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About acey

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    Deep-sky observer

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  1. Proton decay has not been observed (unless you know something I don't). In string theory there are no actual vibrating bits of string - they don't run out of energy or "slow down". I share your scepticism, though possibly for different reasons.
  2. A planisphere to see what's due south (therefore at its highest in the sky) for the time and date when you're viewing. Then S&T Pocket Atlas to star hop with the finder. Then, at a dark site with decent aperture, a more detailed atlas to locate the exact position of the target (Uranometria, Millennium Star Atlas, Great Atlas Of The Sky, TriAtlas C, whatever). With an 8-inch I found SkyAtlas 2000 sufficient for steps 2 and 3. My planisphere is one of the few things that has served me at all stages of the hobby. Its simplicity is its greatest virtue.
  3. Why would the hopeful beginner walk into a department store rather than look online? In the department store they'll most likely be told "We don't stock telescopes." And even if they do, the assistant won't know anything about astronomy.
  4. Sure. If it's anti-reflection coated it'll only cause a small amount of light loss and if it's of high enough quality it won't distort the image unduly. But it'll be expensive and it'll dew up quickly unless you take further measures. And, er, it'll get dusty. So what's the point?
  5. http://www.convertalot.com/celestial_horizon_co-ordinates_calculator.html http://star-www.st-and.ac.uk/~fv/webnotes/chapter7.htm
  6. What you are saying would make sense if the celestial equator was a circle running parallel to your horizon right round the sky (at an altitude, let's say, of 56 degrees). But it isn't. If you look south then the equator is 56 degrees above horizon This is declination zero. Turn and look north and the thing you'll see 56 degrees above horizon is Polaris, which has a declination of 90 degrees. The Wixey tells you the altitude of things above horizontal. The celestial equator is tilted with respect to the horizon. Declination and Right Ascension are fixed co-ordinates on the celestial spher
  7. The Wixey is an inclinometer - it measures angles with respect to horizontal. So you can use it to measure the angle of a target above the horizon (i.e. altitude). That is completely different from its declination. What you suggest would give declination only for targets on the meridian. To use the Wixey as a "goto" you also need a way to measure the azimuth of the target, then use an app to convert altitude-azimuth to declination-RA. Otherwise use the Wixey (with telescope) as a sextant - i.e. measure stellar altitudes. Or in place of as a spirit level when putting up shelves.
  8. A scope with aperture A and central obstruction diameter D has effective clear aperture sqrt(A^2-D^2). I don't know D for an 8" SCT but that's how you'd work out the aperture of a refractor with the same light grasp. Though of course there's far more to a scope's performance than light-grasp, as the comments in this thread illustrate. For example, if an 8" SCT had central obstruction 3" then the effective clear aperture would be sqrt(64-9) = 7.4 inches. A 7.4 inch refractor with the same optical quality as an 8" SCT would be expected to have the same limiting magnitude for stars, but slig
  9. I'd never heard of Orion's Belt being called the Three Sisters, but it's apparently a recognised name (on Wikipedia at any rate): https://en.wikipedia.org/wiki/Orion's_Belt
  10. Whoever said that was wrong. Gravitational waves interact with matter: that's how they were detected. When gravitational waves meet any matter they have an effect of stretching and squeezing it (quadrupole radiation) - this causes some heating so the waves lose some energy. The effect is tiny which is why it took about a century between predicting their existence and directly measuring them. Even then it had to be an incredibly powerful source: a pair of colliding black holes. Gravitational waves can refract, diffract etc, analogously to electromagnetic ones (with the proviso of quadrupole rat
  11. Was asked recently in another thread...
  12. Tighten the clips sufficiently to hold the mirror in place. Don't worry about pinched optics, thermal expansion etc, a slipping mirror will do far more to harm views. Don't test by rotating the mirror beneath the clips as you may scratch the mirror edge. To check that your mirror is sufficiently well held, tighten down the clips until they seem to be holding the mirror without unduly pressing, collimate the scope, and check that it maintains collimation at all angles of altitde. An overly loose mirror will go out of collimation when the scope is tilted, a sufficiently rigid mirror is one that
  13. I wouldn't wash any mirror with a coating less than a year old. I made the mistake with my first scope and scratched the mirror (though the scratch was very fine and did nothing to the view). A couple of weeks ago I washed the primary and secondary of my 12" flextube - it was about 5 years since last time so I figured they could do with it. I cleaned them the same way I wash my specs every day: under the kitchen tap with washing up liquid, using my finger to rub clean. (Pauses for gasps of horror...) With a cotton wool ball you can probably feel grit down to about a tenth of a m
  14. Glad you liked my post about dark sites Yes, I pack my gear in my car and drive 25 miles to a remote spot down a minor road with almost no through traffic. I chose the spot a few years ago after my previous one started to be encroached upon too much by a light dome on the southern horizon. I found it by looking at the OS map for reachable rural spots likely to have a clear, unlit southern horizon, went in daytime to check it out, and saw there would be easy parking that wouldn't obstruct anyone. Sitting alone there in the middle of the night I feel far safer than I would walking down any
  15. Look through the focuser without eyepiece. Every area you can see should be blackened/shielded/flocked to stop stray light entering the eyepiece. Usually means the area opposite the focuser, top of secondary and interior of focuser tube (and part of the dewshield). I found it led to some reduction of stray light issues on bright targets at my dark site (diffraction spikes were slightly less prominent). No difference on faint targets.
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