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RELATING AN OBSERVED EVENT TO
STANDARD TIME SYSTEM SUCH AS UTC
1. UTC and your Local Time
When reporting results, we need a link to accurate Standard Time.
Most easily accessible is UTC (Coordinated Universal
Time). In most cases it is sufficient to report
your results in UTC; if necessary this can be converted into another time
system. Where you see predicted times listed in UT, this could
mean UTC or UT1, but - for prediction purposes - it is generally OK to
assume UTC. On the other hand, when reporting
results you need to be specific what time system you were using.
All these time systems use a 24 hour clock system (no am/pm). The
three Australian Standard Time zones are based on UTC, adjusted for longitude.
* AEST = Australian Eastern Standard Time = UTC + 10 hours (centred on 150° East longitude)
* Daylight Saving ("Summer") Time in this same zone = UTC + 11 hours
In all the different time "zones", the precise start of a second or a minute are the same.
Such a 10 or 11 hours time difference can move you into the next day (or back into the previous day). For example, if an event is predicted on July 6 at 16h 15m UTC, then for us the time will be 16:15 UTC + 10h = 26:15 AEST (more than 24) = 02:15 AEST on the next day, which is 2:15 am on July 7.
Knowing your local time, you can also work backwards and find UTC by
subtracting 10 hours (or 11 hours in the summer) again making sure you
keep track of the day as well:
Example 1: 7:56 pm AEST = 19:56 AEST = 09:56 UTC on the same day
Example 2: 3:22 am AEST = 03:22 AEST = 27:33 AEST previous day = 17:33 UTC the previous day
2. HOW TO RELATE AN OBSERVED EVENT TO UTC
The event has to be observed and its time compared with the time reference.
In this comparison there will be a delay and an error. For a single
event a stopwatch is OK, but even here a tape recorder can be very useful
when e.g. an unexpected extra occultation is seen or to correct a mistake
without taking your eye off the telescope. For long or multiple events,
like an asteroidal occultation or a graze, a continuous recording of the
time and your voice on tape is necessary.
Standard quartz digital watches with a stopwatch function are now very accurate and available at bargain prices. The only drawback of the cheaper watches could be the very small size of the buttons. For more "de luxe" controls, you may want a full size digital stopwatch. If you buy a large stopwatch, look for one with many "lap timers", very handy (e.g. Tandy has a 9 lap model at $50).
One problem with all "human" timings is a small delay, the "personal equation" (PE), which is the human reaction time between the eye first noticing the event and the hand or voice responding appropriately. The "personal equation" (PE) for most people is around 0.3 sec, and often a random error or uncertainty of approximately ± 0.1 or ± 0.2 sec may need to be added.
The most common Stopwatch Method is used in
Some observers start the stopwatch when they observe the event and later stop it at a radio or telephone time second or minute marker, using the lap/split or the stop button. The first action has the usual personal equation reaction time delay. The second action, the stopping on a second, can be repeated as many times as needed because the lap action can re start. Also, because the radio time second markers are completely predictable, it is possible for the operator to mentally "tune in" and hit the lap button at exactly the correct moment. When in doubt, simply re do another lap time and repeat until satisfied. With care, the synchronization can be done reliably to within + 0.05 sec. However, the true accuracy of the timing is much worse, due to the human errors.
Other observers first start the stopwatch on a radio time signal, use the lap/split function a few times to check that it is running right ("synchronization"), and later use the lap (or stop) button to time the event. In both above cases, by intelligent use of the lap/split timer (if available), it is possible to time two closely spaced events in the dark, or quickly correct a mistake.
The Tape Recorder Method is a combination of
a tape recording and the stopwatch method:
It begins by recording the voice event marker and comments plus the radio time signal on a tape recorder. Later the tape can be played back many times and the event (e.g. your voice) on the tape is then compared against the UTC time markers on the same tape using a stopwatch similar to the method above, i.e. start on the event and stop on a known second or minute (or the other way around). This method requires the tape recorder to run evenly over the time between the "event" and the time marker that you use (this could be a full minute or a nearby known second). Please check the tape recorder by measuring the time from one minute marker on tape to the next with the stopwatch and see if it indeed reads 60.0 seconds. If not, you will need to make corrections.
There is human reaction time (PE) and error in all this, and it is strongly
recommended that you ask for assistance from an experienced observer. For
example, when you are making a timing after waiting for an "unexpected"
event (the occultation, or a voice word on the tape), this involves the
PE "personal equation" delay. But then, when the stopwatch is synchronized
against the time signal, your brain makes use of the "predictability" of
the clicks or pips in the time signal and you can press the lap or stop
button more accurately, because you know when the next beep is coming.