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andrew s

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Everything posted by andrew s

  1. Not what the OP asked for but you can see relativistic effects with a compass. Put it near a wire carrying a current and it will deflect. The magnetic field round the wire is the relativistic effect of the moving electric charges. Regards Andrew
  2. Yes it is it is the same equation for the Schwarzschild radius https://en.m.wikipedia.org/wiki/Schwarzschild_radius which defines the event horizon for a non rotating spherical mass. Regards Andrew
  3. I think you can. Firstly, the event horizon forms round a collapsing massive star before the singularity forms and secondly if you were outside a massive enough spherically distributed mass that was not dense enough to form a singularity (maybe as a thin shell of material). Regards Andrew
  4. We are blessed with wide choice of excellent CCD and CMOS cameras. Think yourselves luck we have moved on from trying to hypersensitise film to a fraction of the performance of even the worst of those available today. Regards Andrew
  5. Measuring the Hubble "constant" is not a simple matter of taking a measurement. To get from the measured values to H requires much theory and in many cases poorly known values for example in nuclear reaction rates and hence stellar evolution. It is in some ways amazing that it is as close as it is given these constraints. Just going from the CMB era H to H today requires a model where H changes by many orders of magnitude. Regards Andrew
  6. Two points. The speed of light measured locally is a constant. There is a lot of different coordinate speeds of light depending on the coordinate system chosen including ones related to the expansion of the Universe. Cosmological distance is dependant on the model chosen and on the exact distance requested. I.e. the distance when the light was emitted or when received. The Universe is to a good approximation on a large enough scale homogeneous and isotropic so all points are equivalent so no special point to expand from. Also the expansion is not any kind of explosion from a point. It is a change in metrical scale everywhere. Regards Andrew
  7. Yes I use CMOS. The best modern backed thinned CMOS camera are as good as and often better than the equivalent CCD cameras. The only remaining issues is that due to the mass market the pixels are small. This can be used to advantage in removing the telegraph noise CMOS produces. Have a look at C Buil's site http://www.astrosurf.com/buil/index.html for some reviews. Regards Andrew The higher read noise in CCD cameras reduces the effective but depth so not a lot of difference but newer CMOS are 14 or 16 bit now.
  8. Try looking up in the aavso data base. I am sure it will have both V and B estimates but expect it to vary. In fact for such stars V-B varies considerably. I would not worry about it though just give it a go. Wikipedia gives 0.181 for v-b Regards Andrew
  9. Yes the spectral type varies as the star goes through its cycle. rr Lyr is the exemplar for a class of variables. You can find lots of info in the web about it and them. Try the astro database SIMBAD to look up the star for its V and B magnitudes. Regards Andrew
  10. Actually we can say gravity worked up to and beyond 10000yrs ago by looking at suitably distant galaxies. Regards Andrew
  11. Nothing in Science is fully understood. We have models that work well or less well at predicting observable effects. We judge a theory on its usefulness and to a degree its elegance. No one know what energy or entropy "really "are. We are more familiar with energy so feel comfortable with it as opposed to say entropy. Regards Andrew
  12. The simplest theory of dark energy is a very small non zero curvature to spacetime I.e. a small cosmological constant. Regards Andrew
  13. Sorry @ollypenrice the Universe is and always have been spatially infinite according to the best current theory. This has nothing to do with the speed of light or the age of the Universe. Regards Andrew
  14. The current best theory us that the Universe is spatially infinite and always has been! Spacetime (not space) was finite at t=0 and has been expanding ever since. The greatestest distance we can see is called the observable Universe and is from the CMB we see to day. It is further (in light years) than the age of the Universe because of the metrical expansion in the Universe. The most distant objects we can image are receeding faster than the speed of light due to the expansion but that is due to space expanding not the kinematics of the objects. Regards Andrew @Vladi listed while I was posting this
  15. All the skills (or did have in my youth) but for "Keeping a clean, tidy, organised production area.". Also my arm won't reach form my couch to Exeter. Regards Andrew
  16. The debris might just be on an intersecting orbit with high eccentricity and or inclination. However, I doubt he could have eyeballed the calculation. Guess that's why it's called science fiction. Regards Andrew
  17. The cost of a mirror depends on its shape (spherical, parabolic, hyperbolic) and how accurate its figure is. The epsilon also has a first class corrector. The mechanics are very good to. Regards Andrew
  18. For what's worth the pros use etendue to define their telescopes/instruments. Roughly, this is aperture ^2 x field of view for imaging instruments. They are normally intent on getting as wide a field as deep as possible in the shortest time. They the make a detector to match. Focal length comes into play for field size but also corrected field size depending on optical design. For example a corrected Newtonian compared to a standard one of the same aperture and focal length. So it's not just aperture but also the size of the corrected field and then the detector to match seeing and field size. You can disregard the elements that don't apply to your imaging aims e.g. small field for planets and most galaxies. Regards Andrew PS Remind me what is an eyepiece? PPS @ollypenrice your a very naughty boy.
  19. Yes but they will be model dependant . Currently the best accepted model is the LCDM one. Regards Andrew
  20. You have to define the criteria for winning. Total photons collected or per pixel or mm^2 etc. Regards Andrew
  21. Your clearly kneading confirmation @mikeDnight son. Regards Andrew
  22. We can but speak our own truth. Regards Andrew
  23. The post above was a joke please treat it as such. Regards Andrew PS honest
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