>> Ordinary? You mean something like a Wild T-2 or Kern DKM-2. Even then >> getting close to 1 arc-second requires a lot of care. > > A wild T1 reads directly to 6 seconds, but with repetition will get 1 > second. > Unlike digital instruments you need a little bit of skill and > persistence to get the best measurement from an analogue instrument.
Assuming youcan do that w/o bias. A T-2 ius a 1 ard second instrument, a T-3 is 0.1 arc-second. I've never seen a T-4 in the flesh. >>> You observe circumpolar stars at night to obtain a true azimuth. >>> (North and South) and also the latitude by the inclination of the pole. That means observations over more than 18 hours. It'll take you most of a year, unless you are above the artic circle. >> Not quite so straight forward. You have to have accurate siderial >> time and an almanac. Polaris is only near the pole, not at it. > > No need for time, you follow the azimuth of the star until it turns > around and then again until it turns back. Half the difference gives you > the azimuth of the pole very accurately. See above. > Fit your observations to a > parabola to get a good result. > Works best in Winter when the sun is down for more than 12 hours. A > good technique as refraction errors cancel. In practice, the "seeing" is nowhere near 1 arc-second for 2-3" aperture 'scopes. >>> On a time photograph these stars draw circles around the pole, the >>> centre of the circle >>> is the celestial pole and its elevation above the horizon gives the >>> latitude. And to do that you need a sub-arc second telescope mount. You just can't mount a camera on a tripod. >>> You can also use an almanac and a calendar to determine your latitude >>> by observing stars >>> with the theodolite. >> >> Not so easy. At the celestial equator the stars are moving in Hour >> Angle at 15 arc-seconds per second. >> > > As I said, analogue measurements need some skill and perseverance. That's an understatement. I've done it, both for North lines and to adjust a 24" telescope. > If you added more modern technology you could track your theodolite/ > telescope with a clock so you would get a longer period to adjust/ > observe the observations and set your clock. > > Neville The "modern technology" just makes the angle readout direct. -John ============== _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
