection filter for camera lenses, or the corrector plate of my SCT (which is actually harder to figure). I do agree that glass solar filters are far too expensive, given the availability of solar film of the same or even superior performance. Glass filters are more durable, as a rule, but then replacing a damaged piece of solar film is so cheap that you could probably replace the filter ten times for the cost of one glass filter.

Agreed. You generally just use the centre, and scan the skies. Still, I have always found field curvature really annoying. And severe infiltration of the outskirts of the FOV by seagulls is also hard to ignore.

I have had these bins, which I primarily want to use for birding, but are a useful lightweight addition for astronomy, for a couple of days, and have been able to put them through their paces for both birding and astronomy (albeit the latter only briefly). As expected, the binoculars are very well made, feeling very solid, without being too heavy. They come with a strap and a sturdy carrying bag, which should protect them well. My two minor gripes with the Nikon Monarch 7 10x42 were (a) the fact that the (very soft) bag had no shoulder strap, only a means of attachment to a belt (which I find uncomfortable), and (b) that the rear lens caps fell off the eyepieces at the drop of a hat. They were secured by a strap, but it was still annoying. With the Zeiss, no such problems. The bag has a detachable, well padded shoulder strap, and the lens caps are secure, and yet easily removed when needed. The views through these binoculars are amazing. It is difficult to spot any chromatic aberration, even along high contrast edges close to the edge of the FOV. The views are very sharp, and focusing is very intuitive, with the image snapping into focus easily. I spent some time over lunch last week following a common tern which was hunting over one of the large ponds on campus, and it easy to keep the wheeling and sometimes suddenly diving bird both in the FOV and in focus. The Nikons seemed to be a touch more sluggish in this respect. I have also been amazed at the wealth of detail visible in the plumage of various birds, even in unfavourable lighting conditions, like strong backlight, or at dusk. I have not had any trouble with glare or internal reflections, or blackouts and kidney beaning. The binoculars show slight pincushion distortion. There is plenty eye relief for use with my glasses. I also had a short spell under clear skies at night, and was very pleased with the views as well. On the whole, stars seem pinpoint across the field, and only if you take a very bright star like Arcturus can you note some astigmatism towards the edge of the FOV (say, the outer 10-15%). There is no trace of field curvature I could make out. In short, I am very pleased indeed with the performance of these binoculars, and would say that these are easily the best birding binoculars I have even looked through. The Helios LightQuest 16x80 do show much fainter objects at night, of course, but for sheer image quality the Zeiss bins are definitely better

Sounds very interesting. I am thinking of getting a RASA 8 one of these days, so I will be watching this with interest.

Lovely collection. Nothing but clouds here, alas

Really lovely, and not often seen on SGL.

Incandescence does not need a catalyst, it just needs heat. The second law of thermodynamics indicates that ultimately, all energy will be converted to heat, so if a heavy object travelling at some tens of km/s is smashed into a stationary object, you will release a lot of heat. If by massive we mean a stone, iron, or even icy object tens or hundreds of meters across at minimum, the heat should be enough to generate photons at visible wavelengths (i.e. enough for incandescence).

You have indeed conditionally collimated the binoculars. Full collimation really requires a proper optical bench, lasers, etc, which is a bit beyond what you can find in your average garden shed

Indeed 😁😁

Just got these as a special treat, and replacement for my beloved Nikon Monarch 7 10x42 mm, which someone strolled off with. Even in today's murky weather the views are astonishingly bright and crisp. They are really light, but sturdy, and beautifully balanced. If nobody strolls off with them, these could last a lifetime

Sounds like collimation is off. If collimation is not perfect, terrestrial targets can often be merged by the brain well enough, although eye strain can set in. With point sources, like stars, the brain equally accepts a double and a single star as valid results. Furthermore, there may be a situation that the collimation is conditionally correct, i.e. the two optical axes are parallel at a particular setting of the inter-pupillary distance (IPD). However, if both optical axes are not parallel to the hinge axis, they will lose collimation if the IPD is changed. This may be the case

ZWO is certainly good value for money. I have only had one cooled camera which I chose mainly based on the fact that it was going cheap second-hand, and matched the colour version I already had in resolution and sensor size. I was originally going to go for an ASI294MM-Pro, but when the offer came up, I jumped on it

I got a modded Canon EOS 550D for just 200 euro, and that gives really nice results. I also tried my ASI183MC planetary and lunar camera for DSOs, which is more sensitive, but has a much smaller sensor I have since moved to a monochrome, cooled camera (ASI183MM-Pro) which is better still. Note, this was just under 2 h of data, so very little to work with There are several cooled cameras within your budget, so you could go for a dedicated astro camera

Possible, we simply don't know

Very nice collection!

I would say some sort of filter housing will be needed. Alternatively, you could get an L-Pro clip filter, which might be the cheaper option

Early days yet, we have yet to get things to work fast enough and acurately enough, all initially on simulated data, as the telescope array isn't ready yet

Dark energy works on the expansion of the bulk of the universe, dark matter locally contracts matter into stars, galaxies, clusters, walls etc, whereas dark energy expands the voids between these structures. We need dark energy to explain the apparent accelleration of the expansion of the universe, but dark matter because the visible matter cannot explain all the structures we see.

There are various theories as to the composition of dark matter. Several propose "new" particles like axions. The were first proposed in 1977 to solve problems in quantum chromodynamics, and given their small energies could be responsible for the dark matter. There are several other options. I am currently involved in designing detection algorithms for the Cherenkov Telescope Array to look for potential candidates by observing gamma rays from potentially dark-matter rich dwarf galaxies. Hopefully, careful observations might solve the mystery

That is really lovely; love the detail in the outer shell. I shot M27 last year with my un-cooled ASI183MC and Meade 6" F/5 Schmidt-Newton, with L-eNhance filter, which worked reasonably well, but this year I should follow your example and use the new ASI183MM-Pro with H-alpha filter to get more of the outer shell (which in my shot shows mainly O-III). Your core is also less blown out

Comets are mostly ice (mainly water, but also amonia, carbondioxide, etc), with some rock and dirt thrown in for good measure. You do not need a large proportion of a sizeable comet to suddenly turn to gaseous state to get a huge explosion. There are various indications that the body may have been a rocky or even iron meteorite some tens of metres across, and models show they too can explode when internal stresses become too great for cohesive forces. This too could cause the object to disintegrate completely. There is a possibility that lake Cheko holds some remnant of course, but there is no need to invoke nuclear explosions when the old-fashioned "smash stuff together with immense force" will do the job of creating massive bangs. Note that neither rocky nor iron asteroids would contain enough hydrogen (let alone deuterium or tritium) for fusion, nor enough fissible material for fission, and certainly not in the purity needed