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Everything posted by Physicist13

  1. blow with little air..not frm a can! if you must but tht dust wont make a jot of difference to image or viewing quality. dont worry about it.
  2. from what I see you are calculating a formula for the uncertainty disc from uncertainty princip saying tht the momentum/wavelength is known. This gives a formula for a 'blob' of light passing through an aperture..but does not account for any diffraction. The airy disc is a diffraction feature and the 1.22 comes from the zero in the Bessel function. You might want to calc the 'smudge' of the airy disc due to the uncertainty princip.
  3. A little chipping in. The orig Q was also about "spin". this is a quantum property that is measurable but the word spin is just a handle..like colour is to quarks. The quantum spin behave a bit like classical spin which is why the term is used but as in all quantum realms is v different too. So try not to thing of it as something actually rotating like a top.... no point trying to picture anything in quantum tbh!! Yes Physicists do use specific words and phases which are often not clear and too many maybe...our main language is mathematics so to explain outside that phrases are used.. eg entanglement, coherence, etc. Not often v useful to non-physicists. Its a challenge to get info across..... Bck to orig. it was a bit of an apple and pear comparison (apple being v apt!) . gravity (by which I assume u mean the force that arises) (force will do for now,, ) is a diff quantity to velocity..thts a distance/time. why light doesnt escape a black hole (whic is neither a hole or black!) is simply the escape vel is greater than c. good for reading but u cant beat doing a course and talking face to face with people in the field. OU is vv good...... P
  4. sorry strongly disagree!!! This is whole point of the SI system!!! Units of angle is the radian and should be used. The CIMP recognise other units, such as degrees. With globalisation it is increasingly important that all countries use the same units and with national standards that maintain those units and their traceability to the SI system. P (metrologist! ) see www.bipm.org and links also ISO site. plus UK national measurement lab.... npl.co.uk
  5. yes it does dep on where the star is in its cycle..mass etc etc.... balance of sev factors.
  6. yep pretty much. Fusion is not a thermodynamic effect. Its a v diff way of producing energy and yes its the radiation pressure from this that countering gravity...not the fact that the core is hot. The radiation pressure is a net outward force as you say. Once the fuel is exhaused fusion stops so the radiation pressure drops dramatically. So the core then contracts under gravity and compresses more and heats akin to normal heating of a compressed gas. Once hot enough for the next fusion process to kick in then rad pressure is active again so further core compression halts....this process repeats though various fusion reactions. other processes also going on but thats main process.
  7. Sorry but QM def not a result of idle speculation!!!!
  8. hmmm trying to stay out of this ;)...but just to say. So far special Rel, Gen rel and QM have passed all the tests thrown at them to within the best achievable experimental limits. Experimentalists constantly try to do more precise measurements to keep testing these theories and possibly show a brakedown. In general, theorists modify or more rarely come up with new or refined theories that also have to pass all current tests but may also predict some new features which are measurable. Hypothetical arguments can be stimulating and thought provoking but must lead to some prediction of a verifiable experimental test.
  9. oh a light pollution filter will mk big differance unless you are in a partic dark sky area. Clip in ones for Canon are good.
  10. yep!! def interact and learn You WILL need to get motor for mount next! you have to track I'm afraid. bby steps though! Personally I'd keep off and software for now..just get used to doing single exp..focusing and tracking.... Most of all have FUN!!!
  11. steer away from planetary with DSLR (at least for now) ..its poss but much better and easier with "webcam" . High frame rate is required..over 100fps really... yes, high f ratio needed too. Moon is fine as single exp will do...although it does benifit from fast multi exp too. P
  12. Hi. I'd suggest you go in baby steps! Get used to the DSLR first. Why not try piggy back or ditect on your mount? Go for easy objects and use camera lenses to start. Always take in RAW ! learn to focus and get feel for how long an exp you can do before you notice trailing. Then try fixing to scope , and again go for big east targets..cluster?. Ring neb is v small. I'd avoid Jup and planets for now as diff techniques is needed. a bahtinov mask will be very useful. P
  13. the matter/anti-matter inbalance is v v interesting.....work is going on to produce long lived anti-hydrogen with aim to study and compare to normal H....spectroscopy may show differences....nobel on way to those who find something...
  14. I'd say try and do an OU course or some online course but one where you can interact with people and ask questions. FOr QM you def need the maths and learn the ability to interpret the maths in the physical world..bizarre though the results are. Books are great but it def needs human interaction too.... Dont be scared!! I got O level B in maths and C in A level!..... enthusiasm is the key!! P
  15. The random noise reduces as square root of number of images stacked, and the "signal" part goes as N , so overall signal to noise goes as root N . Basically a way of making say 10x1min exp=1x10min. Before anyone cherps up...read noise reduces this gain in SNR, which is why its important to get subs out of read noise if posisble.
  16. dont get too confused about the actual number for the constants..remember this is just what they are in the rather random units we choose. often theorists set them to unity .
  17. rule of thumb is to try and match the optical resolution to the camera (pixel) resolution. Thts usually where the f20-30 comes from. faster u can cap the better..but S/N drops so trade off, plus pc throughput...
  18. no expansion contribution, grav bound system. It only shows up on v v v large scales.
  19. lunar and planetary I use Lynkeoss and DSO I use Pixinsight, P
  20. PRL is about the hardest to get published in..its extensively peer reviewed. Many ref to calculations are given..longer papers on the discovery will follow.
  21. that article does only refer to taking images through standard camera lenses for which the lens info is known (ie distortions ets..so the camera automatically takes them out). His discussion on bias and dark is useful though! you need to know where your noise sources come from and if they are really random or not. "background" fitting routines can do the job of a "flat" to a pretty good extent. P
  22. apologies!!! my mind had read "binning" for some reason!! In fact dithering can improve resolution in undersampled images although it can be tricky to implement as often sub-pixel dithering is needed. The more common several pixel dithering is primarily a means of averaging out artifacts (eg hot pixels ). Drizzle is a form of dithering. I need more coffee!!
  23. the main thing is to know why you are dithering! Its a noise reduction technique but at the expense of resolution. P
  24. lol! both expts are about looking for "things" that theory predicts.....Physicists get very excited (we are def all kids!!) when experiment either does or doesnt agree with predictions. Often from the discrepant results comes new discoveries. consistance helps cement the theory but makes us want to push further.....to breaking point! "too crazy to be true"?? long given up the idea of "true" P
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