andrew s

Fine work, impressive. Regards Andrew

Your setup is obscenely good 😏 Regards Andrew

@vlaiv I don't think you can be definitive as eyesight varies. However, in telescope-optics.net section 6.6.1 is a diagram with plots including bright, dim and high low contrast thresholds introduced by Rutten and Venrooij. Maybe this will help. Regards Andrew

On the eye, it has the least aberation at 2 to 3mm entrance pupil. Also if you want to have the best eye resolution you need to excite the cones. So you need to present the eye with an exit pupil of 2 to 3mm with an intensity high enough for colour vision to get the maximum from the image or at least that's how I understand it. If the intensity is high enough the eye is limited by the "fast" seeing not the long term that limits imaging. Regards Andrew

If you eat enough you could become a gas giant! 💨 Regards Andrew

While eating mince pies will increase your rest mass it has no effect on your rate of aging. May be (non) woke but that's a fact. Only other will see you differently! 😜 Regards Andrew

You need to be careful about who's clock. Your own clock always ticks at one second per second. Others see it tick at different rate depending on their velocity relative to you. Regards Andrew

Yes block time or rather spacetime is a well defined theory if not main stream. Discrete time or space at the Plank scale is just speculation. There is no evidence for it even though it has been looked for. While many scientists believe in it none of our current theories use anything but continuous space and time. Regards Andrew

I time travel all the time. I just do it in one direction one second at a time. Not fallen of the earth yet. 🦄 👨‍🚀 Regards

Now it's in your observatory you should not need to do it again, a least for a long time. Regards Andrew

Fine image, the cluster is nicely set off by the bright stars. Regards Andrew

Thanks that's what I intended "proper motion" Regards Andrew

Having given this some thought the simplest idea I can come up with is to view the field of a star with high proper motion. It current position will with a simple calculation give the date. Regards Andrew Ps corrected ascoointed out by @Xilman

Been experimenting with extracting flat fields from my low resolution spectra fields. The current attempt has been running since 9pm last night and not yet finished! However, I have spotted a flaw in the approach in that the FF will be an approximation just where you need it to be most accurate! Just don't have the heart to stop it. Regards Andrew

You could use the precise position of the pole. Not too difficult for an AI. Regards Andrew

Check star also warns you if you comparison star(s) is, unexpectedly, varying. Regards Andrew

It's not uncommon to defocus the image in photometry so that the image is over sampled. This minimises the pixel to pixel variations which together with guide errors add to the noise. Regards Andrew

The only things I could think that could behave as required was an alien space craft or one of ours time traveling back in time to check what actually happened. Regards Andrew

Spot diagrams are the result of ray tracing using geometric optics and don't therefore takes account of diffraction. Things to consider would be: Are the spots larger than the diffraction limit or not. How to they compare to your pixel size. How do they compare to you guiding accuracy and or local seeing. What use do you want to put it to. I see @vlaiv has given a comprehensive account while I was typing. Regards Andrew

@PhotoGav it a high gain arial optimised for Garves so I am not surprised. If you're worried rig up a simple dipole and compare the results. Glad it's working so well. Regards Andrew

It was a symbiotic advantage. The engulfing prokaryotes gave the mitochondria nourishment while the mitochondria allowed the prokaryotes to exploit the energy available in an oxygen atmosphere. The oxygen was at a much lower level than today but was death to organisms that evolved in the initial reducing environment. This book it a fascinating read Revolutions that made the earth Regards Andrew

Could not resist while waiting for my target to rise 13x10s just median combined. Different PA to @robin_astro's image but I was in a rush! WR5 will make a good wavelength star Regards Andrew

I not sure I can unpick this but I will try. When we say the universe is homogeneous and isotropic we mean anyone anywhere will see essentially the same thing on a large enough scale. This seemsis by the uniformity of the CMB to 1 part in 10^5. There is no special place. No center of an explosion. Nothing material can travel at or faster than the speed of light and from its gravitational effect we know dark matter is material in this sense. Hot relativistic (moving close to the speed of light) dark matter has and is being researched but cold (slow moving) dark matter fits better to current observations. In our cosmological models based on GR time dilation due to velocity and gravity are accounted for. What we see does depend on how fast we are moving but movement has to be relative to something. I am doing all possible speeds now relative to one thing or another in the Universe (but less than c). We know how to account for this. Regards Andrew

This is true as is the fact the Hubble constant is falling asymptotically. How can they both be true? While the "rate of expansion" in the quote refers to the scale factor 'a', the expansion rate as measured by the Hubble constant is the ratio of the rate of change of a to a i.e. ( da/dt)/a. The acceleration in a is positive i.e. ( d2a/dt^2 > 0) The recessional velocity of a galaxy at a given distance (v = HD) is getting slower in units of Km/s per MPc Strange but true. Regards Andrew

What I said was it is assumed to be the same ( on large scales ) at the same epoch. If this were not the case the the CMB would not be as uniform as it is. Yes it started in a hot dense state and has been cooling ever since. The expansion is of the "scale factor" not a normal expansion as say when you heat a bar of metal. As in the example of the balloon being blown up, the spot on the surface get further apart but locally the spots don't move. If the expansion of the scale factor is positive then as you look further away they appear to be receding faster and faster (Hubble's Law). Eventually you reach what is call the Hubble sphere where the speed of recession is equal to the speed of light. We can currently see objects receding out to about 3c. As I said it was very fast initially, as measured by the Hubble constant, and is slowing down. However, there is no single speed as it depends on how far away you look. See this for some background Scale_factor_(cosmology) I don't understand what these bits mean. Regards Andrew