andrew s

@vlaiv nice series of post with clear demonstrations Regards Andrew PS If you feel like it you might like to compare a bark line on a light background with a light line on a dark back ground.

You have to remember even the gods at Takahashi provide telescopes with issues as on noted by threads on SGL. Poor focusers and funny stars in the corners on some models. Regards Andrew

@Gina, I have been watching your heroic efforts but do wonder if the physical properties of your material is suitable for a clock escapement. I don't know what they are but I suspect they are quite different from traditional material (brass ?). I would worry about Youngs modulus , creep, coefficient of restitution and coefficient of friction for a start! Nevertheless I hope you succeed. Regards Andrew

Additionally, you can get narrow band filters designed for fast optics which correct for the band pass shift. Regards Andrew

I have had 4 mirrors and 3 telescopes from OO and all have been first class. Regards Andrew

A flat field should remove it. Regards Andrew

It looks like a dust mote on or near the sensor. It is revealed in the converging light of the telescope but with uniform illumination it won't show up as much if at all. Regards Andrew

What you are missing is local siderial time LST. A stars RA is, for a given epoch fixed, and your LST will tell you which RA is now on your meridian. As stars moves due to precession and proper motion you need to use Jnow but your program will take that into account for you. Regards Andrew

There have been a number of posts on flats not working, stay light and the like. I came across the attached some years ago but was prompted to look it out as it describes an easy way to see what's going on by using your rig and a pinhole to image its internal and see where the issue are. Here is the paper Detection of scattered light in telescopes. Regards Andrew

I seem to recall that you can transform G to V. Also you can use clear for some projects. @JeremyS is your man as he is director of the BAA Variable Star section and I am sure he can point you in the right direction. Regards Andrew

You can defocus the stars to reduce saturation. It can also improve the s/n ratio. Have a look here https://www.aavso.org/dslr-camera-photometry-guide Regards Andrew

If the Barlow is placed too far in (more than its focal length inside the native focal point) then the telescope plus Barlow will not produce a real image. Regards Andrew

Should be good. He gave a similar talk to the Chester Astronomical Society and I contributed some date in the summer. Nice to have an update. Regards Andrew

I noticed it and another https://arxiv.org/abs/2101.09837 related paper this morning. Looking like SO2 is getting more and more likely as I suspected. Possibly a modern day canals on Mars. Seeing what you seek? Regards Andrew

This is what I got looking at two lines with my now retired homemade temperature controlled echelle spectrograph. Regards Andrew

Good post @rl I had forgotten about helio and stellar seismology. I love the idea of spin cast araldite mirrors. Regards Andrew

I don't know the answer to your question but if I was trying to find out the limits of what's possible I would look up the details of the measurements made by the gaia satellite. Certainly accuracy will depend on how bright the star is etc. The other area to explore would be the planet hunting spectrographs. Regards Andrew

Try centering a star sync on it. Do a slew away then back if it's not centred then you have backlash or other hysteresis which needs to be removed before you can get accurate pointing. Try different directions for the slew. I don't know your system / software so can't be more specific. Regards Andrew

Very impressive as usual. Regards Andrew

In general relativity red shift is only separable into components in simple cases. You cannot in general say this bit is due to gravity, this bit is due to velocity or cosmic expansion. The surface gravity of a star is a function of its size and mass. Giant stars have a lower surface gravity than their dwaf counterparts of the same spectral class. This shows up in the shape of the spectral lines. Regards Andrew

Brilliant indeed!

Thanks very clear but I don't see how this is different from normal vignetting. It looks just like an extreme form . Regards Andrew

This is equivalent to asking for the mass. It is not possible to do this directly for an isolated star. You can get an estimate from its spectral class as this is related to (amongst other things) mass. Regards Andrew

As far as I know, yes. Regards Andrew

As you say, transverse motion is measured by their proper motion (shift) against the more distant galaxies and quasars. The accuracy of these measurements has been improved by the Gaia satellite but there are limits to how small a shift we can detect. So yes we could miss fast distant stars. A proxy for closeness to us is high proper motion. Regards Andrew