Accurate timing normally comes in 2 parts: (a) An accurate time reference (b) Accurately timing the difference between the reference and the satellite event. Traditionally stopwatches have been used for (b). I staryted with mechanical stopwatches, later electronic, for a while used a wristwatch with stopwatch action (rather fiddly in the dark). Make sure the stopwatch can time several events from the same reference time. For the time reference, most observers use radio time signals. In the UK (and probably some other countries) there are telephone time signals (the UK give 3 pips each 10 seconds, and are accurate to at least 0.1sec). Leo Barhorst and others use a clock permanently synchronised to a radio time signal, which simplifies things. I use an electronic clock connected to a computer, and a pushbutton connected to the computer. I just press the button, and the computer measures the time from the last 1-second clock tick to the press, giving the true time directly in the computer. This saves errors in reading stopwatches and typing in the times. You may have noticed some recent seesat postings about misread stopwatches and wrong time zones. I calibrate the clock with radio time signals. I have used a PC's internal clock(s), but (1) they are not so accurate (2) the clock you read when the computer is on is different to the battery-powered clock that keeps going when the PC is off; and so deviates at a different rate from UT. This can be allowed for. Does anyone know how to read the battery-powered clock directly? In emergency (or observing away from home) I go back to mechanical stopwatches: they are still working after my electronic ones have failed. Mike Waterman mike.waterman@marconi.com ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Wed Feb 14 2001 - 01:22:54 PST