andrew s

Just one thought if the worm is bottoming in the wheel slots the you will never be able to get both edges (driving and non driving) of the worm in contact with the wheel slots at the same time. So however rigid you make it can't remove the backlash. I say this as one who fought the Fullerscope Mk IV long and hard. Regards Andrew

N is sometimes used for carbon stars. Regards Andrew

Yes Regards Andrew

Ok so Stellar Spectral Classification by Gray and Corbally has the following classes O, B, A, F, G, K, M, L, T and WR as the main classes. There are subclasses for S and Carbon stars. There is also OB which is not synonymous with O and B but I have never fully understood it. I have never come across W or H. Maybe W is for white dwarfs but are they stars? In addition there are the luminosity classes II, III, IV, V which are the big lumps on the H-R diagram. Then lots of extra bits for emission stars e, etc etc. Normal star are generally taken as OBAFGKM in classes II to V. Regards Andrew

I am no expert but your wheel "slots" look very shallow compared to those on my Paramount and previous Paralax mount. I do wonder just how many are engaging at any one time. I am sure @Peter Drew will know more than I. Regards Andrew

For the spectral sequence we have Oh Be A Fine Girl Kiss Me Regards Andrew

Good luck with the modifications. I had some 12" Byers gears on a Parallax mount. They were just so good until the observatory burnt down. I don't think their bling caused it. Regards Andrew

I had Kilopoise on a Fullerscope's Mk IV mount it was so viscous it took a month to balance it and only then in the summer. Regards Andrew

Time to give Edward R Byers Co a visit http://www.edbyersco.com/in_stock.html Regards Andrew

Thanks @JeremyS I read the synopsis this morning but not read the whole paper yet. It does look like their interpretation has weakened with the requirement now for order of magnitude variations in concentration with time. Algal blooms perhaps? Regards Andrew

There have been efforts to make synthetic galaxies images from star spectra. They are generally quite dull as are the Wray images. An example browsable gallery is here https://www.illustris-project.org/galaxy_obs/gallery/ Scroll down a few pages and you get some with blue star forming regions. Regards Andrew

The V filter in UBV cuts off before the Halpha line which explains the lack of it in the Wray picture. Regards Andrew

Here is an image of M51 from Wray's book Regards Andrew

I enjoyed watching the moon landings and all the robotic missions before and since then. For me, at least, the lesson from them is why send people into space when robots can do a better job? I know Hubble needed repairing but many space telescope worked well beyond their scheduled life without repair in space. Regards Andrew

@vlaiv this provides a good review . I will still try to find the original filter specs for amusement. Bessel2005ARAA43p293.pdf Regards Andrew PS see table1 in this low_cost_BVRI_filters.pdf

@vlaiv they were once well defined. I will see if I can find the original spec. It certainly involved a particular photomultiplier tube and if I remember correctly involved it's cutoff in U! Regards Andrew Just checked V was cutoff at long wavelength by the PM tube and U by the atmosphere. Still looking for an accessible reference but it looks like issue of consistency stated very early after it's introduction in the 1950s

I have a copy of James D Wray's "The Color Atlas of Galaxies ". Unfortunately, it does not include M31. It does however, very carefully ensure that the images are accurate on the UBV photometric system. While this if different from RGB it is interestin that most of the images are considerably more muted than typically presented images. I am sure they would be considered too dull if posted nowadays. I will try to get an image to post taken in daylight as trying with led .ight fails to reproduce the colour balance. Regards Andrew

Chain saw! What's wrong with you teeth beaver style. 🤓 Regards Andrew

Disconnecting from nature is what has driven our technological progress. The excess of past generations becomes the norm for later. In my youth we had a single heated room now central heating and air conditioning is common. We had one electric appliance (a radio) apart from lighting now I would not dare to count but the two of us have 3 laptops, one desktop, 3 tablets and two smartphones 😁. Regards Andrew

Ask that the wood is put to use. As a hard wood it had uses in interiors but lacks durability externally. This way the CO2 release will be long delayed. Regards Andrew

Yes, same with us spectrocopists mono is a given. Don't fancy E2V prices though! Regards Andrew

As I understand it @Aramcheck burglars quite like security lighting as it let's them see what their doing. On the upside they tend not to eat you. Regards Andrew

For modern man night holds few fears (at least for us on SGL) but for our ancestors night was to be feared as they were pray to a number of night hunters. The desire to have a safe haven with fire and light was probably encoded in our behaviour then which persists to this day. Personally, I enjoy a dark night and wish others did too. Maybe the desire for light at night is a deep connection with an ancient nature not a modern disconnect. Regards Andrew

Science uses coordinate time, just lables on one of the four dimensions of space-time amongst others. There are books on the relationship between the science view of time and our subjective sense of time but no consensus. There is no simple relation. Regards Andrew

They only have rotational symmetry if the collimation is spot on so that the mechanical and optical axis are perfectly aligned. They have to stay that way during any change of angle. If a Newtonian secondary is a little off mechanically (it does not have a unique optic axis and you can slide it in the plane of its reflective surface) you can have perfect optical collimation but the vignetting can be decentred. Regards Andrew