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Everything posted by Tiki

  1. Oh, and BTW is it simple enough to mount the tube rings to the altitude 'wheels' so that the wheels sit parallel?
  2. Thanks Moonshane and Quaoar . 3/4 ply it is then. I noticed on the "Dobstuff" site that they fabricate their altitude bearings with a lip that fits inside the rocker. It looks neat.
  3. Is this because of the broader footprint or is it due to other considerations?
  4. Thanks for the replies. Very true. Would a 3/8" thick altitude bearing be too skinny to be able to present a sufficient surface to the bearing pads?
  5. Largely inspired by Moonshane's post http://stargazerslounge.com/topic/105895-home-made-dobsonian-base/ I have decided to make a dobsonian mount for my OO 8" f4.5 newt. Smoothness and stability are for what I strive. Hindered by having never even used a dobsonian mount I have a few design queries: I would imagine that a larger diameter altitude bearing would be smoothest. Big means more weight, more materials and possibly not so pleasing on the eye. https://stellafane.org/tm/dob/ reckon that it is OK to go up to 1.8x tube diameter. 1.8 x 9"= 16" in my case. If I were to make the altitude bearings any smaller would much smoothness likely to be sacrificed? Moonshane's post quoted above suggests 70 deg. as the optimum angle for the altitude bearings to sit. Any reason to do otherwise? Would a 16" base diameter be too small? too jerky? too anything? Thanks in advance.
  6. Ignore the last post. I thought I had it.
  7. Three points on a great circle is a special case and the trigonometric identities will become much simplified. The cosine of one angle will equal the product of the sines of the other two angles. http://en.wikipedia.org/wiki/Spherical_trigonometry
  8. Find the great circle between two of the points and then see if the third point also lies on this great circle.
  9. 'Amateur astronomy twilight' begins at 23h 3m 1s in Southampton tonight. The calculator is good.
  10. Thanks Acey. I like the idea of 'Amateur astronomy twilight'. The calculator looks good too.
  11. How would SQM readings be affected in the two hours preceding the onset of astronomical twilight (assume astro twilight 00.39 until 04.34 in lat 51N)?
  12. Unfortunately in my corner of the cosmos, there never seems to be quite enough time. I would therefore rather buy a good usable mount if it takes too long to make one. Thanks for the replies.
  13. I have an 8" f4.5 OO Europa currently mounted on a Vixen SP. The time has come for a dobsonian mount and all its conveniences. As a seasoned alt-az user I am fussy and would need something smooth and well balanced. Can anyone recommend a good usable off the shelf mount? How are DIY mounts in terms of smoothness versus build time? Thanks in advance.
  14. Thanks for the replies. Ben's third link is spot on, it also has a link to enable you to plot your own charts with corresponding photometric data. http://www.aavso.org/vsp/.
  15. I would like to try and observe 3c 273. I need a chart that would show stars down to mag 13 or so. Are there any online resources where I could print the necessary region(s)?
  16. I use 216x, 154x and 110x with my 4" refractor. I often try 216x on the planets but it is only really of benefit a tiny proportion of the time.
  17. I find that even a little bit of skyglow makes most galaxies very difficult. I therefore have to be patient at home and wait for my targets to move into a favourable part of the sky. If for example you were able to observe M63 (small but reasonably bright) when it was somewhere near the zenith then M81/2 would be even more obvious unless LP is a factor. Your eyes need to be well dark-adapted too, some people use hoods etc. if there is too much stray light around. As Ed says, keep at it you will succeed.
  18. According to Dreadz's link, a very specific signal which will hopefully be monitored in 2015 by a new detector. A 'standard candle' valid over cosmological distances seems to be in the offing. As regards to near-collisions of rotating BH's some pretty funky orbits are possible. There is even a 'slingshot' type of orbit whereby the smaller will orbit several times round the larger before heading off (decelerating as it goes).
  19. Thanks. This is new news to me. I quite like the idea of a star that can give you frostbite. I wonder how many other cold stars abound?
  20. A ratio of the energies of the two impactors would be a good starting point and a decent first guesstimate. Eg. A ratio of 2.5:1 correlates to 1 mag difference.
  21. Interesting fact. Could you not use an online "asteroid strike calculator" to estimate the energy of the Tycho impactor in terms of the 2004 MareImbrium strike. It would only be approximate and subject to some simplifying assumptions but a first guess nevertheless.
  22. Depending where you are going in Asia you may have a decent view of the Sagittarius region of the MW. IMO, the best region of all but not so impressive from the UK on account of its measly altitude. Scorpio is also glorious from more southerly latitudes.
  23. A good explanation regarding polarization of the CMB can be found here. It was posted 3 weeks ago and is only 2 minutes long.
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