Last updated: 15 July 2003
Sent: Sunday, July 13, 2003 18:16:23 From: firstname.lastname@example.org (Marvin C. Sumner) I've seen a few notes in Mike's pages that suggest some folks don't understand this subject, so here is a little tutorial: Realize that as computers in telescopes and other places calculate the positions of celestial objects (stars, planets, satellites, etc.) the date & time reference must be Greenwich Mean Time (GMT). Thats because latitude & longitude and celestial time-keeping (and other astronomy factors) start there. Now, most folks have clocks and calendars that can be quite accurate enough for our needs, but they read LOCAL time (the time that you get up, feed the chickens and go to work). Your calendar flips to the next day at LOCAL midnight. Also, your clock includes the use or non-use of daylight savings time (DST). The folks at Meade know all this, so they have the Autostar asking for LOCAL date, time, time-zone and whether or not DST is in use. The date, time and DST are entered at start-up and the Time-Zone is included in the description of the observing site. The Autostar will use your input data to convert local time/date to GMT, then proceed with its calculations. Remember that when folks in North America (and the rest of the Western hemisphere) are setting up for an evenings observing, its already the next day GMT (in England). The scope's computer will do the time conversion math first, then if the answer is greater than 24 hours (military time) it will add ONE to the date and subtract 24 from the time. (Month and year turn-overs complicate it a bit). The bottom line: Don't try to out-guess the Autostar's time-keeping system. Give it the parameters it needs as accurately as you can & "turn it loose". Marv Sumner
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