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Everything posted by acey

  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.
  16. Some reasons why it can be hard to get a scope pointing at the right bit of sky: 1. Sky is too bright (light polluted), so few stars are visible and it's guesswork to point the scope initially at a bit of black. Far easier if you can start by aiming for a naked-eye star and working from there. 2. An inadequate map (too detailed or not detailed enough) so that once you start looking through the finder you can't be sure if you're looking at the star you thought. 3. Inadequately aligned finder. Check it in daytime or with a stationary object at night (Polaris or, *sigh*, distant st
  17. Male-female Newbie-veteran Amateur-professional Moon-haters, moon-lovers
  18. Your conditions are fairly typical for a suburban location. You should be able to see some of the most conspicuous DSOs (e.g. M42, M31, M13, M81/82, Double Cluster...), but less conspicuous Messiers (e.g. M1) will be a struggle while ones of low surface brightness (e.g. M33, M101) will most likely be impossible. To see M31 as anything more than a little fuzzy blob you'll need to get in your car. If you can get to a place where the Milky Way is easily visible with the naked eye then you can be confident of getting good views. That usually means a naked-eye limit of about 5.5 or better.
  19. The cross hairs are much closer to the eye than the virtual images from the mirrors - I can't focus on mine either. It doesn't matter to me since I never use them. For secondary alignment I use a laser, looking down the top of the tube and adjusting the secondary to get the red dot centred on the primary. If I were using the crosshairs I think I'd just tolerate a blurred view and get things reasonably centred: the primary is more critical. If the primary is correctly aligned with respect to the secondary then the only significant "risk" is that the secondary is rotated slightly with respect to
  20. Possible if you really had a clear horizon but in this case it looks like the setting sun may have been seen through distant trees in which case the "flash" could have been a final glimmer of light through foliage. If it was a green flash it would have looked distinctly green - that's how you'd know.
  21. Why not just use one of those things you see in pound shops for mounting a smartphone on a car windscreen? Or even better, just get used to using the finder - far simpler, not affected by magnetic fields, and won't spoil your dark adaptation
  22. Have you ever wondered what astronomers did before electric lights were invented? A candle or lantern could hamper dark adaptation as much as an LED. William Herschel got round it by dictating observations to his sister who sat inside a lit hut. A later astronomer (whose name escapes me) used the smouldering end of a cigar as his red light.
  23. The Viking spacecraft landed on Mars in 1976 and sampled the atmosphere there. A few years later the same proportions of gasses - a "signature" of Martian origin - was found trapped in microscopic bubbles in meteorite EETA 79001 from Antarctica. It was found there because rocks on top of ice fields are very conspicuous and can only have come from above. There are other ways of identifying Martian meteorites from their chemical composition, e.g. the proportions of different oxygen isotopes, and more than a hundred have been identified.
  24. It was his "last lecture" before MIT disowned him due to misconduct and removed his lectures from their site. They can still be found elsewhere online. https://en.wikipedia.org/wiki/Walter_Lewin_Lectures_on_Physics
  25. Don't get the biggest (largest aperture) scope you can afford unless you're sure you want the weight and bulk that comes with it. You say you mainly want to look at planets, which you can do from a light-polluted site, in which case transportability might not be an issue. But you still need to get it into your garden (if you have one). An 8" dob is a very good all-rounder and very manageable: the Skywatcher 200mm dob is currently £285. The 10" is £429 and is considerably bigger and heavier, the 12" (Flextube) is £529. I have the 12" and use it for deep-sky viewing at my dark site, but it's not
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