andrew s

@Thalestris24 the slant is most likely due to a tilt of the diffraction grating out of the plane perpendicular to the optic axis. Try adjusting it. Regards Andrew

I always enjoy the repair shop. Just a pleasure to see such skills deployed by such delightful craftsmen and women. The redcoat of the mirror was by Orion Optics. Pity it got dusty but a hazard of a shared workspace. Regards Andrew

They are unpredictable. People have looked for relationships between intensity and the time between flares etc. but none has yet been found. Regards Andrew

High power eyepieces often have a "Barlow" built in but have the advantage is that they are optimised with the rest of the lenses rather than being generic. Regards Andrew

After about 18 hrs (4600 images) of monitoring V833 Tau with no flares I swapped to HIP25953 M4Ve last night with out much expectation as there forecast was for cloud. However, to my surprise it flared. I still have to process the spectra but here is the discovery plot of the intensity of the zero order with time v two comparison stars . Each exposure is 100s through a SA200 grating. I will post the spectra once they are reduced. Regards Andrew Caption date wrong it was the 14th

Don't you need a ladder to get on it on the upper positions? Seriously nice simple well executed design. Regards Andrew

The trick it seems is to forget DPD are coming. They turned up yesterday with a 1Kg tub of optical pitch I had forgotten I had coming. They delights of old age! Regards Andrew PS now what was I going to do with it.

Stand in the middle of the road with a placard. Given you record you should have a DPD gold card to go with your frequent flyer cards. Regards Andrew

Clearly a space time warp if he was 30 years up the road. 😉😱 Regards Andrew

F number can be used in different ways. As discussed above for exposure speed but also the maximum steepness of the light rays for matching accessories like filters, correctors and spectroscope and for calculating effective focal length for image scale. Regards Andrew.

A jewel box of colours. Bright and sparkling a good contrast to all those H alpha emission nebula. Regards Andrew

Yes looking good as Robin said. Regards Andrew

The advantage of the big mirror at Big Bear is that they can do high temporal cadance observation at both high spatial and spectral resolution. Often in many simultaneous wave lengths. Regards Andrew

I always take darks in the dark just to be sure. Light leaks can also be an issue for flats. Regards Andrew

Have a look at this "Accordingly, a thinner vane will diffract less light, and additionally will diffract this light farther away from the star (or planet)." from http://www.astrosurf.com/viladrich/astro/instrument/sensitivity/spider-diffraction.htm Regards Andrew More information here https://www.telescope-optics.net/spherical1_files/spider.htm and here https://www.telescope-optics.net/spider.htm

To really understand this you need to look at the maths. However, maybe this will help. You can work out what an obstruction will do by treating it as a hole and then inverting it by subtracting the intensity from the rest of the calculation. In your edge model the wider the veins the further apart the edges are, this alone has an effect. Regards Andrew

No the whole obscured area contributes contributes to the diffraction pattern. Regards Andrew

It is the relatively fat spider vanes that do it. This puts more light into the spikes. Regards Andrew

Dew shades both reduce the angle on the sky the optic can radiate into and limits the air flow near the optic which reduces the moisture that can condense on it from the air. Dew heater heat the optic counting the radiation loss. Regards Andrew

Basically objects radiate proportional to T^4 so the sky radiates very little back the wall a lot more. So as @Stu said the mirror will continue radiating to the sky and fall below ambient. Regards Andrew

When pointing to the sky the mirror will radiate its heat to the sky which is close to 4k and vice versa. When pointing to say a wall it will radiate to the wall at say 4c etc. It might reach equilibrium with the wall but not the sky! Regards Andrew

Hi @robin_astro, unfortunately the spectra was contaminated with that of another star. I will have to do it again with a different position angle. Regards Andrew

Should not damage your scope. Years ago I had a brass RSA threaded eyepiece freeze to my eye! Too wimpy now observe remotely from a warm room. Regards Andrew

@PhotoGav very roughly our old idea that GC were old is wrong and due to selection effects prior to IR ccd and hst. There are gc of all ages and a continuum of clusters from compact gc to open clusters. What you get depends on just how massive and dense the gas cloud they formed in. gc form today in regions where galaxies are colliding and other situations triggering star bursts. gc can be used to trace galaxy mergers as gc with common properties come from different source galaxies. They can be used to trace the star streams from the mergers as have been done for the milkyway and other large galaxies. Regards Andrew

@robin_astro interesting idea. I will have look. Not sure how good the spectra are as I did not seek to avoid other stars/spectra in this trial. Could always do it again though. Regards Andrew