michael.h.f.wilkinson

It would never explode in the Tunguska mold, because the moon lacks an atmosphere. Again, the moon lacks an atmosphere, so the impactor would only start heating up at the very moment of impact. It is quite easily imaginable that the impact site will have been heated to incandescence (molten rock tends to do that), and this will take more than a few seconds to cool down. No (nuclear) chain reaction needed (or indeed possible).

The camera used for most of the shots was a modified Canon EOS 550D, with APM 80mm F/6 triplet and 0.8x reducer. The comet was shot with a Canon EOS 80D and Sigma 50-100 mm zoom at 100 mm and F/1.8. The key is gathering many short subs (60 s, as a rule) and adding loads of them together. Of course, fewer, longer subs means far less processing time, and less readout noise, but if you have simple kit, you have to pay for that in processing time.

Whatever effects you try to invoke, there is simply no way fission reactions could take place, let alone fusion. Fission-based nuclear explosion requires very pure nuclear fuel in order to maintain the chain reaction for long enough, plus a means of slowing down the neutrons sufficiently. To create a nuclear explosion based on fusion, the general method is to use a fission bomb as detonator. You need temperatures in the order of tens of millions degrees to get fusion going properly. However, sudden phase changes (like water or ice suddenly turning to steam) can cause devastating explosions. The damage caused by Krakatoa was caused not so much be the initial volcanic eruption, but by millions of tons of seawater streaming into the resulting caldera , hitting red-hot rock, and suddenly turning to steam, sending a tsunami round the world (it was still measurable in the English channel). A comet containing massive amounts of ice, which suddenly turns to vapour will flatten trees quite nicely, and cause severe burns if you are close enough to the explosion Regarding metals: any metals in the comet are likely to be bound in oxides or silicates. The only iron seems to be commonly seen in certain meteorites, but I doubt metallic iron, let alone magnesium would be present in a comet in any significant amounts.

Take a look at what may be done with the humble EQ3 in this thread: I have been having a lot of fun with my second-hand EQ3-2 mount. Sticking to short subs, you can get pretty decent results. Of course, the bigger, stronger mounts make life a lot easier, but with results like these \ I won't complain. Not prize-winners, but not too shabby either.

That is superb! Really lovely detail, especially with Saturn so low in the sky

Maybe a bit redundant as we have various imaging showcase threads, but here is one of my better ones Please click on image for full resolution

The brightness of the GRS varies quite a bit from year to year. Likewise of the equatorial belts. I have seen years where the SEB was almost absent, as shown in an early shot of Jupiter with a Philips TOUCAM 2010 A year later it had bounced back 2011

A telescope opens the door to the biggest science lab in the universe: the universe itself. I have seen the motions of planets and moons under the force of gravity, or planet-sized storms rage on Jupiter, I have seen magnetic storms rage across the surface of our sun, and matter being blown away from the same surface, I have seen stars explode, and their ghostly remnants glow thousands of years after the explosion, I have seen light generated by unimaginable forces as matter got sucked into the vortex of a supermassive black hole, billions of years in the past. No practical demonstration in the classroom can beat that (although seeing our chemistry teaching setting his work bench on fire in class did leave quite an impression (and a lasting scorch mark on the ceiling))

Very nice collection. Cloudy here, alas

One reason I got a Celestron C8 years back (still have it and use it a lot) is that it is quite light and compact, and yet packs an 8" aperture. That hasn't stopped me getting an APM 80mm F/6 triplet which is just brilliant for wide-field viewing, and packs a 5.3 deg FOV with the Nagler 31 T5. With a 2" Amici prism it gives lovely upright, correct image views. It is also my solar workhorse, and a great DSO imaging scope. There is certainly scope for small scopes.

Beautiful collection. The second seems to be ever so slightly out of focus, but the rest are superb. Have you considered making a mosaic?

In my experience, for planetary and lunar imaging a big SCT will beat a smaller refractor. Aperture is king in lucky imaging. I don't believe a TSA120 or TS115 will be able to get a Jupiter image like the best one I got from my Celestron C8 I have at times even resolved albedo spots on Ganymede. Your Mewlon would give the C8 a serious run for its money, but a 4" or 5" refractor? I doubt it. Damian Peach seems to be happy with big SCTs, so I will stick with my big aperture approach.

Absolutely. Really nice and sharp.

For planetary imaging, I use an SCT (Celestron C8), which holds collimation extremely well. A refractor of similar resolution would cost the earth (much more than a bigger SCT). I might well go for a C11 or even C14, but refractors in that aperture range are beyond my wallet

Great images. The Mewlon has the edge, I would say

Very nice collection

Nice result. I lack a spectrograph, but inserting a UHC filter into the optical path can make the nova seem to brighten with respect to the other stars quite distinctly, indicating that the spectrum is dominated by emission lines. I did this for Nova 2013 Del, and you could really see a shift from continuum to line emission

For purely solar imaging, I wonder if a triplet is really needed, or even ED glass. I image the sun quite a bit, and for H-alpha and Ca-K at 0.3 Å and 2.4 Å respectively, CA correction is totally unnecessary. Even in the solar continuum band, very little CA can be noticed. Spherical aberration is probably more important, as is sheer aperture (although seeing in Ca-K can spoil matters above 4" aperture). Of course, an apo scope is a better all-round imaging

FPL 51 combined with a Lanthanum glass element

No sharpening applied, just blurring and resampling of the high-res image. That was probably contrast stretched. The dark colour you added to the simulated image muddies the comparison. My original image was taken at 540 nm, slightly deconvolved and sharpened, but no real contrast stretch. I will run our connected granulometry software on this and see if the morphological pattern spectra are similar, that should allow assessment of the similarity of the textures in a quantitative way. I think we agree that the granulation is visible at 80 mm aperture, but that the shapes of the grains themselves are not well resolved.

But then I mage at roughly 0.5" per pixel and get this Which is pretty close to the texture I see in the image I took. (I added blur, incidentally)

I also see a sharper image than what vlaiv posted as representative of the view of an 80mm. The main issue here is that I am not sure his image reproduces the dynamic range of the live image that well. The input image has been processed, and might not represent contrast faithfully. Higher contrast always results in higher apparent resolution.

What I mean is that in an 80 mm scope, the smallest convection cells are not necessarily accurately imaged, because they are blurred by a point-spread function that somewhat bigger than their extent. I can distinguish the individual cells, and the bigger ones definitely stand out clearly. A four inch scope would show this a lot better. The problem with language is that the world "resolved" can be interpreted differently. Are the individual grains resolved by an 80 mm scope? According to the Rayleigh criterion they are. Can we accurately resolve the sizes and shapes of 2" grains with a 2" radius of the Airy disc? Not really.

The final statement implies that an 80mm scope can see granulation, as the centroids of the convection cells are (at least) 2" apart, and the Rayleigh criterion for resolution at 540 nm (solar continuum band) is 1.7". The individual cells are not really resolved in terms of their shapes or sizes, just like none of our scopes can show a resolved image of any star apart from the sun. However, the texture is quite easily seen.

Took some quick shots with the Sigma 150-600 mm zoom and Canon EOS 80D. Stacked 36 frames in AS!3. This is a slight crop Not too bad for a quick shot using a monopod